2016-04-25-minutes-public-works-study-session

Home Browse Search

Kittitas County Via Kachess Road Lodge Creek Culvert Replacement Hydraulic Design Scope of Work Kittitas County Department of Public Works plans to replace an existing damaged culvert that carries Lodge Creek under Via Kachess Road. The crossing was damaged during recent high water, is undersized, and is a barrier to fish passage. The County has asked Watershed Science and Engineering (WSE) to provide hydraulic design assistance for the replacement design. The following scope of work is divided into two parts. Part 1 describes the tasks needed to determine the required culvert size, while Part 2 presents the follow-on tasks required to complete the hydraulic design should the County choose to have WSE provide the additional support. Part 1 — Culvert Size Determination I. Data Collection WSE will collect existing data and information needed to complete hydraulic design_ Items may include, but are not limited to, existing watershed and stream topographic data, LIDAR, current and historical aerial photographs, existing crossing plans (if they exist), and maintenance records. 2. Site Reconnaissance and Channel Survey WSE staff will travel to the project site to: 1. Examine the geomorphic and hydraulic characteristics of Lodge Creek both upstream and downstream from the crossing. 2. Survey the longitudinal profile of the stream channel for a distance of approximately 500 feet upstream and downstream from the road. This will include a survey of the culvert invert and to the extent possible, scour plunge pool. 3. Surrey representative cross sections of the stream channel, floodplain and road fill. Approximately four cross sections will be surveyed downstream and three upstream. 4. Hand measure the natural top width of the stream channel at 10 to 15 locations to supplement the surveyed channel cross section data from the task above. The purpose is to provide an estimate of the natural geomorphic regime channel top width, a measurement needed to calculate the required width of the new culvert. Note — The survey will be completed by the WSE field crew. It is solely intended to support the channel width (Part 1 task) and profile stability investigation (Part 2 task). WSE will set a temporary bench mark (TBM) at the project site which will be assigned an arbitrary datum elevation of 100 feet. The actual elevation of the TBM will be surveyed by the project surveyor, if one is retained to complete a road survey to support civil design. 3. Field Data Analysis Upon return to the office, WSE will process the field data then use it to create tables and figures, to present the channel width measurements and recommendations.