Performance Evaluation of Ditch Check Practices During Earthwork Construction
As the list of impaired waters in Iowa continues to grow, stormwater management is becoming increasingly important in Iowa, especially in construction activities. The National Pollutant Discharge Elimination System Construction General Permit (NPDES Permit) requires developers to employ stormwater pollution prevention plans for any construction activities larger than one acre in disturbance. The stormwater pollution prevention plan is a comprehensive plan for the design, installation, and maintenance of erosion and sediment control (E&SC) practices used on site. Currently, the Iowa DOT has specifications, standard drawings, and guidance for the design of E&SC practices. Many of the practices included in these documents had not been formally evaluated for field performance. Furthermore, recent research performed by other state highway agencies has led to the development of new and improved erosion and sediment control practice. Opportunities existed to better understand the performance of standard Iowa DOT erosion and sediment control practices, improve the design and performance of practices, and to develop additional design manual guidance for the proper selection and design of practices. The project scope included perimeter control practices, detention basins, and various channel ditch checks.
This two-year research study, funded by the Iowa Department of Transportation, evaluated the performance of temporary erosion and sediment control practices, predominantly ditch check practices, on the Highway U.S. 30 Expansion project in Tama County, Iowa. Field evaluations were conducted for both current Iowa DOT approved ditch check practices and trial modifications of improved practices. Ditch check practices were evaluated over four months and included: 1) standard and modified wattle ditch protection installation with varying fill medias (i.e. excelsior, straw, woodchips, and switchgrass,), 2) standard and three (3) modified silt fence ditch check installations, and 3) standard rock check dam. Modifications to silt fence ditch check installations included wire reinforcement, dewatering weir, and angle of installation. Wattle ditch protection modifications implemented non-destructive teepee staking, special ditch protection underlay, and pins to enhance ground contact between the wattle and channel. Proposed rock check dam modifications planned to implement a geotextile underlay and overlay. To compare installations, data collection included LiDAR scans and upstream staking to assess erosion reduction and sedimentation capabilities of the practices. In addition, post deflection measurements and visual/ forensic studies were completed intermittently to evaluate the structural integrity and failure modes of the ditch checks. This poster will present the research findings and analysis on the performance of common ditch check practices used on DOT construction sites.