The Cache Creek Area Plan ("CCAP") was adopted by the Yolo County Board of Supervisors in 1996. The CCAP consists of the Off-Channel Mining Plan ("OCMP") and the Cache Creek Resources Management Plan ("CCRMP"). The goals of the CCAP are protection of groundwater, preservation of agriculture, restoration of Cache Creek, and regulation of commercial mining.

The CCRMP (adopted August 20, 1996, amended August 15, 2002, and December 17, 2019) is an adaptive watershed restoration and management plan. It eliminated in-channel commercial mining and established an improvement program for implementing ongoing projects related to channel stability and restoration of habitat within and along Lower Cache Creek. The CCRMP provides a policy framework for the restoration of 14.5 miles of the creek and includes specific implementation standards. The Cache Creek Improvement Program ("CCIP") is the implementation plan for the CCRMP and identifies specific categories of projects that include bank stabilization, channel maintenance, revegetation, and habitat restoration.

The CCIP is overseen by the Cache Creek Technical Advisory Committee ("Cache Creek TAC"), which is a three-person interdisciplinary group composed of a hydraulic engineer, a fluvial geomorphologist, and a riparian biologist. The Cache Creek TAC was established to provide scientific and technical review and oversight for all projects conducted under the CCIP, as well as collect and evaluate scientific data on hydrologic, hydraulic, sediment transport, and biological conditions within the CCRMP area. The Cache Creek TAC is currently staffed (via contracts held by the County) by the following subject-matter experts:

Section 2.2 of the CCIP requires that the Cache Creek TAC produce an annual report each year for the Yolo County Board of Supervisors. The report is intended to: 1) document the previous year's monitoring results, field observations, and completed in-channel restoration or stabilization projects; 2) provide analysis of data and trends; and 3) identify recommendations and projects to be implemented the following year(s). This report represents a critical component of the adaptive management of Lower Cache Creek.

The annual report subject to this staff report is for the 2024 Water Year, which covers the period of October 1, 2023, through September 30, 2024. The "Board of Supervisors Draft" of the report has been included as Attachment A.

SUMMARY OF 2024 WATER YEAR FINDINGS

Findings related to Hydrology and Water Quality

The 2024 Water Year was average for the State of California and Sacramento Valley. For Cache Creek, which is not affected by snow as is the greater Sacramento Valley, the water year was almost identical to 2023, which was considered “above normal” to “wet.”  Similar patterns of storm flows in January through April occurred, and almost identical summer irrigation releases down the creek occurred. The largest flow event of the water year occurred February 4-5, 2024, when flows of approximately 14,500 cubic feet per second (“cfs”) at Rumsey and 13,800 cfs at Yolo were observed. These flows represented approximately a 2-year return interval peak. Two additional events in late January and late February occurred which represented approximately average annual peak flow events (6,000 – 9,000 cfs).  Much like occurred in 2023, 2024 was characterized by a series of moderate and ecologically beneficial flows that did not produce significant damaging erosion.

Findings related to Geomorphology

As mentioned previously, Water Year 2024 was very similar to Water Year 2023 in the Cache Creek basin. There were slightly higher peak flow magnitudes in Water Year 2024, but the channel response was nearly identical to Water Year 2023. The peak flow at the Yolo USGS streamflow gage that occurred in early February 2024 was well below the threshold of 20,000 cfs required for significant sediment transport and channel change in Cache Creek. Therefore, while delivery and transport of sediment to, and through, the CCRMP area in Water Year 2024 was the fifth highest over the last 20 years, channel change due to erosion, scour, and deposition was localized and mostly relatively minor. The geomorphic conditions changed a bit more than in Water Year 2023, likely because 2023 peak flows loosened sediments and removed vegetation, and because the peak flow magnitude was slightly higher in 2024.

Because of the relatively moderate channel change in Water Year 2024, the recommendations developed by the Cache Creek TAC did not change substantially from recommendations made since 2023. Similar to 2023, the recommendation to monitor conditions at Huff’s Corner at the downstream end of the CCRMP area should be updated to assess conditions addressed by the repair work completed at that site. Channel conditions are expected to change at newly constructed sites in response to the magnitude of high flows observed in 2023 and 2024, so Huff’s Corner should be closely monitored in Water Year 2025, especially if wet conditions continue. In addition, because Water Year 2024 did result in significant sediment transport, the CCTAC Fluvial Geomorphologist recommends another comprehensive review of current recommendations be completed in Water Year 2025 after the high flow season and before the 2025 Creek Walk. The purpose of this review is to focus Creek Walk observations on expected areas of significant change and needs for revised recommendations.

Findings related to Biological Resources

The distribution, extent, and condition of native vegetation along Lower Cache Creek in 2024 was generally similar to conditions observed in 2023, with four notable exceptions: (1) increases in in-channel vegetation in areas where vegetation was observed to have been reduced in 2023 due to scour from 2022–2023 winter flows; (2) no significant new observations of drought-stressed native woody vegetation, as well as some recovery in areas observed in 2023 to have been significantly impacted by drought; (3) some minor loss of mature native woody vegetation due to scour and bank erosion resulting from winter 2023–2024 flows, and (4) increased impacts to native vegetation resulting from increased OHV activity. In general, significantly more OHV activity was observed during the 2024 Creek Walk compared to 2022 and 2023, especially in the Hoppin Reach.

Non-native and invasive plant species remain widespread along Lower Cache Creek, and continue to be one of greatest constraints to further recovery of native habitat. As in recent years, arundo, tamarisk, Ravenna grass, and other non-native species were frequently observed, and tamarisk especially appears to be spreading in some locations. As in 2022 and 2023, evidence of continued treatment of arundo and tamarisk was observed, which is a positive development.  Many additional non-native and invasive species (e.g., Himalayan blackberry, perennial pepperweed, and tree tobacco) remain common along Lower Cache Creek and should be prioritized for treatment and monitoring when and where feasible. After treatment of non-native and invasive species, native woody and herbaceous species should be planted whenever possible to enhance habitat and reduce the potential for re-invasion.
 
Many common and special-status species of wildlife, invertebrates, and fish were again observed by the Cache Creek TAC, Cache Creek Conservancy staff, and other Creek Walk participants during the 2024 Creek Walk. Swainson’s hawks (State threatened) were observed in six of the seven reaches, and as in 2022 and 2023 an occupied nest was observed in the Dunnigan Hills Reach.  Bald eagles (State fully protected) were observed at the Capay Dam and in and Hungry Hollow Reach, and a flock of American white pelicans (State species of special concern) was observed in the Hoppin Reach. At least five active colonies of bank swallows (State threatened) were observed in the Hoppin Reach, which represented the greatest number of colonies and holes observed on Lower Cache Creek for at least the last 10 years.  Numerous other potential bank swallow colony sites were also evaluated starting in the Hungry Hollow Reach and downstream to the Hoppin Reach. A total of 55 unique bird species were observed in 2024 including acorn woodpecker, Anna’s hummingbird, ash-throated flycatcher, blue grosbeak, Bullock’s oriole, cliff swallows, great horned owl, green heron, lesser nighthawk, marsh wren, red-tailed hawk, song sparrow, and wood duck. Western pond turtles (State species of special concern) were observed in deeper pools in the Capay and Guesisosi reaches.  Beaver dams were frequently observed during the 2024 Creek Walk, including a large beaver dam complex in the Dunnigan Hills Reach. Other wildlife species observed included, black-tailed jackrabbit, California ground squirrel, Columbian black-tailed deer coyote, desert cottontail, garter snake, river otter, wild pig and fishes including bluegill, common carp, green sunfish, and largemouth bass.
 
Priority opportunities for active habitat enhancement and restoration along Lower Cache Creek are essentially unchanged since 2019, with the focus on areas where enhancement and/or restoration are realistically feasible, where plantings will be at lower risk of impacts from high flows, and where native vegetation can be sustained with limited management through reliance on natural river processes. Such areas include flat upland areas on the north bank from river mile (RM) 26.8–27.8, the PG&E “Palisades” site (RM 26.8), Capay Open Space Park (RM 26.3), the Hayes “Bow-Tie” property (RM 20.0), the Millsap property (RM 18.5), Wild Wings Open Space Park (RM 17.0), the Correll and Rodgers properties (RM 13.7), the Capay Organic creek frontage (RM 27.9) identified in 2019, and former mining pits in the Dunnigan and Hoppin reaches (e.g., on the north bank from RM 15.0–15.4). On lower banks and within the main stream channel, where high flows can potentially scour and remove planted native vegetation, passive restoration of native woody vegetation through invasive species removal, streamflow enhancement, and strategic channel maintenance projects is likely the most efficient and effective means of accelerating native vegetation recovery.

SUMMARY OF 2024 WATER YEAR RECOMMENDATIONS

Recommendations related to Hydrology and Water Quality

The Cache Creek TAC Hydraulic Engineer recommends the following:

As in previous years, recommendations from the Cache Creek TAC Fluvial Geomorphologist for Water Year 2024 are in three general categories: monitoring, evaluation, and implementation.  Monitoring is recommended at multiple sites, including RM 28.3 (near Capay Dam), RM 26.7, RM 20.8 (near CEMEX), RM 18.8, RM 18.2 (near Moore’s Siphon), RM 17.8, RM 15.4 (near Teichert Woodland), and RM 12. Monitoring at these locations should focus on lateral channel migration, sediment deposition, and erosion.  The Cache Creek TAC Geomorphologist updated the recommendation for Huff’s Corner monitoring and continues to recommend previous evaluation and implementation actions as described below:

Recommendations from the Cache Creek TAC Riparian Biologist are grouped into four general categories: native vegetation monitoring and management, habitat restoration, invasive species monitoring and management, and special-status species.

Implementation of the Cache Creek Area Plan includes coordination and collaboration with a multitude of stakeholders including creek-side landowners; aggregate producers through the Yolo Working Group of the California Construction and Industrial Materials Association; Cache Creek Conservancy; Yocha Dehe Wintun Nation; Yolo County Resource Conservation District; Yolo County Flood Control and Water Conservation District; Yolo Habitat Conservancy; Yolo Subbasin Groundwater Agency; and various state and federal agencies.