UC Cooperative Extension | Agricultural Experiment Station

Drainage waters discharged from irrigated fields in California and other states are under ever-closer scrutiny. The quality of drainage waters discharged into waterways in California is regulated under California Water Code and Federal Clean Water Act. Growers that discharge drainage waters that could affect the quality of water bodies in the state are required to comply with water quality regulations. Compliance with water quality regulations could be achieved by filing a Report of Waste Discharge (RWD) that complies with state-prescribed Waste Discharge Requirements (WDRs). WDRs could be used as a permit, limiting the levels of pollutants that may be discharged in waterways to protect the beneficial uses of water bodies in the state. Complying with the Irrigated Lands Conditional Waiver Program or the Total Maximum Daily Load (TMDL) limits may provide alternates to WDRs for growers in the state. Sediment, nutrients and pesticides in drainage waters have been identified as the leading cause of water quality impairments in rivers and other water bodies in California. For example, sedimentation/siltation TMDLs for agricultural drains and two major rivers in Imperial Valley have been implemented to address water quality problems in the Colorado River Basin of Southern California. Accurate and reliable estimates of the load of sediment, nutrients and pesticides in drainage water are needed to assess the quality of drainage water or to comply with WDRs.

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