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Northridge Drainage Study

The flood event of 2010 not only affected the large creeks and rivers in the City of Ames, it also drew attention to localized flooding in some of the communities neighborhoods.  In 2007, the City of Ames partnered with Iowa State University to develop a local Hazard Mitigation Plan that enables the city to receive Federal Emergency Management Agency (FEMA) funds after natural disaster declarations.  In 2011, the City of Ames hired CGA to look at multiple areas all over the City of Ames and help them determine which areas could be mitigated with a justifiable benefit-cost ratio.  CGA assisted the city with public outreach and coordination with the Iowa Homeland Security and Emergency Management staff for ten potential projects.  The Northridge Subdivision was one of the areas hardest hit by the 2010 floods and is currently in the process of the FEMA HMGP Grant application.

CGA began the process with personal phone calls and site visits to the homes that had reported damage during 2010.  CGA discussed how water entered each of the nine homes and determined that flooding occurred due to inadequate overland flow paths.  An initial public meeting was held with the immediate impact area (approximately 35 homes) in August 2011 to discuss the flood history in the area.  Flood documentation was collected from the nine homes affected in 2010 as well as past flood events from half of the homes in 2008 and 2004.  One home was able to document yearly flooding since 1998.  CGA gathered 24-hour rainfall data from 1998-2001 and hourly data from 2001-present from the Ames Municipal Airport to correlate the documentation with specific rain events.

The entire watershed was broken into 12 drainage areas to create 26 hydrographs that included three existing stormwater storage basins, two low point intersections, and an existing pond located in the City's Moore Park.  All 12 areas were analyzed using the SCS Runoff Method and each basin, low point, and pond was modeled to determine peak elevations during 2-year to 100-year storm events.  The model was then modified by deepening existing ponds, lowering over flow paths, and the creation of a new pond to modify the high water elevation to keep it below existing floor and window well elevations in order to develop a mitigation solution.  The Hydrology analyzed for the project was documented in a Preliminary Engineering Report (PER) along with the proposed solution and detailed associated costs also completed by CGA.  The PER is an essential supporting document and is being used to compete the application for this project.

Northridge Drainage Study

Northridge Drainage Study

 

 

 

Project Summary

  • Total Cost = Estimate at $330,000
  • PER and Application:  Completed in 2012
  • Construction:  Dependent upon Funding