Groundwater Flooding Solutions Through Collaborative Learning Framework

Since the 1970s, residents of Falls City, a small town in the foothills of Oregon’s Coast Range, have excavated a network of drainage ditches to divert floodwaters during heavy winter storms.  These diversions lack a cohesive hydrologic strategy.  Landowners often independently drain their land, sending water to downstream neighbors, creating considerable conflict in the small community.  OSU researchers have introduced a collaborative learning framework to help reduce conflict and simultaneously gather local expertise to work towards a solution.  Weather, stream and geologic records are combined with valuable local knowledge to provide a preliminary picture of flooding dynamics.  Observations suggest that groundwater drives the observed flooding.  A geotechnical survey is conducted to assess the surface and subsurface hydrology of the South Falls City Flooding Zone.  A monitoring well is installed to measure alluvium depth to bedrock and investigate subsurface processes in south Falls City.  Seasonal water table fluctuations and aquifer tests are used to characterize the hydraulic properties of the aquifer.  Results show that groundwater flooding plays an active role in the stormwater flooding.  Minor surface diversions will not likely eliminate flooding during high precipitation events.  LiDAR elevation data and HYDRUS modeling software are used to simulate several engineered dewatering measures to mitigate flooding.  These measures are combined with community sourced surface diversion to create a comprehensive flood mitigation plan for South Falls City.  The South Falls City Flooding Zone is yet another identified case of groundwater flooding and will worsen if global climate shifts increase storm intensities in the Pacific Northwest.  Similar community collaboration, however, could be useful for rural communities that need to adapt to harsh winter flooding.