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Spring Valley Subdivision Storm Water Rehabilitation Project

Spring Valley Subdivision was constructed in the early 1980's in an area that was previously agriculatural land.  The original design utilized an existing stream located in a wooded area to store storm water by installing a large dam structure downstream of an intersection of two drainage channels.  The subdivision's storm sewer systems empties into each channel upstream from the detention area.  Over the years, the flow from the storm sewer systems have eroded the channel bottoms approximately five feet below the storm sewer outlet aprons at each location.  The erosion has created unstable banks, falling timber, loss of private yards, and eight feet of siltation within the storm water detention area.  The frequent overtopping of the dam structure has created erosion around the structure itself on the downstream side.

The City of Ames hired CGA in 2011 to engineer a design that would be sustainable and low maintenance for this area with minimal tree distrubance.  CGA's field crews collected topographic data with identification of eroded areas.  The project engineer hosted an initial Public Input Meeting to allow residents to give input on the project and it's timeline.  The watershed was broken up to model flows to each channel as well as the overall detention basin.  Each channel was analyzed to determine the most sustainable slope, channel section, channel lining method, and side slope protection.  Multiple solutions were examined for each to determine the most cost effective and low maintenance solution.  The storm water detention area was examined for flows ranging from a 2-year flow to a 100-year flow to determine ponding elevations.  A Project Drainage Report was prepared for the City to justify the design solution chosen and was presented to the neighborhood at a Public Meeting prior to finalizing plans.

The final design utilizes the creation of uniform channel sections with rip-rap lined bottoms, storm sewer extensions, vegetated geogrid placement to stabilize eroded slopes, live stake planting above the 5-year flows to stabilize existing slopes and on the downstream side of the existing dam, a new low flow perforated riser structure, permanent turf reinforcement mat (TRM) from the rock lined bottom to the 100-year detention basin elevation, and a riparian seed mix below the (TRM) in the detention basin.

Spring Valley Subdivision Storm Water Rehabilitation Project

Spring Valley Subdivision Storm Water Rehabilitation Project

 

 

 

Project Summary

  • Total Cost = $110,000 (est)
  • Completed: 2013