SPDSS_Task34-3_Phase 3_StreambedConductanceTesting

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were not sufficient to supplement the study because they did not provide enough detail to characterize channel geometry or adequately define the streambed grain-size distribution. Additionally, the CWCB Flood Protection Program's detailed floodplauz cross sections along the South Platte River were evaluated to determine whether t11e data could be used in place of perforn~lg channel cross section surveys in the field program. T11e Flood Protection Programs cross sections did not provide enough detail to characterize channel geometry;llowever, these data will be used >11 t11e groundwater modeling (Task 48) as supplemental data to characterize floodplain shape and extent. Cross sections provided by the Urban Drainage and Flood Control District (UDFCD) and from the USGS and the DWR stream gaging programs were obtained and determined adequate for Task 34 and are incorporated in this TM, as described in Section 2.1. 2.1 Channel Cross Section Profiling Streambed geometry was defined at each field test site by obtaining stream channel cross section information at all 301ocations. At nine locations, the stream channel cross section data were already available from cooperating entities. Therefore, a cross section survey was not conducted at these locations duriizg field activities. At six of the seven stream gaging locations (SC-06, SG14, SG17, SC-21, SG23 and SG30), streambed geometry data were provided by the entity operating the gage (USGS or DWR). Location SG07 is near the Fort Lupton Wastewater Treatment Plant on the Sout11 Platte River, and the cooperator supplied CDM wit11 cross section information. T11e UDFCD provided cross section data in the vicinity of locations SG02 and SG03, both located along the South Platte River. Twenty-one sites were surveyed for cross section data by CDM. These stream channel cross sections were surveyed to a temporary benchmark using a manual survey level. To define t11e channel geometry, a survey reading was taken at eac11 change in slope along t11e streambed or every 10 ft when no significant change across the streambed was observed. Streambed cross section data provided by cooperating entities were for locations that were in the general vicinity of the coring and testing locations but did not match them exactly. Therefore, coring and testilzg locations are not presented on cross sections provided by cooperating entities. Additionally, most cooperating entities measured only the submerged part (wetted perimeter) of the stream, rather than the floodplain transects. These non-SPDSS cross sections are representative of stream stage and channel conditions existing at the time those sections were prepared. Stream chaiu~el cross sections provided by the DWR were selected from periods of relatively High flow conditions to provide a wider transect, and thus greater resolution to streambed geometry for the cross sections was provided. 2.2 Streambed Sediment Sampling At each site, a prelinunary corehole was sampled to evaluate initial site conditions and depth of streambed sediments. The core was visually evaluated for the presence of different sediment types that may indicate t11e contact between streambed sediment and t11e underlying alluvium, such as changes in color, grain-size, texture, and organic matter content. Field conditions dictated that not all sites could be sampled Fnlal T~zsl: 3~TM 06-28-07.doc