Grimes, Iowa

North Walnut Creek Grimes Watershed Study

  • Client City of Grimes
  • Type Stormwater
  • Services Assessment, Evaluation, Planning
  • Project Manager Steve P. Soupir, P.E., CFM


To provide sound stormwater management practices within the North Walnut Creek Watershed and meet growing development needs, the city needed an evaluation of the watershed to study past development as well as consider future stormwater management needs. This included review of existing land development, urban land management, rural land management, a hydrologic and hydraulic analysis, and an assessment of the stream corridors within the study area. In addition, flooding is often a concern in the North Walnut Creek Watershed. This study was used to evaluate areas of flooding concern to assist the city in planning for future development.


The goal of this study was to continue the process of proactively addressing stormwater quantity and quality within the study area.  This required developing new hydrologic models for past and existing conditions, alternatives for possible flood prevention improvements, water quality improvements, and watershed management. The study included the following primary elements:

  • Information gathering and base mapping
  • Evaluation of the watershed characteristics
  • Development of a hydrologic model of the watershed to evaluate estimated peak stormwater flows
  • Review and assessment of the watershed’s water resources and problem areas
  • Recommendations for stormwater management strategies



The study highlighted stormwater management opportunities within the study area. This included opportunities in rural and urban areas, as well as along stream channels. Recommendations were provided for rural areas for implementation of farming practices to reduce the impact from agricultural areas including buffer strips, cover crops, farm ponds, constructed wetlands, and no-till farming conservation practices. Stream channel opportunities included buffer strips and greenways along stream corridors as well as providing an example stream buffer protection and management ordinance to be implemented for new development areas. Recommendations for urban areas included sustainable improvements such as native turf, native landscaping, rainwater harvesting, rain gardens, soil quality restoration, bioretention, rain gardens, grass swales, infiltration trenches, porous pavement, extended detention facilities, and regional retention facilities to reduce downstream flooding.  Low Impact Development (LID) design methodology was evaluated to determine the net impact of these practices within the watershed.