Receive and file the 2022 Cache Creek Annual Status Report (No general fund impact) (Lindbo/Sabatini)

 

BACKGROUND

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 the creek.  The CCRMP provides a policy framework for the restoration of 14.5 miles of Lower Cache 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 status 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.  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 2022 Water Year which covers the period of October 1, 2021, to September 30, 2022 (Attachment A).  

SUMMARY OF 2022 WATER YEAR FINDINGS

Hydrologic and Water Quality Findings

The 2022 Water Year was a very dry year for Cache Creek and the Sacramento Valley.  Drought conditions persisted throughout the water year.  An unusual early storm occurred in late October 2021 generated flows of approximately 4,400 cubic feet per second (“cfs”) at Rumsey and 2,800 cfs at Yolo.  These flows represent only approximately 25% of a 2-year return interval peak.  Additional small storms occurred in December 2021, but no additional flows occurred during the entire water year.

Geomorphology Findings

Water Year 2022 was slightly wetter than 2021 in the Cache Creek basin, but still very dry relative to long term hydrologic conditions.  The October 2021 peak flow at the Yolo was well below the threshold of 20,000 cfs required for significant sediment transport and channel change.  These low flow conditions contributed to the seventh-lowest delivery and transport of sediment to, and through, the CCRMP area over the last 18 years.  As a result, the only measurable channel change in Cache Creek in Water Year 2022 was the continued persistence and accelerated expansion of riparian vegetation in and along the channel that established after the extremely wet Water Year 2019.  This vegetation succession has continued through three years of extremely dry conditions.

Because of the limited and localized channel change in Water Year 2022, the recommendations developed by the Cache Creek TAC did not change substantially from recommendations made in 2017, 2018, 2019, 2020, or 2021.  These recommendations are now six years old and should be carefully reviewed in Water Year 2023, as the accumulated buildup of vegetation in the Cache Creek channel will eventually be inundated by higher flows in future wetter years.

Biological Resources Findings

The condition of native vegetation in 2022 was generally similar to conditions observed in 2021, with four notable exceptions.  First, continued increase of in-channel vegetation was observed in some of the same locations observed during the 2021 Creek Walk, as expected given the lack of significant scouring flows during the 2021–2022 winter season.  Although some formerly vegetated areas that were scoured during the 2016–2017 winter season high flows have yet to recover, other areas are now densely vegetated. Second, there was more significant evidence of drought-stressed vegetation in both areas noted in 2021 and additional areas observed in 2022. Third, there were encouraging signs of native vegetation recovery in some areas heavily impacted by off-highway vehicle (“OHV”) use in recent years. Lastly, native herbaceous vegetation appeared to be increasing adjacent to pools created by intact beaver dams in several locations.
 
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 are potentially re-establishing and spreading in some locations.  However, one of the most significant observations in 2022 was that arundo and tamarisk are being effectively treated in many locations due to increased efforts by Cache Creek Conservancy staff. 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 volunteer observers during the 2022 Creek Walk.  Swainson’s hawks (State threatened) were observed in five of the seven reaches, and an occupied nest was observed in the Dunnigan Hills Reach. Western pond turtles (State species of special concern) were observed in deeper pools in the Capay, Guesisosi, and Dunnigan Hills reaches; several pools appeared to be the result of significantly increased beaver activity observed in 2022 compared to recent years.  No riparian bank swallows (State threatened) were observed, although bank habitat suitable for nesting colonies was checked starting at river mile ("RM") 26.2 in the Hungry Hollow Reach and at numerous locations further downstream. A total of 74 unique bird species were observed in 2022 including acorn woodpecker, American kestrel, Bullock’s oriole, common gallinule, lesser nighthawk, marsh wren, Northern harrier, phainopepla, red-shouldered hawk, red-tailed hawk, song sparrow, white-tailed kite, and wood duck.  Other wildlife species observed included Columbian black-tailed deer, black-tailed jackrabbit, California ground squirrel, river otter, Western whiptail, and fishes including bluegill, common carp, green sunfish, and largemouth bass.
 
Significant opportunities for habitat enhancement and restoration are essentially unchanged from 2019, including upland areas on the north bank from 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), the Moore Siphon repair site (RM 18.0), 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 off-channel pits in the Dunnigan and Hoppin reaches (e.g., on the north bank from RM 15.0–15.4).  Based on 2017 and 2018 Creek Walk observations, the long-term resilience of revegetation and restoration projects within or adjacent to the active channel should be carefully considered prior to implementation, since such projects can be negatively impacted or completely removed by high flows.  Passive restoration (e.g., streamflow enhancement and invasive species treatment) may be a more cost-effective approach for in-channel or near-channel locations subject to high flows.

SUMMARY OF 2022 WATER YEAR RECOMMENDATIONS

Hydrologic and Water Quality Recommendations

The CCTAC Hydraulic Engineer recommends the following:

Geomorphology Recommendations

As in previous years, Water Year 2022 recommendations from the Cache Creek TAC Geomorphologist regarding geomorphology 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 continues to recommend the following evaluation and implementation actions:

Biological Resources Recommendations
 

Recommendations regarding biological resources 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, the aggregate producers, the Cache Creek Conservancy, the Yolo County Resource Conservation District, the Yolo County Flood Control and Water Conservation District, the Yolo Habitat Conservancy, the Yolo Subbasin Groundwater Agency, and various state and federal agencies.