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<br /> Mr. Brian Genovese, P.E. AGI <br /> City of Eugene Public Works Engineering `E`""°`°"ES <br /> A CDM COMPANY <br /> May 17, 2000 <br /> Page 2 <br /> Task 2 -Explorations/Lab Testing/Report -AGI/CDM will provide a mini track or rubber-tired <br /> backhoe capable of excavating test pits to a depth of about 5 feet. The existing pipe was probably <br /> placed at grade in the original streambed. We would like to know soil characteristics at and 2 to 3 feet <br /> below the original streambed. We estimate that a 5-foot reach would be adequate to explore the new <br /> channel areas and that four test piss locations will adequately explore the area. We will collect <br /> representative bulk soil samples. An experienced geologist will log the test pits and return the <br /> samples to our laboratory. Laboratory testing will be limited to natural moisture contents on all <br /> samples and a maximum of three grain size analyses on representative samples. A brief letter report <br /> will be prepared that describes the site soil conditions and presents logs of the test pits together with <br /> location plans. <br /> Task 3 -Erosion Protection and Waterway Enhancement Studies -Inter-Fluve, Inc. will work directly <br /> with the City to develop a concept stream enhancement design that is compatible with the <br /> neighborhood, environmentally sensitive, and addresses City criteria. <br /> A. Review Existing Information. IF will review the following existing information: (a) existing <br /> data, model development assumptions and results of the existing XP-SWMM model; (b) letter <br /> report dated January 4, 2000 prepared by URS Corporation describing the drainage system <br /> and existing problems; (c) letter report dated March 10, 2000 prepared by URS Corporation <br /> describing a preliminary conceptual design; and (d) City's plan for habitat and water quality <br /> features. <br /> B. Estimate Geomorphic Design Parameters. Geomorphic stability is attained when sediment <br /> transport capacity is equal to sediment supply (particle size and/or volume), such that erosion <br /> and deposition are balanced, and approximate channel dimensions and form are maintained. <br /> Using predictive equations, estimate and apply acceptable ranges of geomorphic design <br /> parameters (including channel slope, cross section geometry, plan form, and substrate size) to <br /> provide geomorphic stability and natural diversity. <br /> C. Perform Hydraulic Calculations. Consider the design flows, velocities, and channel gradient <br /> within the open waterway reach under consideration. Develop hydraulic calculations to <br /> refine the proposed channel and over bank geometry and to estimate depth, velocity, and <br /> shear stress for the design discharge. Channel shear estimates will be used for bed and bank <br /> material sizing and selection of appropriate bank. <br /> To complete this task, IF assumes the City will provide a topographic map of the project area <br /> (between Frederick Court and West 37`" Avenue) with a contour interval of no more than 2 <br /> feet and as--built drawings of the existing storm drains (showing existing manhole and pipe <br /> invert elevations. )F assumes the topographic map and as-built drawings will be provided in <br /> an AutoCAD 14 compatible format. <br /> D. Estimate Incipient Motion Particle Size. In urban settings, the duration and magnitude of runoff <br /> in response to rainfall has increased dramatically from historic pre-development conditions. <br /> As a result, urban and disturbed streams are capable of transporting larger volumes of <br /> sediment and larger rock sizes. For this reason, many urban creeks have severely eroded <br /> streambeds and banks. One approach to creating a stable channel is to design the streambed <br /> material to be stable (i.e., to stay put) during the design discharge. Incipient motion is the <br /> Eupn. Reh w~r.+rw~trnnArwrco F.a.id caA[wr Ero~fanea <br /> <br />