Holistic Watershed Management
The Walnut Creek Watershed Management Authority (WMA) was formed to ensure that flooding and water quality concerns were being handled on a holistic level. This is opposite of how these concerns have been handled in the past, which has been site-specific solutions with little consideration given to finding the root cause of the issue.
As a part of the Watershed Management Team, Snyder & Associates provided services to ensure the floodplain in and around Walnut Creek was as accurate as possible. This allows communities and residents to more accurately assess risk profiles along the creek corridor. We were also involved in the ever-important stakeholder engagement process. Stakeholders across a wide cross-section of groups were asked to provide input and guidance regarding what goals should and can be for the Watershed Management Authority. High engagement from stakeholders throughout the watershed is the backbone for success.
Snyder & Associates was contracted to update the hydrologic and hydraulic modeling for the North Walnut Creek watershed. The modeling performed updated hydrology for the entire watershed (14 sq. mi.) using HEC-GeoHMS and updated 10.5 miles of the hydraulic models using detailed methods in HEC-GeoRAS including floodway calculations. The hydraulic modeling included North Walnut Creek and two of its tributaries. Flood inundation mapping was performed for all three studied reaches. Final data was compiled in a report for LOMR submittal to FEMA.
The existing hydrologic model for North Walnut Creek had not been updated for quite some time, and there had been ample amounts of development in the watershed since the last study. Accurately assessing current development within the watershed was paramount while calibrating the hydrologic model.
The existing hydraulic model was also in need of an update. Not only to take advantage of the updated hydrologic model but to take advantage of current field conditions and new Iowa Statewide LiDAR data. LiDAR was also used as the base for the Digital Elevation Model to produce accurate floodplain mapping.
The final products provide the City a tool for more effective community planning. Most importantly, the data allows current and future residents to be more accurately informed regarding their flood risk. The goal is to eliminate future risks and to mitigate current risks, as applicable.