1 LOCATING DITCH RELIEF CULVERTS TO REDUCE SEDIMENT DELIVERY TO STREAMS- AN INTERACTIVE DESIGN TOOL

A model has been developed which allows a designer to optimize the location of ditch relief culverts to minimize sediment deliveries to streams. The model provides immediate visual feedback allowing the designer to rapidly evaluate and optimize various ditch relief culvert locations. The model’s sediment delivery and routing algorithms are based on existing methodologies. Current as well as planned road systems can be evaluated and the potential for improvements documented in a quantifiable and repeatable way. The model was tested on a portion of the Tahoma State Forest, situated south of Mt. Rainier. Two existing road systems with 28 and 39 stream crossings and 82 and 86 ditch relief culverts respectively were analyzed. Interactively relocating 20 and 35 ditch relief culverts resulted in a 76 % reduction in sediments delivered to each stream system. The last culvert was usually placed 100 to 200 feet from a stream