Sloughs are generally wetlands, parts of old rivers where water once flowed, or quiet backwaters of bays where freshwater from creeks meets tidal ocean flows. Within the District, sloughs are natural ravines where water has historically flowed from storms or emergent groundwater but are not part of the canal system. Although not part of the canal system, the District will put water in the sloughs when a landowner adjacent to the slough orders it, or as drainage at the end of a canal. Irrigation water conveyed in sloughs plays an important role in maintaining the valley’s riparian habitat, and helps to support a diverse array of plant, animal, and insect species. Sloughs not only play a part in supporting riparian species, but also in improving water quality by filtering sediment out of water and slowing the flow of water down so it can increase groundwater recharge.
Although sloughs are an important part of the ecosystem, they do represent a challenge because accumulation of natural debris can increase localized flooding during storms. There is no county-wide management of sloughs, but the District is responsible for maintaining some sloughs via an agreement with Yolo County (see map). The District’s primary objective in regard to slough maintenance is to maintain the flow of water by removing obstructions such as weeds, brush, and downed trees that may cause flooding if not removed. Typically, no herbicides are used except when necessary to maintain water flow.