Selected hydrologic data for the south Platte River through Denver, Colorado

Abstract

The U.S. Geological Survey, in cooperation with the cities of Littleton and Englewood, Colorado, studied the effects of the discharge of treated effluent from the Bi-City Waste Water Treatment Plant on low-flow conditions of the South Platte River. An 18-mile reach of the South Platte River beginning below Chatfield Reservoir and continuing through the Denver metropolitan area was studied. Chatfield Reservoir was used to regulate the flow of the South Platte River on four occasions between October 1982 and January 1984. Each flow-regulation period was used to achieve a stable low-flow condition. Data collection during low flow allowed for the study of waste assimilation during both warmand cold-water conditions. Water-quality, streamflow, channel geometry, traveltime, mixing-zone, reaeration, and benthic-oxygen demand data were collected at selected instream, tributary, and effluent sites. This report presents data collected during four periods of low flow along the South Platte River. INTRODUCTION The U.S. Geological Survey, in cooperation with the cities of Littleton and Englewood, entered into an agreement to study the effects of the discharge of treated effluent from the Bi-City Waste Water Treatment Plant (WWTP) on the quality of water in the South Platte River during low-flow conditions. This report presents data collected during four periods of low flow on the South Platte River. SCOPE The reach of the South Platte River studied ranges from approximately 1.0 mile below Chatfield Reservoir downstream for about 18 miles to the streamflow-gaging station 06714130, South Platte River at 50th Avenue, at Denver. The WWTP effluent enters the study reach approximately 8 miles downstream from the first sampling point. DESCRIPTION OF HYDROLOGIC DATA Data were collected during four periods of low flow on the South Platte River. During each of these periods, flow from Chatfield Reservoir was regulated at a constant discharge for 5 days. Flow regulation was required to achieve a stable condition in the study reach. Flow-regulation periods or data-collection periods were scheduled to study waste assimilation during both coldand warm-water conditions. The data-collection effort during March 1983 was aborted due to unstable flow created by a rain-and-snow storm. During the flow-regulation periods, water-quality and streamflow data were collected at the 18 instream sites shown in figure 1. Tributary, industrial effluent, and municipal effluent sites at which water-quality and streamflow data were collected are shown in figure 2. A listing of instream and tributary sites and their corresponding study reference code names is given in table 1. Study reference codes for instream sites are prefixed with an 'SP'; study reference codes for tributary sites are prefixed with a 'TR'. Numbers following the 'SP' for instream sites were incremented by 100, starting with the upstream site of SP-100. Site SP-1100A was added to the study after the initial site reference codes were established. The number following the 'TR' prefix represents the relative position the tributary site has with respect to instream sites and other tributary sites. For example, TR-310 is located downstream from SP-300 and upstream from TR-320. Water-quality samples at instream sites were collected from the surface to the bottom at several verticals across the stream using a composite sampler. Grab samples were collected at other sites. Phosphorus and suspendedsediment samples were collected at only seven instream sites. After the flow-regulation period of October 1982, flow from site TR-1120 (Lakewood WWTP effluent) was rerouted and did not enter the South Platte River within the study reach. Discharge measurements were made at water-quality sampling sites. At most sites, staff gages were installed for the flow-regulation period. Staff readings from one flow-regulation period cannot be related to staff readings from another period, because shifting of the staffs occurred between datacollection periods; therefore, staff readings are only usable during an individual data-collection period. Discharge values of 0.0 ft 3/s represent no flow. Channel-geometry measurements were made at 54 sites on the South Platte River. Locations of these sites are shown in figure 3; the sites are listed in table 2. Channel-geometry measurements consist of setting up a cross section and measuring the width of the river. Depths of the water are then measured at approximately 20 equally spaced verticals in the cross section. The type of bottom material also was noted for each cross section and is listed in table 3. Traveltime and reaeration measurements were made during three of the flow-regulation periods. Traveltime and reaeration measurement sites are shown in figure 4.