ANALYSIS OF THE AUGUST 14, 1980, RAINSTORM AND STORM RUNOFF TO THE SOUTH PLATTE RIVER IN THE SOUTHERN DENVER METROPOLITAN AREA, COLORADO U.S. GEOLOGICAL SURVEY Prepared in cooperation with the DENVER REGIONAL COUNCIL OF GOVERNMENTS , ,v>- JUN 2 8 i984 UNIVERSITY OF ILLINOIS at URBANA-CHAMPAIGfi ANALYSIS OF THE AUGUST 14, 1980, RAINSTORM AND STORM RUNOFF TO THE SOUTH PLATTE RIVER IN THE SOUTHERN DENVER METROPOLITAN AREA, COLORADO By Steven R. Blakely and Martha H. Mustard, U.S. Geological Survey; and John T. Doerfer, Denver Regional Council of Governments U.S. GEOLOGICAL SURVEY Water-Resources Investigations Report 83-4138 Prepared in cooperation with the DENVER REGIONAL COUNCIL OF GOVERNMENTS UNIVERSiTY OF ILLINOIS LIBRARV Lakewood, Colorado 1983 UNITED STATES DEPARTMENT OF THE INTERIOR WILLIAM P. CLARK, Secretary GEOLOGICAL SURVEY Dallas L. Peck, Director 4 - >0 For additional information write to: District Chief U.S. Geological Survey Box 25046, Mail Stop 415 Denver Federal Center Lakewood, CO 80225 For sale by: Open-File Services Section U.S. Geological Survey, MS 306 Western Distribution Branch Box 25425, Federal Center Denver, CO 80225 Telephone: (303) 234-5888 CONTENTS Page Glossary- vi Abstract- 1 Introduction- 1 Purpose and scope- 2 Data-collection methods- 2 Description of study area- 7 Monitoring station and basin descriptions- 8 06710000 South Platte River at Littleton- 8 06711500 Bear Creek at mouth, at Sheridan- 8 06711575 Harvard Gulch at Harvard Park, at Denver- 8 06711610 Sanderson Gulch at mouth, at Denver- 8 06711622 Weir Gulch at mouth, at Denver- 9 06711800 Lakewood Gulch at mouth, at Denver- 9 06713500 Cherry Creek at mouth, at Denver- 9 0671A000 South Platte River at 19th Street, at Denver- 9 06714130 South Platte River at 50th Avenue, at Denver- 9 Precipitation- 10 Basin characteristics, runoff, and runoff loads- 12 Event mean concentrations and water-quality standards- 25 Summary- 33 References- 35 ILLUSTRATIONS [Plates are in pocket] Plate 1. Map showing location of rain gages, water-quality and streamflow¬ monitoring stations, drainage basins and noncontributing areas, and rainfall data at rain gages for storm of August 14, 1980, southern Denver metropolitan area, Colorado. 2. Map showing location and area of monitored tributary basins, non¬ contributing areas within monitored tributary basins, unmonitored drainage areas, and basin rainfall and runoff for the storm of August 14, 1980, southern Denver metropolitan area, Colorado. 3. Precipitation maps based on radar-simulated rainfall data repre¬ senting six consecutive 15-minute intervals from 1400-1530 hours on August 14, 1980, southern Denver metropolitan area, Colorado. 4. Precipitation map based on radar-simulated rainfall data for 1330-1630 hours, August 14, 1980, southern Denver metropolitan area, Colorado. iii ILLUSTRAT IONS—Con t inued Page Figure 1. Map showing location of water-quality and streamflow-monitoring stations and study area- 3 2-7. Graphs showing: 2. Discharge and loads of total suspended solids versus time at Bear Creek, Harvard Gulch, and Sanderson Gulch during the storm of August 14, 1980- 15 3. Discharge and loads of total suspended solids versus time at Weir Gulch, Lakewood Gulch, and Cherry Creek during the storm of August 14, 1980- 16 4. Discharge and loads of total suspended solids versus time at the main-stem stations: South Platte River at Littleton, South Platte River at 19th Street, and South Platte River at 50th Avenue during the storm of August 14, 1980- 17 5. Discharge and concentrations of total suspended solids and selected metals versus time at Bear Creek at mouth, at Sheridan during the storm of August 14, 1980- 28 6. Discharge and concentrations of total suspended solids and selected metals versus time at the South Platte River at 19th Street during the storm of August 14, 1980-- 29 7. Discharge and concentrations of total suspended solids and selected metals versus time at the South Platte River at 50th Avenue during the storm of August 14, 1980- 30 TABLES Page Table 1. Land use, total area, effective impervious area, and urbanized area for tributary and main-stem basins and unmonitored and direct-flow areas within the study area- 6 2. Comparison of average basin rainfall for the storm of August 14, 1980, for tributary and main-stem basins as determined by the Thiessen polygon method and the radar-simulation method- 12 3. Total area, effective impervious area, rainfall, total runoff, storm runoff, and runoff-rainfall ratios for tributary and main-stem stations from the storm of August 14, 1980- 13 4. Storm-runoff loads for tributaries monitored during the storm of August 14, 1980- 19 5. Normalized storm-runoff loads for tributary and main-stem stations on the South Platte River for the storm of August 14, 1980- 21 iv TABLES—Continued Page Table 6. Basin characteristics, total runoff, storm runoff, and storm- runoff loads for the monitored tributary area, and percentage of value obtained for the South Platte River at 19th Street and the South Platte River at 50th Avenue for the storm of August 14, 1980- 22 7. Base flow, base-flow loads, storm runoff, and storm-runoff loads of the South Platte River at 19th Street and the South Platte River at 50th Avenue from the storm of August 14, 1980- 23 8. Event mean concentrations of selected constituents and properties in storm runoff from the tributary and main-stem stations on the South Platte River for the storm of August 14, 1980- 26 9. Event mean concentrations of selected constituents and properties in total runoff from the tributary and main-stem stations on the South Platte River for the storm of August 14, 1980- 27 10. Minimum number of hours that concentrations of selected metals exceeded Colorado water-quality standards for aquatic life at St reamflow-gaging stations on Bear Creek and on the South Platte River during the storm of August 14, 1980- 31 11. Specific conductance and pH in storm-runoff samples collected during the storm of August 14, 1980- 32 METRIC CONVERSION FACTORS Multiply By To obtain acre acre-inch acre-foot cubic foot cubic foot per second (ft^/s) degree Celsius (°C) foot inch mile pound pound per acre-inch 0.4047 10.28 1,233 0.02832 0.02832 (9/5°C+32)=F 0.3048 25.4 1.609 0.454 0.04416 pound per cubic foot (Ib/ft^) square mile 16,020 2.590 hectare hectare-millimeter cubic meter cubic meter cubic meter per second degree Fahrenheit meter millimeter kilometer kilogram kilogram per hectare-millimeter milligram per liter square kilometer V GLOSSARY average basin rainfall .—The area-weighted average of the individual rainfall quantities represented by each Thiessen polygon within that basin. Average basin rainfall is calculated by multiplying the rainfall for each polygon (which represents a rain gage) times the proportion of total basin area rep¬ resented by the area of that polygon which is within the basin and by summing the resulting values. Average basin rainfall (inches) n Precipitation in polygon (inches) i=l Polygon, area _in basin_ Total basin area where n=number of polygons in the basin. base flow .—That part of the total runoff which is not due to storm runoff. baseload .—The quantity of a constituent that is carried by base flow. It is cal¬ culated as the product of the base flow, the base-flow concentration, and the runoff period. convective storm .—A type of rainstorm caused by a warm, moist air mass rising through cooler air (usually due to solar warming). Subsequent adiabatic ex¬ pansion cools the warm air mass to the point of saturation, and rain falls- as a thundershower. A convective storm may last from a few seconds to a few hours. detention structure .—A structure which controls the flow in a channel and which causes water to be stored temporarily, part of it being detained until the stream can safely transport the normal flow plus the released water. This detention commonly results in suspended material settling out of suspension to become part of the bed material. effective impervious area .—An impervious area which is hydraulically connected to an improved conveyance channel or to other impervious areas which transport the runoff out of the area, such as a roof which drains onto driveways, streets, sidewalks, or paved parking lots. event mean concentration in storm runoff .—The flow-weighted average concentration of a constituent in storm runoff. It is calculated by dividing the storm- runoff load by the storm-runoff volume. event mean concentration in total runoff .—The flow-weighted average concentration of a constituent in the total runoff during a storm. It is calculated by dividing the total constituent load by the total runoff volume. gaging .—Refers to the measurement of precipitation or streamflow. ground truth .—Data collected on or near the surface of the Earth in conjunction with a remote-sensing survey. In this study, rainfall ground truth data was used to calibrate a mathematical model providing radar-simulated rainfall data. hydrograph .—Graph of discharge versus time. land use .—A term which relates to both the physical characteristics of the land surface and the human activities associated with the land surface. main-stem sites .—Those monitoring sites (or stations) on the South Platte River. National Geodetic Vertical Datum of 1929 (NGVD of 1929) .—A geodetic datum derived from a general adjustment of the first-order level nets of both the United States and Canada in 1929, formerly called mean sea level. NGVD of 1929 is referred to as sea level in this report. vi network .—A group of gaging or sampling points located in such a manner as to allow collection of areally representative samples of the medium involved in any process (such as rainfall or runoff) occurring within a geographic region. pervious area .—An area of porous material that allows infiltration of water, such as lawns, vacant lots, or agricultural fields. pixel .—In a digitized image, the area represented by each digital value. In this study, a pixel refers to the smallest measurable division on the radar- reflectivity map. This division is approximately 1 square mile. radar-simulated rainfall data .—Data that are used to indicate total rainfall quantities. These data are developed using regression equations derived from radar-reflectivity data and rain-gage data. runoff load .—Refers to that quantity of a water-quality constituent that is transported by the storm runoff. Runoff load is calculated as total load minus the baseload during the period of storm runoff. runoff period .—The time period from the start of a storm when runoff begins to exceed the base flow and ending with a return to base flow. sampling .—Refers to the collection of water samples for the analysis of water properties or chemical constituents. storm runoff .—Storm-generated surface runoff. Storm runoff is calculated as total runoff minus base flow during the runoff period. Thiessen method .—A method for estimating the average rainfall in a basin from rainfall data collected at rain gages located in the area. The gages are plotted on a map, and lines connecting these gages are drawn. Perpendicular bisectors of these connecting lines form polygons around each rain gage. The sides of each polygon are the boundaries of the area represented by each rain gage. The area (in acres) of each polygon within the basin is determined by planimetry from the map and is expressed as a percentage of the total area of the basin. Area-weighted average rainfall for the total basin area is computed by multiplying the total rainfall measured at each rain gage by its assigned area percentage and by summing the results. total load .—The total quantity of a constituent that is transported by the total runoff (base flow and storm runoff). total runoff for the runoff period .—The volume of base flow and storm runoff dur¬ ing the runoff period. The volume of total runoff is calculated as the area under the hydrograph for the runoff period. upslope storm .—A type of storm caused by upward movement of a warm moisture-laden mass of air when the air mass is forced up the slope of a mountain range or land mass by prevailing winds. As the warm air mass rises it expands adiaba- tically, its temperature decreases, and the moisture condenses into rain when the dew point is reached. Typically, an upslope storm is slower in forming and the precipitation intensity is not as great as a convective-type storm, but the upslope type often lasts longer (several hours to several days). In Denver, where prevailing winds aloft are normally westerly, upslope condi¬ tions are produced when easterly winds transporting moisture from the Gulf Coast are forced upward by the mountains on the west. vii Digitized by the Internet Archive in 2019 with funding from University of Illinois Urbana-Champaign Alternates https://archive.org/details/analysisofaugust8341blak ANALYSIS OF THE AUGUST 14, 1980, RAINFALL AND STORM RUNOFF TO THE SOUTH PLATTE RIVER IN THE SOUTHERN DENVER METROPOLITAN AREA, COLORADO By Steven R. Blakely, Martha H. Mustard, and John T. Doerfer ABSTRACT On August 14, 1980, an intense convective storm occurred over the Denver, Colo., metropolitan area. Urban runoff from this storm was monitored for both quantity and quality at three sites on the South Platte River and at one site on each of six major tributaries to the river. Tributary basins were analyzed and total areas, land use, and effective impervious areas were determined for compari¬ son with storm-runoff loads. The total measured rainfall ranged from 0.00 to 1.41 inches. The maximum 5-minute rainfall measured was 0.37 inch. Runoff loads were determined for total suspended solids, chemical oxygen demand, total organic carbon, and selected nutrients and trace elements. Runoff loads were calculated in pounds and pounds per acre per inch of rainfall. These loads also were computed as event mean concentrations, in milligrams per liter or in micrograms per liter, in storm runoff and in total runoff for comparison with State and Federal water-quality standards. The effect of storm runoff on the South Platte River was to increase the vol¬ ume of flow to nearly three times the base flow. The increase in main-stem runoff loads ranged from 2.6 times the baseload (total orthophosphate) to nearly 30 times the baseload (total suspended solids). The event mean concentrations of copper, lead, manganese, and zinc exceeded water-quality standards for aquatic life in Colorado at several sites monitored. The U.S. Environmental Protection Agency standards for brook trout were exceeded by copper and zinc at all sites monitored. Further analysis of storm-runoff-load data indicates that a significant part of the main-stem storm-runoff loads may be resuspended bottom material. Also, data are compared for a tributary basin with a flow-detention structure and a similar basin without a flow-detention structure. The runoff loads from the basin with the detention structure are significantly smaller than those from the basin with¬ out flow detention. INTRODUCTION Increasing public awareness of the possible degradation of the Nation's water resources resulted in studies to determine point sources of pollution during the 1970's. Particular emphasis was placed on identifying these sources and assessing their impact on rivers, streams, and lakes. As these sources were identified, attention focused on nonpoint sources of pollution. This resulted in the formation of a National Urban Runoff Program by the U.S. Environmental Protection Agency. 1 This program had the objective of assessing the impact of urban storm-water runoff on the water quality of receiving waters. The Environmental Protection Agency selected Denver, Colo, (among others) as a representative urban environment (in a semiarid climate) and provided grant monies to the Denver Regional Council of Gov¬ ernments to begin an impact assessment of urban storm-water runoff. Storm runoff can affect the quality of water in the South Platte River as a result of the trace elements and nutrients that accumulate in the environment. Little is known about the concentrations of these constituents in storm runoff to the South Platte River in Denver. Another unknown is the magnitude of nutrient and trace-metal loads that are suddenly introduced into the South Platte River by storm runoff. This effect could be significant, as the entire load is then rather quickly available to the aquatic life of the river. A study of the effect of storm runoff on the South Platte River was begun through a combined effort of the Denver Regional Council of Governments and the U.S. Geological Survey. The data presented in this report were collected as a part of this study. The storm of August 14, 1980, was selected for this report because it was the largest of only three storms in the Denver area during 1980 and 1981 that were of suffi¬ cient size and duration and that were monitored on an intensive basis. Purpose and Scope The purpose of this report is to present an analysis of the August 14, 1980, rainstorm in Denver, Colo., and describe its effects on the South Platte River and six of its tributaries (fig. 1). The analysis is separated into four parts: 1. Basin characteristics are presented and discussed for tributary and main- stem sites. 2. Rainfall quantities and intensities are discussed in terms of areal dis¬ tribution throughout the study area. 3. Basin characteristics, rainfall, runoff, and constituent loads are pre¬ sented in tabular format and discussed. 4. Total metal concentrations are compared with current (1981) State and Federal water-quality standards. Data-Collection Methods A network of rain gages (pi. 1) which previously had been established in the Denver metropolitan area was used to obtain 5-minute rainfall data. The Denver Regional Council of Governments, through a contract with the Urban Drainage and Flood Gontrol District, obtained radar-simulated rainfall data from GRD Weather Center, Inc., who generated the data using a mathematical model based on rain-gage and radar data. These simulated rainfall data have an areal resolution of about 1 square mile. Ground truth for calibration of the model was provided by rain-gage data. This information was used to obtain average basin rainfall quantities for the tributary basins and the main-stem basins. 2 Figure 1,—Location of water-quality and streamflow-monitoring stations and study area. 3 A data-collection network was established to provide streamflow and water- quality information at three main-stem stations on the South Platte River and six stations on its tributaries in the Denver area. The stage at the three main-stem stations was monitored by continuous stage recorders; stage-discharge relation¬ ships for these stations were derived using current-meter measurements, channel geometry, and indirect measurements of flow. Bear Creek and Cherry Creek were monitored by continuous stage recorders. Harvard Gulch was monitored by a continu¬ ous digital stage-recorder at 5-minute intervals. Stage-discharge relationships were derived for these stations as for the main-stem stations. The remaining three tributaries—Sanderson Gulch, Weir Gulch, and Lakewood Gulch—have nonrecording gages only, and stage data were obtained visually at intervals of 5 to 15 minutes by personnel onsite during the rainstorm. Stage-discharge rating curves for Sanderson Gulch, Weir Gulch, and Lakewood Gulch were developed using a step-backwater model (Shearman, 1976; Eichert, 1979) and were used to estimate discharge from stage observations at each of these sta¬ tions. Initial curves, developed using Shearman’s model, were verified against backwater interference using Eichert's HEC-2 step-backwater model. Runoff volumes were calculated for each station using the discharge data. The error inherent in computing discharges using stage-discharge curves derived by step-backwater meth¬ ods is estimated to be 10 to 15 percent for most of the sites (R. D. Jarrett, U.S. Geological Survey, oral commun., 1982). Base-flow volume was separated from the total runoff volume to provide storm-runoff volume. The error in storm runoff based on this subjective separation of stormflow and base flow from a continuous recorder strip chart is estimated to be as follows: Bear Creek, ±7 percent; Cherry Creek, ±35 percent; South Platte River at 19th Street, ±17 percent; and South Platte River at 50th Avenue, ±12 percent. Water-quality samples were collected at all stations in the stream!low-moni¬ toring network. Six to eight samples were collected at each station during the duration of the storm-runoff period. This sampling schedule was designed to insure that changes in the streamflow water quality as a result of storm runoff would be determined at several times during the storm. At each station an attempt was made to collect one initial sample of base flow, two samples during the period of in¬ creasing discharge, one or two samples at or about the peak discharge, two samples during the period of decreasing discharge, and a final sample as close to prestorm base flow as possible. Storm loads of selected constituents were calculated from the discharge and water-quality data. These water-quality data are published in a hydrologic-data report by Gibbs and Doerfer (1982). Tributary and main-stem drainage-basin boundaries were determined from topo¬ graphic maps and surveys of the area. The area for each basin was obtained, and boundaries were marked on a map of the study area (pi. 1). This map and aerial photographs were used to estimate land uses in seven categories (Turner, 1981) for each tributary and main-stem basin. This information was obtained for use in cal¬ culating impervious areas and to aid in the comparison of rainfall, storm runoff, and runoff loads from each basin. Topographic elevations from 7i$-minute quadrangle maps of the area were used to define surface-runoff basin boundaries. A comprehensive examination was not 4 made of the storm sewers that route runoff between basins, but the effects were assumed to offset one another. The size and frequency of basin interflows based on onsite observations indicate that this has minimal effect on total basin storm runoff. Storm-sewer maps did not exist for some areas of the metropolitan area (in particular, the west side of the South Platte River). Drainage areas were deline¬ ated from U.S. Geological Survey y^^-minute topographic maps at 1:24,000 scale. A map of the study area showing tributary and main-stem basins and monitoring sta¬ tions is shown on plate 2. Drainage areas for each of the monitored tributary and instream basins and for unmonitored areas are presented in table 1. Land use determined for the tributaries, main-stem basins, and unmonitored areas is presented in table 1, along with the percent of total area for the land use. Low-altitude black-and-white aerial photographs at an approximate scale of 1:12,000 were used as a base for interpreting land use. The photographs were taken during an overflight of the study area on May 31 and June 1, 1980. Land-use acre¬ age was measured to a resolution of 2.5 acres on a mylar base map placed over the aerial photographs. Definitions of each land-use category were taken from Turner (1981). The effective impervious area within each drainage area was calculated using the characteristic values for the Denver metropolitan area presented by Alley and Veenhuis (1979). The product of the mean percent impervious area and the mean per¬ cent of that impervious area, which is effective for each land-use category, was calculated to produce an average percent effective impervious area for each land use. This value multiplied by the number of acres in a basin for a particular land use produced the number of acres of effective impervious area from that land use in each basin. These values of effective impervious areas (acres) by land use were summed to provide a total effective impervious area for each basin and unmon¬ itored area (table 1). An average value of impervious areas and effective impervious areas reported by Alley and Veenhuis (1979) for industrial land was computed and used even though they did not report an average because the range of values was very large. The mean effective imperviousness of land in the single-family category was calculated to be 18 percent; in the multifamily category, 54 percent; in the commercial cate¬ gory, 86 percent; and in the industrial category, 39 percent. Lands in the park, vacant, and agricultural-use categories were assumed to have no effective imper¬ vious areas. The storm-runoff data and water-quality samples for five of the tributary sta¬ tions were collected by the U.S. Geological Survey and analyzed by the U.S. Geo¬ logical Survey's laboratory at Denver. Ambient and storm-runoff data and water- quality samples for main-stem stations and Cherry Creek were collected by the Den¬ ver Regional Council of Governments and analyzed by the Metropolitan Denver Sewage Disposal District No. 1 laboratory. Because analytical methods may differ from one laboratory to another and because two laboratories analyzed samples collected for this study, references are provided for the analytical methods used by each laboratory. 5 I y-N yp yAv yAs ’V 1 CO o aH in o CN 'd- OS sO CN A A A X) 1 r** f-H cn cn 00 o^ Os cn (Os cn 1 CN so CO 1 /-•s y^ /A\ yAs yAs 0) 3 1 v£> to cn cn OS CN m > 0 1 cn CN CN cn CN p CN cn CN •H iH CO 1 v—^ SA>r •.Ay NAy Sa^ NAy 'p SAy AJ > 0) 1 5 u u u I o CO o o O O o O o o A A A A A A A [i3 -H 1 CN aH ^H m o cn cn CO 1 ^H CN CN 1 y^ /— S y-N 1 o o o o o o o yAy o yAs 1 o o o o o o o OS O Os 1 ^H ^H aH aH OS OS CO ^ cO CO cu 1 1 Na^ Na/ >Ay Sa^ St XJ U 1 o o o o o o O O o o 0 CO 1 o o CN CTs o o o o o o • H 1 •.O' o r>. A A A A A A A A o 1 LTj CN <• o in cn sD P 00 u 1 Ip aH in O ♦P aH CO 1 p aH a rH <0 o 1 yp Sh iJ JJ 1 1 /-s y-N CN yAs yAs 0 rH 1 aH SO vO JJ TJ 1 'a^ >Ay Sa' T) O CO ) 0) CO •H J-i 1 CN o o o o o O o o X U 0 1 m p p Sh XJ 4J CkO XJ 1 in +i c:? 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CO 0 o d) 1 o O o in o o o O o o 0 c s 1 % 1 cn VO cn SO aH cn m in 1 CI- O ■H rH 1 'w' 'w' VAy 'Ay >Ay Sa^ sp Sa^ Sa^ d) X XJ XJ •H 1 p e 0) iH 6 1 o o 00 O O o o O GO -3 C 3 CO 1 CN so CN CN cn Os cn p >% 1 >—✓ 'a.' NAy NAy Nwy Sa^ Sa/ NAy Sa*' CD »H rH GO *H 1 1 O O o O O O o o O o d) C3 c i 1 On m 00 cn o o cn o X 1 •H 3 1 CN CN os O so OS Os CN p p 1 CO PJ 1 A A A A A A A A A 1 m AH CN CN in Nf SO 00 in CO 1 ^H m dr p 0) CO iH 1 1 1 I 1 1 1 1 o X i ' > p 1 > dj •H 1 1 X fH o 1 0) 1 •H D X fti C 1 o 3 J iH X 1 oc d) 1 . cc C d) 0 i iH O 0 0) no 1 p 5 » 0) N P XJ 0) 0) O c u P P - CO •-H 1 p < c XJ X p d) p o P p d) p in AH X CO P c •H X 0) B CO P CO X XJ p d) CO CO d) CO X C p p •H XJ p 3 CO CQ rc CO 3 HI u X a CO Q 3 to O , 0 O CO 1 CO CO 6 The method used by the U.S. Geological Survey’s laboratory for determining the total metals concentrations in water samples from Bear Creek, Harvard Gulch, Lakewood Gulch, Sanderson Gulch, and Weir Gulch was the "total recoverable" method as described in Skougstad and others (1979). Methods used to analyze samples from Cherry Creek and the main-stem sites were for "total" metals as described by the U.S. Environmental Protection Agency (1974) or by the American Public Health Asso¬ ciation (1980). Rain-gage data and stream-discharge data for all sites except Bear Creek and the South Platte River at 19th Street were provided by the U.S. Geological Survey. Streamflow data for these two sites were provided by the State Engineer of Colo¬ rado. Basin-characteristics data were provided by the Denver Regional Council of Governments. Description of Study Area The study area (fig. 1) is almost entirely within the Denver metropolitan area. It is defined by a reach of the South Platte River and its corresponding drainage area between two U.S. Geological Survey water-quality and streamflow¬ monitoring stations. Station 06710000 (South Platte River at Littleton) is on the upstream boundary of the study area, and station 06714130 (South Platte River at 50th Avenue, at Denver) is on the downstream boundary. The study area extends a maximum of 23 miles in a south-to-north direction, which is also the approximate direction of flow of the South Platte River through most of Denver. The maximum breadth of the study area is about 21 miles east to west. The altitude of the study area above sea level (National Geodetic Vertical Datum of 1929) ranges from about 7,965 feet in the foothills at the western bound¬ ary and from about 6,580 feet in the High Plains at the eastern boundary to about 5,140 feet at the 50th Avenue monitoring station on the South Platte River. The altitude at the Littleton monitoring station is 5,304 feet above sea level. The South Platte River in Denver flows within a broad alluvial flood plain situated within a piedmont basin at the edge of the Rocky Mountains. The channel bottom is mostly sand and gravel except for a few areas in which bedrock is ex¬ posed or sediment has accumulated. The length of the South Platte River between Littleton and 50th Avenue is about 15 river miles and is almost 12 miles by line- of-sight. The study area encompasses about 120,000 acres and is approximately 62 percent urbanized. The six major tributary basins monitored in the area range in size from 2,000 to 15,800 acres, and urban development ranges from 48 to 90 percent (table 1) of their individual areas. Land uses which are considered urban are single-family residential, multifamily residential, commercial, and industrial. The remaining land-use designations not considered "urban" in terms of storm run¬ off are park, vacant, and agricultural lands. 7 MONITORING STATION AND BASIN DESCRIPTIONS The tributary monitoring stations were located as close as possible to the mouths of the tributaries. The main-stem stations were located at existing stream- flow- monitoring stations, except for the South Platte River at 50th Avenue station which was constructed for this study. Two major tributaries. Big Dry Creek and Little Dry Creek, were excluded from monitoring because of several interbasin di¬ versions. Big Dry Creek and Little Dry Creek have total drainage areas of 12,100 acres and 11,500 acres, respectively, and together comprise 20 percent of the study area. 06710000 South Platte River at Littleton The South Platte River at Littleton stream!low-gaging station is the upstream boundary of the study area; therefore, the total drainage-area and land-use values upstream from the gaging station are not given in table 1. Streamflow in the South Platte River in the Denver area is regulated primarily by the Chatfield Lake dam, which is approximately 5 river miles upstream from this station. Any storm runoff occurring upstream from Chatfield Lake dam would be retained in the lake and diluted, thus not affecting streamflow. The area between Chatfield Lake dam and the Littleton stream!low-gaging station could contribute a significant quantity of storm runoff during a storm. Any storm runoff at this site would be subtracted from downstream runoff values to compute net runoff from the study area for those sites. There is a continuous-recording stage monitor at this station. 06711500 Bear Creek at mouth, at Sheridan The Bear Creek basin contains 15,400 acres between Mount Carbon Dam (locally known as Bear Creek Dam) and the stream!low-gaging station which is approximately 1.3 miles upstream from the mouth, at the town of Sheridan. The drainage area upstream from Mount Carbon Dam was considered to have an insignificant effect on urban-storm runoff because of retention in Bear Creek Lake. There is a continuous- recording stage monitor at this station. 06711575 Harvard Gulch at Harvard Park, at Denver The Harvard Gulch contributing drainage basin contains 2,000 acres between the Highline Canal (which intercepts runoff from the entire eastern part of the Harvard Gulch drainage basin) and the Harvard Gulch stream!low-gaging station at Harvard Park. This station is located about 1 mile upstream from the mouth. There is a continuous-recording stage monitor at this station. 06711610 Sanderson Gulch at mouth, at Denver The Sanderson Gulch basin contains 4,720 acres between the headwater divide and the monitoring site near the mouth of Sanderson Gulch. There is a nonrecording gage at this station. 8 06711622 Weir Gulch at mouth, at Denver Weir Gulch basin contains 4,790 acres between the headwater divide and the monitoring station near the mouth of Weir Gulch. About 0.75 mile upstream from the mouth, Weir Gulch flows through Barnum Lake, an approximately 7.4-acre flood- control lake usually 4 feet or less deep. There is a nonrecording gage at this station. 06711800 Lakewood Gulch at mouth, at Denver The Lakewood Gulch basin contains 10,400 acres between the headwater divide and the monitoring station near the mouth of Lakewood Gulch. There is a nonrecord¬ ing gage at this station. 06713500 Cherry Creek at mouth, at Denver The Cherry Creek basin contains 15,800 acres between Cherry Creek Dam and the Cherry Creek stream!low-gaging station 0.5 mile upstream from the mouth in down¬ town Denver. An unknown but probably substantial part (possibly 50 percent) of the runoff from the area east of the Highline Canal in the Cherry Creek basin is in¬ tercepted by the canal. Therefore, the contributing drainage area of Cherry Creek basin is unknown, but is something less than 15,800 acres. The data shown in tables 1 and 2 for Cherry Creek basin are based on an earlier assumption that the basin was unaffected by the canal. This information is presented only for compar¬ ison with other basins. The drainage area upstream from Cherry Creek Dam was con¬ sidered to have no effect on urban storm runoff discharged to the South Platte River by Cherry Creek because there is no outflow released from Cherry Creek Dam. There is a continuous-recording stage monitor at this station. 06714000 South Platte River at 19th Street, at Denver The South Platte River basin at 19th Street drains an area of 107,400 acres between the stream!low-gaging station at Littleton and the stream!low-gaging sta¬ tion at 19th Street in Denver. This basin contains all of the tributary basins and 54,300 acres of unmonitored area. There is a continuous-recording stage monitor at this station. 06714130 South Platte River at 50th Avenue, at Denver The South Platte River basin at 50th Avenue drains an area of 118,000 acres between the stream!low-gaging station at Littleton and the stream!low-gaging sta¬ tion at 50th Avenue in Denver. The area between the 19th Street station and the 50th Avenue station is 11,600 acres. Runoff from this area is considered direct flow and is monitored only as the difference between the streamflow at 19th Street and the streamflow at 50th Avenue. There is a continuous-recording stage monitor at this station. 9 PRECIPITATION On the afternoon of August 14, 1980, an intense convective rainstorm occurred in the Denver area, followed closely by an overnight upslope rainstorm. These storms were preceded by 4 to 6 weeks during which less than 0.15 inch of rainfall was recorded in the study area on any 1 day. The convective storm consisted of several very intense storm cells moving across the study area (pi. 3), which produced significant runoff at the monitoring stations (pi. 2). The convective storm was characterized by significant rainfall intensities throughout a large area (pi. 4). This was the first such storm for which water-quality data were collected for the National Urban Runoff Program from major urban tributaries to the South Platte River in the Denver metropolitan area. The upslope storm which immediately followed the convective storm lasted through the next afternoon. The areal coverage of the upslope storm was fairly uniform but the 24-hour rainfall was relatively small, ranging from about 0.2 to 0.5 inch. The runoff from the upslope storm was not monitored for three reasons: (1) The storm runoff is difficult to distinguish from the base flow when the peak discharge is small and the discharge is relatively uniform as would be expected from an upslope storm, (2) the storm-runoff loads from this particular upslope storm would not be representative of other upslope storms because the preceding convective storm had just removed much of the potential load from the basins, and (3) it is prohibitively expensive to manually monitor the runoff and water quality for more than a few hours. The rainfall was recorded using five tipping-bucket rain gages and eighteen 3-inch pipe totalizing continuous-recording (5-minute intervals) rain gages. Pre¬ cipitation graphs, rainfall-data summaries, and location of each of the rain gages are shown on plate 1. The total rainfall measured ranged from 0.00 to 1.41 inches. The duration of rainfall ranged from 0 to 150 minutes. The maximum measured 5- minute rainfall was 0.37 inch. The maximum 15-minute rainfall was 0.8 inch, and the maximum 60-minute rainfall was 1.41 inches. GRD Weather Center, Inc., indirectly monitored the storm by recording images of radar reflection over the study area from the National Weather Service’s Limon, Colo., radar transmitter transmitting at an angle of 0.5 from horizontal. The in¬ tensity of reflection of a microwave radar beam directed at a cloud is related to the size of the raindrops in the cloud which, in turn, is an indirect measure of the intensity of rain falling from the cloud (Linsley and others, 1975). Six discrete values were used to describe the entire range of radar- reflectivity intensities and, thus, to simulate areal rainfall intensities. A dis¬ crete value was recorded every 15 minutes as an areal average for each pixel, the smallest division of the radar-reflectivity map, representing approximately 1 square mile. The recorded values are temporal averages of three sequential 5- minute values. Using an exponential curve, CRD Weather Center, Inc., made a re¬ gression analysis of these radar-reflectivity values using recorded rain-gage data to produce maps showing the simulated rainfall in each pixel for each of 12 conse¬ cutive 15-minute time increments between 1330 and 1630 hours on August 14, 1980. 10 Precipitation maps based on the simulated rainfall during the most intense rain¬ fall periods (1400-1530 hours) are presented on plate 3. The 15-minute simulated quantities of rainfall from 1330 to 1630 hours were summed to produce a precipita¬ tion map for the entire storm (pi. 4) and to determine average basin rainfall (pl. 2). Both rain-gage and radar-reflectivity data are considered essential by the authors to characterize this storm. The rain-gage data are necessary to determine accurate rainfall quantities and intensities at specific locations; however, rain- gage data alone can be misinterpreted. The Thiessen method (Linsley and others, 1975), which is one of the most common means of extrapolating point-rainfall data to an average basin rainfall, depends on linear interpolation of the data points. However, the areal variability of rainfall is not necessarily linear, especially for a convective storm such as the storm of August 14, 1980, in Denver, Colo. The following is an example of the error involved in interpolating rain-gage data from Thiessen polygons. The calculated rainfall for Weir Gulch basin would have been 0.93 inch using the Thiessen method, whereas the basin rainfall was 0.28 inch using the more representative simulated-rainfall data derived from the radar and rain-gage data. Rainfall computed using the Thiessen method is weighted very heavily by data from the Villa Italia rain gage (pl. 1). This rain gage recorded more than twice as much rain as did any gage within 3 miles. Therefore, it is in¬ appropriate to use data from the gage to calculate rainfall for as large an area as indicated by the Thiessen polygon. This logic is supported by the areal vari¬ ability of rainfall shown by the radar data. Thus, the use of the Thiessen method alone will not provide sufficiently accurate resolution of rainfall information. Analysis of rainfall information can be significantly enhanced by the use of radar-generated rainfall data. The average basin rainfall determined for each basin from Thiessen polygons and from radar-simulation methods is compared in table 2. The addition of radar data provides a better estimate of the areal dis¬ tribution of rainfall than rain-gage data alone. Linear interpolation is not necessary because radar data of sufficient resolution for this study are recorded on a uniform grid. Furthermore, the value of each pixel is an average value of all the data within each pixel, not just the value of a single point within the pixel. There are some disadvantages in using radar data. One is that radar data are not sufficient to determine rainfall directly because there is no universal factor that can be applied to the radar data to convert them to rainfall data. The radar- rainfall data relationship needs to be determined for each storm. Another disad¬ vantage is that there are spatial and temporal differences between the rain fall¬ ing from the cloud as determined by radar and the rain measured at the ground (Linsley and others, 1975). These differences are considered negligible in this report. A third disadvantage of using recorded radar reflectivity in this manner is that the values assumed to represent a temporal average of three sequential 5- minute values may be in error when normal scanning is interrupted. During the August 14, 1980, storm, the National Weather Service used the Limon transmitter to 11 Table 2.— Comparison of average basin rainfall for the storm of ■ August 14^ 1980 3 for trihutai^y and main-stem basins as determined by the Thiessen polygon method and the radar-simulation method [Rainfall in inches] Thiessen Radar- Basin polygon simulation method method Bear Creek- Harvard Gulch- Sanderson Gulch- Weir Gulch- Lakewood Gulch- Cherry Creek- South Platte River at 19th Street— South Platte River at 50th Avenue— 0.33 .69 .39 .93 .54 .53 .59 .56 0.31 .33 .32 .28 .22 .29 .27 .27 scan the clouds for hail and tornadoes. This was done by altering the angle of transmission. Reflectivity values recorded during this process were eliminated from the data base; however, GRD Weather Center, Inc., always assumed there were three values to be averaged in the data-management system. Therefore, the average radar-reflectivity values were probably underestimated. For the purposes of this report, such errors were assumed to be negligible. BASIN CHARACTERISTICS, RUNOFF, AND RUNOFF LOADS Total area, effective impervious area, rainfall, total runoff, storm runoff, and the storm runoff-rainfall ratio for each of the monitored tributaries and for the 19th Street and 50th Avenue main-stem stations are presented in table 3. The rainfall data given for each basin are considered representative of the rainfall which occurred in that basin. The runoff volumes and the runoff-rainfall ratios are believed to be representative of the storm conditions of August 14, 1980, for Harvard Gulch, Bear Creek, Sanderson Gulch, and the 19th Street and 50th Avenue stations. All tables of runoff and of storm loads are presented in the order of increasing total area rather than in downstream order to aid in data comparisons based on basin characteristics. All runoff and load values given for the main-stem stations were computed by subtracting values observed at the South Platte River at Littleton station unless the difference was negligible or within the range of systematic and rounding error (±5 percent). 12 Table 3. —Total area^ effective impervious area, rainfall3 total runoffs storm runoff_ and runoff-rainfall ratios for tributary and main-stem stations from the storm of August 143 1980 [Runoff in inches is normalized to total basin area; rainfall is the radar-simulated rainfall basin average] u QJ > •H On >^CM CM CM CM 0 • • • • Vj Q) 0 0 UO 'cr UO QJ QJ 0 0 CM CM X M 00 CO 0 0 UO CU QJ V4 CO 0) PQ TO O ' o x: 5 o 0) rH X 3 CO O X U X •H O QJ r—I :2 a o d o CID X u o QJ rH TO 3 C O CO CO TO u CO > o rH 3 CO O X CM OD CX) o o o o o o <}■ ► r'. CM CO CM O X On CO CO CO CM O p'* o o o Mj- X o o o uo CO CM CM CM CM X CM C7D CO CO o o <3- m o X <0- CM X o 'O’ CM 00 'O’ o uO CM CM 00 X 'O’ X O o o Mr o o -O’ CO CO CO P'. P'' 00 CM (0^ o^ CM cn CO uo o o CTN o ON o CO CM <3^ CM CO CO UO p'' O O CM P'' O p'. m CM CO CM CO CO CM CM m X o o o CM 00 CM X CO o UO 1 1 1 1 /—s 1 X /-N 1 CO 1 cn 1 1 u-t X X X X 1 X QJ X 1 3 1 3 1 -l cC 1 0 1 0 4J 0 d QJ 0 d QJ 0 0 1—1 0 ) QJ cQ 0 QJ QJ •H QJ •H c CD M 0 X d 0 X d CD d X CD CD 0 4-) W) J-i CE > > OD > > QJ r—i QJ 3 X 3 *H 3 QJ 3 CO QJ CD X CQ QJ CC QJ •H QJ •H CJ X X U X CJ X rH 0 X X X X 0 X QJ QJ Q 4J U 4-1 QJ CO U 4J QJ CO M CO 0 X X fH X CJ d X CJ X X a. CQ rH 0 CJ CX QJ U CJ 0 - QJ QJ IM d X X X a •H X a d a X X d CJ O. a CO CO QJ E U CO QJ a U CX C •H CO a 3 X B 3 X X X CO CO X d X CD 4-1 CM •H CO CM •H CO •H X v-x 0 0 o 0 'w' 0 X X X QJ cO 0 CM iM CO 0 X X X H w w X H CO CO CO QJ QJ 0) 0) CO CO r-H Csl 13 discussion of Lakewood Gulch data discussion of Cherry Creek data. Data presented for Cherry Creek are qualified by the effect of the Highline Canal, an irrigation canal which traverses Harvard Gulch and Cherry Creek in a northeasterly direction (pi. 1). At the beginning of the project it was assumed that the Highline Canal had no effect on the volume of storm runoff occurring in the basins it traversed. However, recent visual inspection reveals that it inter¬ cepts runoff from the entire eastern part of Harvard Gulch basin and a large pro¬ portion of the eastern part of Gherry Creek basin. The Harvard Gulch data were revised, but an exact determination of the effect in Gherry Greek basin would require an engineering survey which is beyond the scope of this project. The Gherry Greek data on runoff volumes and storm loads are accurate to the extent that they show what Gherry Greek delivered to the South Platte River at the mouth on August 14, 1980. The information shown in tables 1 and 3 regarding con¬ tributing drainage area (total area) for Gherry Greek basin is too large by an un¬ determined area. The information regarding storm runoff (and runoff in inches) may be less than the actual values by as much as 27 percent or 1.55 million cubic feet of storm runoff. As much as one-half and possibly more (R. L. Rosendale, Highline Canal Ditch Superintendent, Denver Water Board, oral commun., 1982) depending on the storm intensity of the storm runoff in Cherry Creek basin east of the canal is intercepted and transported out of the basin by the canal. The area in Cherry Creek basin east of the canal is 54 percent of the total Cherry Creek area. Thus, it is estimated that at least 27 percent of the storm runoff and possibly more is transported out of the Cherry Creek basin by the Highline Canal. The uncertainty involved in evaluating the magnitude of Cherry Creek storm runoff and loads with regard to total and effective impervious area precludes mak¬ ing any conclusive statements of comparison with other basins. It is apparent that the values given for total and effective impervious area for Cherry Creek basin downstream from Cherry Creek Dam (54 percent of which is east of the Highline Canal) are large due to the known but unquantified effect on these areas of the Highline Canal, and further that the values given for rainfall and runoff, in inches, are therefore of limited value. Any subsequent discussion and comparison, of runoff and loads involving Cherry Creek data need to be considered with this qualification in mind. There also are qualifications to the runoff volumes and runoff-rainfall ratios shown in table 3 for Weir and Lakewood Gulches because flow in the gulches may have been detained. Storm hydrographs for each monitored tributary and for the main-stem stations are presented in downstream order in figures 2, 3, and 4 to evaluate temporal and geographic effects on loading. A graph of total suspended-solids load for each station is presented with the hydrograph for a comparison of loads for the tribu¬ tary and main-stem stations. Harvard Gulch received the greatest rainfall (0.33 inch) and delivered the greatest unit storm runoff (0.165 inch). Sanderson Gulch received the next great¬ est rainfall (0.32 inch) and delivered the next greatest unit runoff of the tribu¬ taries monitored (0.075 inch). Weir Gulch received almost the same rainfall (0.28 inch) as did Gherry Creek (0.29 inch), but the runoff from Weir Gulch was only 0.053 inch compared with 0.073 inch from Cherry Creek—a comparison qualified by the earlier discussion on Cherry Creek. This may have been due to the detention effect of Barnum Lake and possibly to the relatively small effective impervious 14 DISCHARGE, IN CUBIC FEET PER SECOND Figure 2.--Discharge and loads of total suspended solids versus time at Bear Creek, Harvard Gulch, and Sanderson Gulch during the storm of August 14, 1980. 15 TOTAL SUSPENDED SOLIDS, IN POUNDS PER SECOND xIO Figure 3,—Discharge and loads of total suspended solids versus time at Weir Gulch, Lakewood Gulch and Cherry Creek during the storm of August 14, 1980. 16 TOTAL SUSPENDED SOLIDS, IN POUNDS PER SECOND x 10 DISCHARGE, IN CUBIC FEET PER SECOND TIME, IN HOURS Figure 4.—Discharge and loads of total suspended solids versus time at the main stem stations: South Platte River at Littleton, South Platte River at 19th Street, and South Platte River at 50th Avenue during the storm of August 14, 1980. 17 TOTAL SUSPENDED SOLIDS, IN POUNDS PER SECOND xIO area in Weir Gulch. The hydrograph of the storm runoff for Weir Gulch (fig. 3) is more attenuated than the hydrographs for other tributaries. It is low and rela¬ tively flat, a characteristic of streams controlled by flow-detention structures. The hydrograph for Lakewood Gulch (fig. 3) shows the discharge for Lakewood Gulch did not return to base-flow levels during the monitoring period. Therefore, the total runoff and storm runoff given for Lakewood Gulch is not considered rep¬ resentative of the total storm data for this site. Judging from the hydrograph (fig. 3) and runoff in inches (table 3) for Lakewood Gulch, there seems to be an unknown source of detention of flow in Lakewood Gulch. An estimated 1.6 million cubic feet of storm runoff for Lakewood Gulch was calculated using an average of the runoff/rainfall ratios for the other three tributary basins on the west side of the study area [(1.6 million cubic feet = 0.19 (inches of runoff)/(inches of rain) X 0.22 (inch of rain) X 10,400 (acres) X 3,630 cubic feet per acre-inch)]. This is 2.5 times the value shown in table 3 which was calculated from the hydro¬ graph shown in figure 3. The value in table 3 is provided only for comparison with other tributary data as an indication of the minimum magnitude of runoff in Lakewood Gulch. Runoff from the Bear Creek basin was least (0.048 inch), even though it re¬ ceived the third greatest rainfall (0.31 inch); this probably is due to the small effective impervious area in the basin (16 percent). Rainfall for the South Platte River at 19th Street basin and the South Platte River at 50th Avenue basin was the same (0.27 inch), but the runoff was significantly different (0.070 and 0.089 inch, respectively). This is due to the relatively large percentage of direct-flow storm runoff entering the South Platte River between the 19th Street and the 50th Avenue gages (31 percent), compared with the percentage of drainage area (9.7 per¬ cent) between the 19th Street and the 50th Avenue gages. This large volume of run¬ off probably is related to the large effective impervious area (34 percent) in the drainage area between the 19th Street and the 50th Avenue gages. The runoff-to-rainfall ratio for this storm (table 3) expressed as percent appears to be similar to the percent effective impervious area for the Bear Creek, Sanderson Gulch, and Cherry Creek basins. The differences are less than 2 percent. This relationship is within 4 percent for Weir Gulch and for the 19th Street sta¬ tion. However, it may only be fortuitous that these values are so similar. The relationship is not as similar for the Harvard Gulch station or the 50th Avenue station where the percent runoff/rainfall substantially exceeds the percent effec¬ tive impervious area (50 percent versus 31 percent and 33 percent versus 23 per¬ cent, respectively). This probably is due to the unusually large direct flow to the South Platte River downstream from the 19th Street gage discussed earlier and the possible error inherent in computing an effective impervious area for an area which has the greatest percentage of industrial land use. This could easily account for an underestimated effective impervious area from 19th Street to 50th Avenue. Some additional error in runoff values may have been introduced from the subjective separation of the 50th Avenue hydrograph into its base-flow and storm- flow components. 18 There also is a possibility that main-stem flow may have been significantly increased by inflow of approximately 200 and 100 cubic feet per second of storm runoff spilled into Big and Little Dry Creeks, respectively (R. L. Rosendale, Highline Canal Ditch Superintendent, Denver Water Board, oral commun., 1982), from the Highline Canal during the storm. The total volume of this inflow is estimated to be as much as 4.1 million cubic feet (94 acre-feet; 10.5 percent of the storm runoff at the 50th Avenue gage). When the capacity of the canal is exceeded, or when the canal contains no water (which was the case on August 14, 1980), a gate is opened and the excess water flows into Big and Little Dry Creeks, both of which are located in one of the unmonitored areas in this study. Storm-runoff loads of the tributaries shown in table 4 were calculated using constituent concentrations and storm runoff. Therefore, the values of the storm loads shown for Weir and Lakewood Gulches and Cherry Creek are subject to the same qualifications noted earlier for the runoff volumes for those stations. Table 4.— Storm-runoff toads for tributaries monitored during the storm of August 14^ 1980 [Loads in pounds] Constituent Harvard Gulch Sanderson Gulch Weir Gulch^ Lakewood Gulch^ Bear Greek Cherry Creek^ Total suspended solids- 32,000 140,000 52,000 59,000 120,000 1,400,000 Chemical oxygen demand- 11,000 26,000 10,000 14,000 22,000 120,000 Total organic carbon- 2,300 6,000 3,000 3,400 7,200 41,000 Total nitrogen- 300 810 320 240 680 2,800 Total Kjeldahl nitrogen- 280 770 280 210 500 2,800 Total phosphorus— 37 170 55 78 130 1,100 Total orthosphate- 11 12 4.2 4.5 18 42 Total copper- 2.0 10 5.1 9.2 8.2 90 Total lead- 25 75 31 26 51 300 Total manganese- 44 170 78 89 120 650 Total zinc- 20 61 30 38 68 440 ^See discussion of Weir Gulch data. See discussion of Lakewood Gulch data. ^See discussion of Cherry Creek data. 19 Sanderson Gulch transported a suspended-solids load almost three times that of Weir Gulch, which is nearly equivalent in total area and effective impervious area. All the constituent loads in Sanderson Gulch were about two to three times the load computed for Weir Gulch. This comparison and the attenuated storm-runoff peak for Weir Gulch (fig. 3) indicate that Barnum Lake has considerable effect on the runoff load from Weir Gulch. If an estimated runoff of 1.6 million cubic feet were used to compute the suspended-solids load of Lakewood Gulch, the estimated load would be 148,000 pounds, or about 2.5 times the value in table 4. This estimated load represents an approximate upper limit for the suspended-solids load of Lakewood Gulch during this storm. Of the tributaries. Cherry Creek had the greatest total and constituent loads. Loads from Cherry Creek ranged from 2.3 to more than 10 times the loads computed for either Sanderson Gulch or Bear Creek. Cherry Creek basin is only slightly larger than Bear Creek basin, but has 1.75 times the effective impervious area if one disregards the unmeasured effect of the Highline Canal mentioned ear¬ lier. The Cherry Creek basin is 3.35 times larger than the Sanderson Gulch basin and has 3.7 times the impervious area. The last two comments regarding Cherry Creek are an understatement of the probable relationship for Cherry Creek basin statistics and are included here only to provide an illustration of the "natural" basin comparisons. The effect of the Highline Canal actually makes the comparison with other basins even more extreme. The relatively large loads in Cherry Creek probably are the result of exten¬ sive channel modification, which was in progress during the summer of 1980. The storm-runoff quantity from Cherry Creek is representative of a smaller area than originally believed, and the storm loads presented are believed to have been greater than what normally would have been computed for Cherry Creek. The loads computed for Harvard Gulch, Sanderson Gulch, and Bear Creek are believed to be representative for those basins. Loads shown for Weir Gulch and Lakewood Gulch probably are less than actual loads for the reasons discussed earlier. Cherry Creek loads which represent a smaller area than originally thought are believed to be greater than what the undisturbed basin and channel usually would deliver from a storm of this magnitude. Storm-runoff loads, normalized to inches of rainfall and total area for tribu¬ tary and main-stem stations, are shown in table 5. It was hoped that this analy¬ sis of the data would decrease the great variability in loads between basins. The limitations on loads because of qualified runoff quantities stated earlier are still obvious here. However, an average of the five tributary values (excluding Lakewood Gulch) for total lead (0.038 pound per acre-inch of rain) is quite simi¬ lar to the values for the South Platte River at 19th Street and the South Platte River at 50th Avenue (0.038 and 0.039 pound per acre-inch). Other constituents have a much greater range of values, and this comparison may be subject to greater differences. Given the qualifications stated earlier for Weir Gulch, Lakewood Gulch, and Cherry Creek, the loads presented in table 5 indicate the relative magnitude of loads that could be expected from a similar storm in areas of similar size, climate, and land use. 20 Table 5. —Normalised storm-runoff loads for tributary and main-stem stations on the South Flatte River for the storm of August 14, 1980 [Storm-runoff loads are normalized to inches of rainfall and total area; units are pounds per acre-inch of rainfall] >-i cu > •H CU 4J J-J cC iH Pu O in (U CTv Cd^ o x: d O CXd r—1 CO 'd' VO ■U 4_1 d X O Cd^ (N o o CO t-H o C o (U • m > O t—I CM CN CNJ 4-) CN t-H CO Xi a) ^ro cjv o vO U M CN O CN vO CTv M OJ o VD X CN o O o r-^ O 1—1 d cu in X o cu CJ d rH X u Td d o u jd VO r'. CO CT\ CdV 1-H CO o Cd o 140 CN LO o CO VO CO 2 d '-1 140 •H 0) JJ 3 O CO vO 00 cs CU • • X 3 o O o CO CN CO o o o o JJ u 3 o o H COV o o <3 O CU cr\ cn UO CTv 00 m > #s < CM CTv o • • x: CU o o o CM f-H 'O’ o o o o J~> -u cu o 'O’ o CJv "O’ o VO <3 m CO VO CM ov 4J CO CO CM vD CO u ^ • • M 0) o o o r—^ o o o o 0) 0) o m vD csi o o O x: u CM -O’ CO CM 'O’ VO u u 0S m CM o u ^ o o 00 CO cu • • • • 0 ) cu o o 00 'O’ CO O o O o CQ U CT^ CO •^r UO o 'O’ CM CJ) vD CO p'. 'O’ T) f-H O' CO co^ o x: • • • • o O o m sD UO O o o o cu tH O \D 00 CM VO o vO 3 m CO CM VO CM OS CO O 9s 9s hJ CM VO 00 SO o C7V o M xi • • • • •H O O m m O O O O CU iH 00 UO o 'O’ O t—H 12 3 UO “O’ UO CJ3 9s 3 •O’ O so CD xi • • • M CJ o o 'O’ o c^^ CM o O O O (U iH o CO CO CO o UO *3 3 CO crv O' C •s 9s CO CM CO TJ T'H VO CM 00 m CO O * • • • > iH \D vD CNJ 'O’ ro o o O O 3 •vT m CO CO UO p'' CO CL2 'O’ CO VO CM X 1 1 1 1 3 1 1 1 1 1 1 1 1 3 1 1 1 1 1 1 1 1 1 1 1 1 O 1 1 1 1 4J 1 1 1 1 1 1 X) 1 1 1 1 3 1 X 1 1 1 1 1 u 1 1 1 43 1 '' — 1 o 1 1 3 1 1 Xt 3 1 CU 1 00 X 1 X 3 03 3 ^ o 1 1 3 1 3 1 3. 3 1 0) iJ < 4-1 CO rH 04 cn -d- CM 00 CM JZ XJ • • • • 4J s: a> o o On 00 CM o O o o 3 4J 4J 0) o -d" cn -d- o -d- o < o\ u -O’ CN -d- m so in XJ #s •N cn CSI m cn 00 CM • • • >-l 0) O O o O sr -d" CON u m CM m CM T3 O ' -d’ cn o^ o x: • • • • 5 a o o CM so m o O o o 0/ I—i o -d" 00 CM o o ^ 3 m CM NO CTN CO O r—H CM in m o O 1-1 x: • • • • •H o O o vO m O o o o CU iH cn as in ON n- o m 3 a^ m 00 m o 3 sT O cn CO X • • • u a o o ro O Os CM o O o o D I—1 o CM CM 00 o CM 'O 3 cn 00 o r>. 3 O 0i 3 CM in 33 CM 00 1-1 J 00 m 1-H 3 O • • • • > r-t o o CM >-✓ 3 1 S-r •H 3 G X 3 1 O 1 33 a 1 O 1 3 3 1 XJ 3. Vw' o 3 1 3 1 rH 3 m 1 x 1 3- 33 00 1 o CD CD 00 1 XJ 1 3 3 o 1 XJ 1 a 3 3 1 3 3 3 w 1—1 33 iJ •H •r—) 00 j= H /~N o 3 3 /~v •H O 3 33 3 3 O 3 O 3- O hJ a rH 0 h4 N O ►H O 3 IJ 1—1 r—1 •H G r-l oo r—1 00 rH XJ rH 00 rH 00 rH r-l iH oo rH 3 0 G 3 3 6 3 3 •H 3 e 3 0 3 3 3 3 3 XJ w 3 33 XJ XJ XJ 3 XJ 'w' XJ s.^ XJ XJ 3 S-r XJ O JZ O O o O o O O O O H u H H H H H H H H H c o •H CO CD o CO •H 'C 0 ) (U c /0 27 of Lakewood data — 7.7 Lead- >7.8 Manganese- . 0 Zinc- >7.8 South Platte River at 19th Street Copper- >14.5 Lead- >15 Manganese- >13 Zinc- >14.8 South Platte River at 50th Avenue Copper- >18 Lead- >18 Manganese- >14.5 Zinc- >18 Table 11.— Speoifio oonduotanoe and pH in storm-runoff samples oolleoted during the storm of August 24, 1980 [Values were determined in the laboratory. ijmhos/cm=micromhos per centimeter at 25° Celsius. pH units were corrected to 25° Celsius] Station Specific conductance (ymhos/cm) pH (units) Number of samples collected Maximum Minimum Mean Maximum Minimum Mean South Platte River at Littleton^- 470 450 7.6 7.4 2 Bear Creek- 450 190 300 8.4 7.7 8.0 7 Harvard Gulch- 820 160 300 8.2 6.7 7.4 8 Sanderson Gulch— 810 160 400 9.0 7.8 8.4 7 Weir Gulch- 900 250 430 8.0 7.5 7.8 6 Lakewood Gulch- 930 240 460 8.6 7.8 8.2 7 Cherry Creek- 1,040 260 460 8.4 7.5 8.05 7 South Platte River at 19th Street- 610 330 430 7.9 7.1 7.5 7 South Platte River at 50th Avenue- 610 350 410 7.7 6.9 7.3 7 ^Mean and median values are not reported because only two samples were taken during the storm. 32 SUMMARY Storm runoff can be detrimental to the water quality of the South Platte River when trace elements and nutrients which have accumulated in the Denver metropolitan area are flushed into the river by storm runoff. The objective of this report was to assess the effect of urban storm runoff from a major rainstorm of large areal extent on the quality of water of the South Platte River in Denver, Colo. On the afternoon of August 14, 1980, an intense convective storm of broad areal coverage occurred in the Denver metropolitan area. Total measured rainfall ranged from 0.00 to 1.41 inches at 23 rain gages, the maximum duration of rainfall at any one rain gage was 2.5 hours, and the maximum 5-minute rainfall was 0.37 inch. The rainstorm was monitored by radar at 15-minute intervals. The rela¬ tionship between the radar data and the rain-gage data was used to obtain radar- simulated rainfall data for the entire study area. The radar-simulated rainfall data were used to prepare a precipitation map for the entire storm and individual precipitation maps for six consecutive 15-minute intervals of the most intense rainfall. The intensity of rainfall from this storm was so variable that rain-gage data alone could not provide adequate definition of the areal distribution of rainfall. The radar-simulated rainfall data provided the areal coverage and resolution necessary to obtain estimates of basin rainfall. However, rain-gage data were used to determine rainfall intensities and to provide known values of rainfall for cor¬ relation with the radar data. Urban runoff from this storm was monitored for quantity and quality at six major tributaries and at three main-stem stations on the South Platte River. Total areas, land use, and effective impervious areas were determined for compari¬ son with storm runoff and storm-runoff loads. The study area is a reach of the South Platte River between the Littleton and the 50th Avenue gaging stations and has a drainage area of nearly 120,000 acres. Forty-five percent of this study area was monitored for tributary storm runoff. Tributary basins range in size from 2,000 to 15,800 acres. Land use in the tribu¬ tary basins ranged from 37 to 72 percent residential (single family and multifam¬ ily) , from 11 to 25 percent commercial and industrial, and from 10 to 52 percent open space (park, vacant, and agricultural). Effective impervious area, which was calculated for each basin from land-use data, ranged from 16 to 33 percent of the tributary drainage area. Total loads and storm-runoff loads were determined for total suspended solids, chemical oxygen demand, total organic carbon, and selected nutrients and metals. Runoff loads were calculated in pounds and pounds per acre-inch of rainfall. Load data for storm runoff and total runoff also are presented as event mean concentra¬ tions, in milligrams per liter and micrograms per liter. 33 Storm runoff to the South Platte River increased the volume of flow at the 50th Avenue gaging station to nearly three times the base flow. The increase in main-stem storm-runoff loads was from 2.6 times the base-flow load (total ortho¬ phosphate) to nearly 30 times the base-flow load (total suspended solids). Total runoff from the tributaries ranged from 680,000 to 5.2 million cubic feet, and storm runoff ranged from 640,000 to 4.2 million cubic feet. Total runoff for the study area was 60 million cubic feet (approximately 1,400 acre-feet), and storm runoff was 39 million cubic feet (approximately 900 acre-feet). Storm-runoff loads also were computed for the tributaries. Total suspended solids ranged from 32,000 to 1.4 million pounds, chemical oxygen demand ranged from 10,000 to 120,000 pounds, total phosphorus ranged from 37 to 1,100 pounds, and total lead ranged from 25 to 300 pounds. Storm-runoff loads for the same con¬ stituents for the entire study area were 6.9 million pounds for total suspended solids, 840,000 pounds for chemical oxygen demand, 9,100 pounds for total phos¬ phorus, and 1,200 pounds for total lead. Additional nutrients and metals monitored include total organic carbon, total nitrite plus nitrate, total Kjeldahl nitrogen, total orthophosphate, total copper, total manganese, and total zinc (total nitro¬ gen was calculated by adding total Kjeldahl and total nitrite plus nitrate). At two stations monitored on the South Platte River, the event mean concen¬ trations of copper and zinc exceeded water-quality standards for aquatic life in effect in Colorado. Lead concentrations exceeded proposed standards for aquatic life at all stations, and manganese concentrations exceeded them at six stations. An analysis of cumulative tributary stormload versus main-stem stormloads indicates that a substantial part of the load in the South Platte River is resus¬ pended bottom material, if the unmonitored area can be assumed to contribute the same proportion of storm-runoff load as the monitored area. The magnitude of the constituent loads from possible bottom scour of the South Platte River based on data from the 19th Street gage in Denver could be as much as 40 percent of the total suspended solids, 50 percent of the total phosphorus, and 6 percent of the total lead. The analysis also indicates that a detention structure on a major tributary may significantly decrease storm-runoff loads. A comparison of storm-runoff loads from two adjacent tributaries, Sanderson Gulch and Weir Gulch, which have nearly equal total and effective impervious areas, seems to support this possibility. The basin with a detention structure had significantly smaller storm-runoff loads. 34 REFERENCES Alley, W. M., and Veenhuis, J. E., 1979, Determinations of basin characteristics for an urban distributed routing rainfall-runoff model, in Stormwater Manage¬ ment Model (SWMM) Users Group Meeting, Montreal, Canada, May 24-25, 1979, Proceedings: Washington, D.C., U.S. Environmental Protection Agency Miscel¬ laneous Reports Series EPA 600/9-79-026, 27 p. American Public Health Association, 1980, Standard methods for the examination of water and waste-water (15th ed.)* American Public Health Association, 1500 p. Colorado Water Quality Control Commission, Colorado Department of Health, 1979, Proposed water quality standards for Colorado: Denver, Colorado Department of Health, Draft No. 9, 38 p. _1981, Colorado code of regulations. Water quality standards and stream clas¬ sification (1002-8): Denver, Colorado Department of Health, v. 5, 99 p. Eichert, William, 1979 (revised 1981), HEC-2 step-backwater model: Davis, Calif., Hydrologic Engineering Center, 39 p., 8 appendices. Gibbs, J. W., and Doerfer, J. T., 1982, Hydrologic data for urban storm runoff in the Denver metropolitan area, Colorado: U.S. Geological Survey Open-File Report 82-872, 553 p. Linsley, R. K., Kohler, M. A., and Paulhus, J. L., 1975, Hydrology for engineers: New York, McGraw-Hill, 482 p. Shearman, J. 0., 1976, User’s manual, computer applications for step-backwater and floodway analyses: U.S. Geological Survey Open-File Report 76-499, 103 p. Skougstad, M. W., Fishman, M. J., Friedman, L. C., Erdmann, D. E., and Duncan, S. S., eds., 1979, Methods for determination of inorganic substances in water and fluvial sediments: U.S. Geological Survey Techniques of Water-Resources Investigations, Ghapter A1, Book 5, 626 p. Turner, J. E., 1981, Land use in the Denver metropolitan area: Denver Regional Council of Governments, 80 p. U.S. Environmental Protection Agency, 1974, Methods for chemical analysis of water and wastes: Washington, D.G., p. 82-83. _1976, Quality criteria for water: Washington, D.C., 256 p. 35 ☆ U. S. GOVERNMENT PRINTING OFFICE: 1984—778-999/9251 REGION NO. 8 ‘'’if 'i ■ - c tbrtu^ .._»i ?» f^7 ^■.;. * * .. | .‘ .. >* ^ • 4,J.#ii ‘tlii ‘if»» .At .ir#C -.,:**■* fjfc--. ( •H *r' :• ■“ * j JOi V ‘ .Mii ^ ;•>» *. *• •■ Cl# * .'0 iV<> . « i, ' , :jn *‘’ ' .1.*. : 'vi.,'* h 'IW \ .--V’ p'\ ’ •> ■ . - ' ■'' rf.'r j 4 T < < i-i w.ij. ■ '•i __ • ■ if ^ /;sv ■ ■•,?■ , , , ojn <'}^>v »’ ‘*o i-'J c*^'' H Zi ^ ' , V -‘ • -L': i . i0^ : i ' - * ** *- •-^ * 4-^1 'Oa*'- 1.'.*, *,..7^—»«* ^ * » g*' w •» UftCTlfc .i 1 > ‘g-. .iltl 4 f i . .*,*i** < ,flt ii.' __ , „ -y. I f. . _,• • :• *r'fj ; . .jk ' Jt !3J^s$ti? :> *•« -4*•I ftgi X..' IfV^J ■..'"^ i v'»(> *: n- J 4. t M*- ' • \ I ^ . » V < < .r*<. * > It ’ mi - .1 - » ‘ «r«< ^ nti , a 4^' ‘ *1 , • . . n u3|?- • 19 4 T-v*^ 1 ‘“V %l!' r . ''j 1 4P4M|.' ■ ' '■■•'^aA ■• .-’ll,;. ,. n.. i ' ^ ,_-ViVa«i4‘^-V;, •■r.fj*4d'Sl .,g,4a| -* .W . -yjin i-5‘ r4&r,^i4Lt ..-uer i y ^marnu 'v.’i' .,. ^*r, .T .fe*iv'4aP'y]ff ^ I‘ -f > t ^ . 1..J ■. 'V* ’ 3f- ■ ?* t»l f « , r ,0.4- - -. V ♦; ^*5 . Hr ^ * *i .-tf • • %- • il ■*■ *. fi. • J ‘ I >4'^ •aiul ' 4 • ♦■'•t » '•■:kn»r.,- » jJiM iv^sf. . . p : . IS. '-*',: iv^ &)|4 tiJUJttA:.' v . j. *4i.> 7 ,. '■ ii'l J -xa • r > ■ »UV c4jS V .rn " *'*V' o,.» . i«i« t • 1. 4 0, (* ' -a .r: • J , .‘I -r 0^' V. 4 '* '^- .'AiM* '"V•■•«*' *t«v Jt/ • . riar i f S3 - W i WATER-RESOURCES INVESTIGATIONS REPORT 83-41 PI ATF R.67 W. BUT ARY 1-T DAM$7t^_ lURS ER CO minutes 11 = 0.06 i nch all =0.14 inch aW=\0-20 inch E I L .J HARN'ARD GULCH AT BETHESDA ISSQO TlljyiE Total rainfal I p C Duration of r^n^a Maximum 5-minu ■Maximum 1 5-mir 1600 IN .HOURS 5^ inch l.f = 85 minutes t^rainfal I = 0.07 inch te rainfall = 0.16 inch te rainfal I = 0.42 inch 1400 06710000, T.3S. EXPLANATION NONCONTRIBUTING AREAS RAIN GAGE WATER-QUALITY STATION STREAMELOW-MONITORING STATION AND NUMBER 39“45' harvard gulch at BRADLEY SCHOOL,AT DENVER m' ^ 0 1400 T Lm. I- 1700 1500 1600 TIME, IN HOURS Total rainfal I = 0.68 inch Duration of rainfall =125 minutes Maximum 5-minute rainfal I = 0.1 3 inch Maximum 15-minute rainfal I = 0.31 inch Maximum 60-minute rainfal 1 = 0.58 inch HARVARD GULCH TRIBUTARY AT ENGLEWOOD AUXILIARY RAIN GAGE 1700 1500 1600 TIME, IN HOURS Total rainfal I = 0.61 inch Duration of rainfal I = 80 minutes Maximum 5-minute rainfall =0.10 inch Maximum 15-minute rainfal I = 0.27 inch Maximum 60-minute rainfal I = 0.57 inch T.66W. 104“45' CHERRY KNOLLS STORM DRAIN AT DENVER - 1 - 1 - 1 - 1 - 1 UNITED STATES DEPARTMENT OF THE INTERIOR GEOLOGICAL SURVEY Prepared in cooperation with the DENVER REGIONAL COUNCIL OF GOVERNMENTS 55/. ‘ff Uh ws3-<^/33' WATER-RESOURCES INVESTIGATIONS REPORT 83-4138 nPiY LIBRAP^ _ plate 1 105°15' _ R.70 W. nortIh avenue storm drain at DENVER FEDERAL CENTER NORTH AVENUE, AT LAKEWOOD . O I T i < 1 - - < X ^ 2 - T L. R,69 W, 105°OO' R.68W. AGRICU-TURAL DITCH INFLOW TO DENVER FEDERAL CENTER, AT , LAKEWO 3D MCINTYRE GULCH NO. 2 AT| DENVER FEDERAL CENTER, AT LAKEWOOD T 1 1700 T.3 S. 1400 1500 1600 TIME, IN HOURS Total rainfall =0.'! inch Duration of rainfall =20 minutes Maximum 5-minute rainfall = 0.03 Maximum 15-minute rainfal I = 0.07 Maximum 60-minute rainfalI = 0.10 DENVER FEDERAL CENTER FIELD AT LAKEWOOD -T 1 - 1 -r ~T 1 1 -1-1 ^ - -0=1= 3 -J YoO - -) ^2 2 <5^2 _ isli J 1 < cc. n 1 1 1 JL- 1600 1700 1400 1500 1600 J 1700 . IN HOURS TIME, IN HOURq 1400 1500 TIME Total ra nfall = 0.13 inch Duration of rainfal I = 20 minutes Maximum 5-minute rainfal I = 0.05 inch Maximum 15-minute rainfall^-^Tn inch \Maximum 60-minute raio-^^Tl = 0.13 inch Total rainfal I = 0.34 ^acb_. Duration of rainfall =t_30 mir utes - --- .. rai?ifall= 0.19 < X ± 2 39045 . T L T L ~r T “T 1400 1700 1500 1600 TIME. IN HOURS Total rainfal I = 0.47 inch Duration of rainfal I = 35 minutes _ Maximum 5-minute rainfal I = 0.24 inch Maximum 15-minute rainfal I = 0.45 inch Maximum 60-minute rainfal I = 0.47 inch MCINTYRE GULCH NO. 1 AT DENVER FEDERAL CENTER, AT LAKEWOOD T" ■ ~r L ~T L T T I \ T.4S. 1400 ^00 1600 iHOURS Total rainfal 1=0.13 Duration of rainfall = 10 minutes Maximum 5-minute rainfall =0.08 inch Maximum 15-minute rainfall = 0.13 inch Maximum 60-minute ramfa 11 = 0.13 inch ZINNIA WAY NEAR WARREN OCCUPATION TECHNICAL CENTER, AT LAKEWOOD Maximum 60-minute rainfall = 0.34 VILLA ITALIA STORM'DRAIN AT LAKEWOOD - O X 0 _ ! r.u HARVARD GULCH AJ HARVARD PARK AT DENVER --r 400 KEl^OD GULCH i < 1 L L ~T ~T 1400 1500 1600 ' YtOO^ TIME, IN HOURS Total rainfall =0.00 inch Duration of rainfall = 0.00 minute Maximum 5-minute rainfal I =0.00 inch Tura^Th'iunn"5-minuTe raTnTal! = (T.OO'men Maximum 60-minute rainfall = 0.00 inch 851 SOUTH ARBUTUS AT LAKEWOOD T.5 S. 1 - T ~T L 1310 WEST GLENNON DRI’/E AT LAKEWOOD < I L L R.67 W. SOUTH PLATTE RIVER TRIBUTARY AT DENVER .u m UOO 1500 1 60^t) A M!>7L )d*_ / TIME I^N HOLmS'F.R CO / Total rainfal I = 0.2p inch -—Duration of rainfall = 140 minutes Maxiimum 5-minute| rainfal I = 0.06 inch Ma xllmum 1 5- m inutfe rainfal I =0.1 4 inch Maximum 60-minute rainfa|^0.20 inch 06710000. T.3S. EXPLANATION NONCONTRIBUTING AREAS RAIN GAGE WATER-QUALITY STATION STREAMFLOW-MONITORING STATION AND NUMBER T 1500 TIME, INIhQIIRS 1(100 N HOURS 1700 Total rainfal I = 1.41—'ilches Duration of rainfal I = ll Maximum 5-minute rainfall = 0.37 inch Maximum 15-minute fdinfall = 0. Maximum 60-minute rainfall = l/41 inches. Gulcl, rOX3h Total ra ^ Duratior 1500 TIME, Total rainfal I = 0.68 nch Duration of rainfall = 140 minutes MaxImnirrS-minuTe i'ainfatl = 0.12 inoli ' Maximum 15-minute rainfall = 0.26 inch Maximum 60-minute iainfalI = 0.63 inch AT MCWILLIAMS 1-1 T 1500 1600 TIME, IN HOURS nfal I =0.48 inch of rainfall =75 minutes 1700 1400 Bear Creek Lake'll of ramfa i4im 5-minfcae rainfall = 0.06 inch Maximum 15;rminute rainfall = 0.14 inch f600 IN HOURS h^fall = 0.1 6 inch ■+r= 25 minutes Maximum ^-minute rainfal I = 0.16 inch ..) T L L .J — 39”45' i-H OS F < X ^ 2 - HARN'ARD GULCH AT BETHESDA HARVARD GULCH AT BRADLEY SCHOOL,AT DENVER I TAL.AT D 5 NVE R 1 1400 T" T 1 SM tT|ie Total rainfall p C Duration of rirH 1600 IN HOURS 6^ inch alr = 85 minutes aximum 1 5-minute rainfal I = 0.21 mumSO-minuta rainfal I = 0.64 11500 06 71157 5' HARVARD HARVARD GlkcH TRIBUTARY AT ENGLEWOOP 'e O- L 1500 I. 1600 T7°° TIME, >N HOURS ' • ■ Total rainfall = 0.0\ inch Duration of rainfal I A 5 minutes Maximum 5-minute rawfaM = 0.01 in Maximum 15-minute rainfall = 0.01 Maximum 60-minutexBinfalI = 0.01 bch^le^rmI I T GAGE NEAR LITTLETON SANDERsjoN GULCH TRIBU AT LAKEWOOD I I I-1- T" "T" T" L T L . o X o _ U ^ 710000 1 - 140TT' ~r L I L I I 16 N HOU'' 9 inch 1 = 85 minu Maximum 5-minu|teyrainfa 11 = 0.07 ' '■‘Tt^aximum 1 5-m u t rCite rainfal I = 0.16 inch Maxiitibim 6_0:;f^ rainfal I = 0.42 inch i: \ rainfall = 0.09 H(ich j - ■ ■ j 1400 1700 1700 inch 1500 1600 TIME, IN HOURS Total rainfall =0.68 inch Duration of rainfall =125 minutes Maximum 5-mmute rainfall =0.13 inch Maximum 15-minute rainfal I = 0.31 inch Maximum 60-minute rainfal I = 0.58 inch HARVARD GULCH TRIBUTARY AT ENGLEWOOD AUXILIARY RAIN GAGE L L 1400 1700 L 1^ 1400 1700 1400 1500 1600 TIME. IN HOURS Tctal rainfall = 0.1 inch Di ration of rainfall = 55 minutes Mtiximum 5-minute rainfal I = 0.02 inch Meiximum 15-minute rainfal I = 0.04 inch M | Ax i mum SO - m t nuto ro i nfa l I ~ 0.1 0 i nch -- IS 0 160(3 2.TIME, IN H(7URS 1700 T.6 S.' Total raiT)lf-5l I = 0.43 Duration fef rainfall^96 minutes Maximum p-minutefTainfall = 0.16 irveh Maximum '1 5-mInutk rainfal | = 0.40 i i\ch Maximum feO-minute rainfal I = 0.42 inch S (^M^N HO\(RS I Total fainfa(\=0.76X(Tch^ ^ I DuratioiViSLL^aihfal I =^ i Maximum S-rmoj^ rainfall = ,LJi3Ajmum 1B-m>inme rainfal 1 = 0 M^i^j^nj>'60-minu't^^ainfal I = 0 Chaifield Lake, 7 39°30' — 105'15’ R,70W. Base from U.S. Geological Survey Front Range Urban Corridor. 1972 /Plane Canvo/i Ne.s ef \ oit 4 BIG DRY CREEK TRIBUTARY AT EASTER STREET, NEAR LITTLETON r - O X -J _ _J f 1 “ . f/1 VJ X L \ X X L DRY CREEK] TRIBUTARY I AT MTTLETON Hi--1- TOO, 3 inch - O X n _ 1 U ' 1500 1600 TIME, IN HOURS Total rainfal I = 0.61 inch Duration of rainfall =80 minutes Maximum 5-minute rainfal I = 0.1 0 inch Maximum 15-minute ra infal I = 0.27 inch Maximum 60-minute rainfal I = 0.57 inch T.66W. 104°45' CHERRY KNOLLS STORM DRAIN AT DENVER X X 0 1400 U ail iX X 1400 15S 1700 1600 IME, IN HOURS Total rainfal iV 1 .03 inches Duration of ral^fall = 90 minutes jm 5-min\te rainfal I = 0,17 inch MaximuiTKiS-rjXwite rainfal I = 0.46 inch Maximum bTJininuXe rainfall = 0.99 inch BIG DRY CREEK TRIBUTARY AT .'LITTLETON AUXILIARY RAIN GAGY - ^ 2 < 1 I \ 1400 1700 1500 1600 TIME,. IN HOURS Total rainfal I = 1.02 inches Duration of rainfal I = 80 minutes Maximum 5-minute rainfal I = 0.22 inch Maximum 15-minute rainfal I = 0.38 inch Maximum 60-minute rainfall =0.98 inc L 1500 1600 1700 TIME. IN HOURS Total rainfal I = 0.69 inch Duration of rainfall = 1 50 minutes Maximum 5-minute rainfal I = 0.1 4 inch Maximum 15-minute rainfal I = 0.25 inch Maximum 60-minute rainfal I = 0.53 inch 1400 < 1500 1600 1700] TIME. IN HOURS Total feinfall=0.72 inch Duration of rainfal I = 90 minutes Maximum S-minute rainfall =0.12 inc Maximum 15-minute rainfal I = 0.31 Maximtwji 60-minute rainfal I = 0.67 V, R.69 W, 105°00' R.68W T.5S. T.6S. — 39-30' R.67 W. R.66 W. 104-45’ 5 MILES KILOMETERS MAP SHOWING LOCATION OF RAIN GAGES, WATER-QUALITY AND STREAMFLOW-MONITORING STATIONS, DRAINAGE BASINS AND NONCONTRIBUTING AREAS, AND RAINFALL DATA AT RAIN GAGES FOR STORM OF AUGUST 14, 1980, SOUTHERN DENVER METROPOLITAN AREA, COLORADO WATER-RESOURCES INVESTIGATIONS REPORT 83-4138 r^micx^y dbrary plate 2 R.67 W. DAMS CO NVHR CO ▼ 06710000j^ 39 ^ 45 ' EXPLANATION MONITORED TRIBUTARY BASINS NONCONTRIBUTING AREA WITHIN MONITORED TRIBUTARY BASINS UNMONITORED DRAINAGE AREA BETWEEN THE SOUTH PLATTE RIVER AT LITTLETON AND THE SOUTH PLATTE RIVER AT 19TH STREET UNMONITORED DRAINAGE AREA BETWEEN THE SOUTH PLATTE RIVER AT 19TH STREET AND THE SOUTH PLATTE RIVER AT 50TH AVENUE WATER-QUALITY STATION STREAMFLOW-MONITORING STATION AND NUMBER SUMMARY OF BASIC DATA LAKEWOOD GULCH Basin rainfall = 0,22 inch Basin storm runoff = 640,000 cubic feet Basin area = 10,400 acres WEIR GULCH Basin rainfall = 0.28 inch Basin storm runoff = 920,000 cubic feet Basin area= 4790 acres SANDERSON GULCH Basin rainfall = 0.32 inch Basin storm runoff = 1,300,000 cubic feet Basin area = 4720 acres BEAR CREEK Basin rainfall = 0.31 inch Basin storm runoff = 2,700,000 cubic feet Basin area = 15,400 acres CHERRY CREEK Basin rainfall = 0.29 inch Basin storm runoff = 4,200,000 cubic feet Basin area= 15,800 acres HARVARD GULCH Basin rainfall = 0.35 inch Basin storm runoff = 1,200,000 cubic feet Basin area = 2000 acres T.66W. 104°45' UNITED STATES DEPARTMENT OF THE INTERIOR GEOLOGICAL SURVEY Prepared in cooperation with the DENVER REGIONAL COUNCIL OF GOVERNMENTS WATER-RESOURCES INVESTIGATIONS REPORT 83-4138 rimioGy dbrary p^ate 2 EXPLANATION MONITORED TRIBUTARY BASINS NONCONTRIBUTING AREA WITHIN MONITORED TRIBUTARY BASINS UNMONITORED DRAINAGE AREA BETWEEN THE SOUTH PLATTE RIVER AT LITTLETON AND THE SOUTH PLATTE RIVER AT 19TH STREET UNMONITORED DRAINAGE AREA BETWEEN THE SOUTH PLATTE RIVER AT 19TH STREET AND THE SOUTH PLATTE RIVER AT 50TH AVENUE WATER-QUALITY STATION STREAMFLOW- MONITORING STATION AND NUMBER SUMMARY OF BASIC DATA LAKEWOOD GULCH Basin rainfall = 0.22 inch Basin storm runoff = 640,000 cubic feet Basin area = 10,400 acres WEIR GULCH Basin rainfall = 0.28 inch Basin storm runoff = 920,000 cubic feet Basin area = 4790 acres SANDERSON GULCH Basin rainfall = 0.32 inch Basin storm runoff = 1.300,000 cubic feet Basin area = 4720 acres BEAR CREEK Basin rainfall =0.31 inch Basin storm runoff = 2,700,000 cubic feet Basin area = 15,400 acres MAP SHOWING LOCATION AND AREA OF MONITORED TRIBUTARY BASINS, NONCONTRIBUTING AREAS WITHIN MONITORED TRIBUTARY BASINS, UNMONITORED DRAINAGE AREAS, AND BASIN RAINFALL AND RUNOFF FOR THE STORM OF AUGUST 14, 1980, SOUTHERN DENVER METROPOLITAN AREA, COLORADO 00 ao H QfS O a. u cc u H < a. 1/3 z o H < H c/3 U > Z c/3 u u Qi Zi o c/3 Cz^ ec I os u H < S: H or < or £D 8 -i O UJ O Va rn » rO 3^ Hi H Z u z OS a> U J= > *“ O 'i ^ in Tj- CTi ro Bear Creek Lake Bear Creek Lake ^eek ^eek Cherry Creek Lake Cherry Creek Lake Chaifield Lake/ Chatfield Lake/ 1415-1430 HOURS 1400-1415 HOURS Bear Creek Lake Bear Creek Lake Cherry Creek Lake Cherry Creek Lake Chaifield Lake/ Chaifield Lake/ 1445-1500 HOURS 1430-1445 HOURS Bear Creek Lake Bear Creek Lake Creek Cherry Creek Lake Cherry Creek Lake Chaifield l^ake/ GEOLOGY LIBRARY UNITED STATES DEPARTMENT OF THE INTERIOR GEOLOGICAL SURVEY Prepared in cooperation with the DENVER REGIONAL COUNtH PF GOVERNMENT WATER-RESOURCES INVESTIGATIONS REPORT 83-4138 PLATE 3 Base from U.S Geological Survey Front Range Urban Corridor, 1972 1500-1515 HOURS 1515-1530 HOURS 10 L 15 MILES 10 T 15 KILOMETERS O.lin ■ 0.112 0.02 -0.04 EXPLANAI ION RAINFALL, IN INt llHS j 0.04-0.0(1 0.0(1-0.OS 0.OS -0.10 PRECIPITATION MAPS BASED ON RADAR-SIMULATED RAINFALL DATA REPRESENTING SIX CONSECUTIVE 15-MINUTE INTERVALS FROM 1400-1530 HOURS ON AUGUST 14, 1980, SOUTHERN DENVER METROPOLITAN AREA, COLORADO 55/.V*?, ^ GEOLOGY LIBRARY WATER-RESOURCES INVESTIGATIONS REPORT 83-4138 PLATE 4 R.67 W. Quid LAKEWOOD GULC *Barnum Luke GULCH Harvard Sjulch HARVARD 'C-herrv Creek PUitle Canyon Reservoir UNITED STATES DEPARTMENT OF THE INTERIOR GEOLOGICAL SURVEY Prepared in cooperation with the DENVER REGIONAL COUNCIL OF GOVERNMENTS GEOLOGY LIBRARY WATER-RESOURCES INVESTIGATIONS REPORT 83-4138 PLATE 4 105°15’ R.70 W. R.69 W. 105'00' R.68W. R.67 W. EXPLANATION RAINFALL, IN INCHES NONCONTRIBUTING AREA ^ WITHIN MONITORED TRI¬ BUTARY BASINS 39”45' 0.10 - 0.15 0.16 - 0.20 0.21 - 0.25 ADAMS CO DENVER CO 0.26 - 0.30 J ^ 0.36 - 0.40 T.66 W 104"45 R.69 W. 105“00' R.68W R.67 W. 104M5 R.66 W. 5 MILES T.6S. 39°30' — — 39'30' 105n5' R.70W Base from U.S. Geological Survey Front Range Urban Corridor, 1972 5 KILOMETERS PRECIPITATION MAP BASED ON RADAR-SIMULATED RAINFALL DATA FOR 1330-1630 HOURS, AUGUST 14, 1980, SOUTHERN DENVER METROPOLITAN AREA, COLORADO it^s3-m3’5 GEOLOGY LIBRARY WATER-RESOURCES INVESTIGATIONS REPORT 83-4138 PLATE 4 R.67 W, EXPLANATION RAINFALL, IN INCHES 0.10 - 0.15 0.16 - 0.20 0.21 - 0.25 0.26 - 0.30 0.31 - 0.35 0.36 - 0.40 0.41 - 0.45 A UNIVERSITY OF ILLINOIS-URBANA 3 0112 098717066