Evaluation of Changes in Water Quality and Urban Runoff in the Buck Gully Watershed, California, Through the Use of Weather-Based Irrigation Control

The Buck Gully watershed is located in the Newport Coast area of California. Buck Gully is located in a coastal canyon which drains into an area designated as a State Water Quality Protection Area (formerly Area of Special Biological Significance). The adjacent coastal land is designated as a Critical Coastal Area. The upper portion of the watershed is in the Newport Coast area, and water service is provided by Irvine Ranch Water District (IRWD). The primary source of the non-point source pollution that enters the Buck Gully area is runoff from surrounding commercial and large residential developments. Previous studies by the Municipal Water District of Orange County and Irvine Ranch Water District (Residential Runoff Reduction Study 2003) have successfully demonstrated that the use of weather-based irrigation controllers reduced water consumption and runoff. The Buck Gully Project was designed to take the next step. That is, by utilizing weather-based irrigation scheduling and providing only the amount of irrigation necessary (not over-watering) it is possible to reduce runoff, and correspondingly, reduce the quantity of nutrients running off, to the streets, to the storm drains, and ultimately to the ocean and beaches. IRWD staff surveyed the Buck Gully Watershed to determine the appropriate locations for monitoring stations. The upper two monitoring locations were site 3001 (Control Site) and 3011 (Retrofit Site). Pre-controller installation flow data was gathered from May through October in 2003 and pre-installation water quality data was collected in 2004. No controllers were installed within the Control area. In the Study Site, 55 weather based irrigation controllers were installed between December 2005 and April 2006. IRWD collected post-installation flow data and weekly water quality data from May to October 2006. Kennedy/Jenks Consulting was retained by the Municipal Water District of Orange County (MWDOC) to conduct the statistical evaluation of the runoff and water quality data. Kennedy/Jenks analysis showed a statistically significant reduction in dry-season runoff resulting from the installation of the weather-based irrigation controllers. This paper describes the runoff reduction project and water quality evaluation.