Colorado - Grand County Stream Flow Mgmt Plan Phase III_Application II (3)

Home Browse Search

Scope of Work 3.4 Prepare Restoration Master Plan. The work effort for this task shall generally include the following: development of conceptual (35%) level of design; hydrologic, hydraulics and geomorphic analyses; and conceptual cost estimate. 3.4.1 Hydrology For the selected restoration sites use gage information, where available, to estimate peak flows for the 1.5-year, 2-year, 10-year and 100-year return interval peak flows. Where gage information is not available or not adequate, develop hydrology using HEC HMS an appropriate methodology for the given basin. Methodology may be dependant on the site's location and if any other existing information is available. Some calibration may be performed depending on availability of records. The goal of this analysis is to estimate the peak flow hydrology in order to perform hydraulic analyses. 3.4.2 Hydraulics and Geomorphic Assessment Utilizing cross sectional surveys develop a hydraulic model (HEC RAS) for restoration sites. Contractor shall perform a hydraulic and geomorphic assessment as outlined below. The goal of this analysis is to identify meandering, braided and transitional reaches of the river, assess trends in the study reach and estimate impacts of the proposed river restoration improvements on the river's geomorphology. )> Survey approximately lOO river cross sections and develop the HECRAS model. )> Using hydrologic conditions prepared in Task 3.4.1 develop a HECRAS for the existing conditions for the representative l.5-year, 2-year, lO-year and 100-year return interval peak flows. )> Evaluate at each project site the hydraulic conditions and calculate hydraulic parameters for the discharges noted above. )> Collect and analyze stream bed material gradations. For the purpose of this analysis six sites will be selected with one sample taken from each site for a total of six samples. )> Review hydraulic characteristics, bed material and other characteristics to compare with typical procedures to determine stream parameters. Review river reaches for trends in meandering, transitional or braided sections. )> Determine incipient motion sediment sizes for each reach for the range of flows extending up to the lOO-year peak based on average-reach parameters. The sizes moving should be compared with the bed material distributions to evaluate the percent of the bed mobilized at various flow levels and to identify any potential deposition zones that would be more prone to braiding. )> Review available thalweg and/or water surface profiles to identify if there is a change in gradient that might tend to result in sediment deposition or degradation. Review available Stream Management Plan TETRA TECH ~ Grand County, Colorado TETRA TECH 3