Hydrologic modeling of overland flow within Little Beaver Creek, Iowa

• Main Author: Morgan, Steven Russell
• Format: Text
• Language: English
• Published: Iowa State University Digital Repository 2001
• Subjects: Landscape architecture; Beaver Creek
• Online Access: https://lib.dr.iastate.edu/rtd/21453; https://lib.dr.iastate.edu/cgi/viewcontent.cgi?article=22452&context=rtd

This research models the effects of land management practices and policies on overland flow within the Little Beaver Creek watershed, Iowa. The research was conducted because of the concerns of local residents and members of the Iowa Army National Guard. Their concerns include flooding and erosion due to increasing urbanization within the Little Beaver Creek watershed. Modeling addressed the effects of increased urbanization on water quantity within the watershed. The effects of urbanization on water quantity were modeled using two hydrologic models, TR-55 and TR-20. The models were developed by the USDA Natural Resources Conservation Service to estimate overland flow and peak discharge rates of selected rainfall frequencies. The TR-20 model was used to estimate the overland flow of four land cover condition scenarios: historic land cover maps and data, current land cover, and two residential suitability models. The residential suitability models were created utilizing residential development suitability criteria developed by the City of Johnston and by the Dallas County Conservation Board. Field research was completed to gather pertinent stream channel data: cross-section elevations, cross-section area, channel conditions, photographs, and flow velocity. The results of the overland flow and peak discharge modeling suggest the predominant alterations of the Little Beaver Creek stream network are currently taking place due to extensive agricultural use within the watershed. The modeling results were used to compare the hydraulic capacity of each stream channel to the TR-20 peak discharge estimates based on the current land cover conditions. The hydraulic capacities of specific stream channels were insufficient to carry the estimated peak flows during rainfall events greater than a 5-year storm for three stream segments. The current land cover condition scenario results show a dramatic increase in estimated overland flow and peak discharge (3,075 cfs) for a 25 year 24-hour rain event compared to the historic (2,107 cfs) and residential suitability model scenarios (2,309 cfs, 2,337 cfs). The results of the TR-20 analysis suggest that residential development may mitigate increased overland flow and higher peak discharges. The results of the residential suitability modeling and TR-20 modeling provide information for altering and developing management practices and policies (for example, agricultural riparian buffers and rezoning) within Little Beaver Creek watershed.