Background
The Cache Creek Area Plan (CCAP) was adopted by the Yolo County Board of Supervisors in 1996. The CCAP is comprised 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 on-going 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 comprised of a hydraulic engineer, a fluvial geomorphologist, and a riparian biologist. The Cache Creek TAC was etablished 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 Paul Frank, P.E., CED (Hydraulic Engineer), Mark Tompkins, P.E., Ph.D (Fluvial Geomorphologist), and Andrew Rayburn, Ph.D (Riparian Biologist).
Section 2.2 of the CCIP requires that the Cache Creek TAC produce an annual status report in January of 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) indentify recommendations and projects to be implemented the next 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 2020 Water Year -- the period of October 1, 2019 to September 30, 2020 (Attachment A). A public comment version of the draft annual report was released for a 14-day public comment period on December 21, 2020. Staff received two public comments (Attachment B) and addressed the comments in the annual report, as appropriate.
Summary of Findings
Hydrologic and Water Quality Findings
The 2020 Water Year was a dry year for Cache Creek and the Sacramento River Valley. There were few storm events that produced runoff and, in fact, peak storm flows at Rumsey never reached the typical irrigation season flows in the Creek.
Water quality sampling data remained within or below the ranges measured in previous years. Some contaminants continued to not be detected in Water Year 2020 as in the last several years.
Geomorphology Findings
Water Year 2020 was much drier than 2019 in the Cache Creek basin. The peak flow at the Yolo USGS streamflow gage only reached 449 cubic feet per second (cfs), well below the threshold required for significant sediment transport and channel change. These low flow conditions contributed to the second lowest delivery and transport of sediment to, and through, the CCRMP area over the last 16 years. As a result, the only measurable channel change in Cache Creek in Water Year 2020 was the persistence and expansion of riparian vegetation in and along the channel that established after the extremely wet Water Year 2019.
Because of the extremely limited channel change in Water Year 2020, the recommendations developed by the Cache Creek TAC did not change substantially from recommendations made in 2017, 2018, or 2019. These recommendations are now four years old and should be carefully reviewed in Water Year 2021, especially if extremely wet or extremely dry conditions occur in Water Year 2021.
Biological Resources Findings
The condition of biological resources in 2020 appeared to be similar to conditions observed in 2019, although only select locations were visited due to the modified approach to the 2020 Creek Walk due to the COVID-19 pandemic. Continued growth of native and non-native woody and herbaceous vegetation was observed in some locations observed during the 2019 Creek Walk, as expected given low flows during the 2019–2020 winter season high flows. 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.
Non-native and invasive species appear to remain widespread along lower Cache Creek, although the intensive treatment of arundo, ravennagrass, and tamarisk that has occurred since 2006 with funding from the Wildlife Conservation Board has greatly reduced the extent of these three species. As in 2019, arundo, tamarisk, and other non-native species such as purple loosestrife and water primrose were observed to be re-establishing and potentially spreading in some locations. 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. 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 and Cache Creek Conservancy staff during the modified 2020 Creek Walk. Swainson’s hawks (State threatened) were observed in six of the seven reaches, and a Northern harrier (State species of special concern [SSC]) was observed in the Madison reach. No Western pond turtles (SSC) or colonies of riparian bank swallows (State threatened) were observed, likely due to the reduced number of locations visited during the modified 2020 Creek Walk. It should be assumed that both species are still present along lower Cache Creek. Including Swainson’s hawks and Northern harrier, a total of 40 unique bird species were observed in 2020 including red-tailed hawk, red-shouldered hawk, osprey, acorn woodpecker, Bullock’s oriole, song sparrow,least sandpiper, and wood duck. Other wildlife species observed included Columbian black-tailed deer, desert cottontail, Mexican free-tailed bat, and non-native common carp.
Significant opportunities for habitat enhancement and restoration are essentially unchanged from 2019, including the PG&E “Palisades” site (river mile [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-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. 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) may be a more cost-effective approach for in-channel or near-channel locations subject to high flows.
Summary of 2020 Recommendations
Hydrologic and Water Quality Recommendations
The Cache Creek TAC Hydraulic Engineer recommends the following:
- Capay Dam – Remedies to prevent future damage of the dam and movement of the dam’s concrete pads into the channel should be undertaken. Additionally, erosion behind the recent emergency bank stabilization wall should be investigated and addressed.
- PG&E Palisades – The erosion control blanket and all associated infrastructure be removed and the palisades either be removed entirely or cut at or below ground level and revegetation/natural stabilization project be implemented. PG&E is working on design plans to implement this.
- Erosion sites identified (Jensen Bend, Granite Esparto, Esparto Bridge, south bank of RM 23.3, Teichert Esparto, Payne Property, and Woodland Reiff) should continue to be monitored in the future.
- Longitudinal profiles of water surface elevations should be performed in the future to assist in calibrating the hydraulic model of Cache Creek developed in 2016 and updated in 2018. The Cache Creek TAC Hydraulic Engineer recommends mobilizing for survey for a predicted flow in excess of 30,000 cfs if observed in the winter of 2020-2021.
Geomorphology Recommendations
As in previous years, geomorphology recommendations for Water Year 2020 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:
- Accelerate voluntary implementation of previously recommended bar skimming projects at RM 24.6 – 25 and RM 20.1 – 20.5.
- Reinitiate voluntary bar skimming project evaluation at RM 21.6.
- Evaluate the potential for additional bar skimming at RM 21 and RM 22.
- Complete removal of the PG&E Palisades infrastructure from Cache Creek at RM 26.9
- Notify bridge owners of scour and deposition at bridge piers and abutments, and continued succession of riparian vegetation upstream and downstream of bridges.
- Continue detailed monitoring and assessment of channel treatments at locations of 2017 channel migration and erosion (RM 26, 25.5, 23.5, 22, 21.5, and 18).
- Continue detailed monitoring of fine sediment deposition at Huff’s Corner and complete an evaluation of the need to remove deposited fine sediment.
- Following the 2019 approval of the CCAP Update, assess Channel Form Template (CFT) with respect to 2019 topographic conditions at RM 26.0, RM 25.5, RM 23.5, RM 22, RM 21.8, RM 21.4, RM 18.2, and anywhere else the active channel has migrated near or beyond the CFT. Also, complete administrative and/or technical changes to the CFT based on the results of this assessment.
- Yolo County, Cache Creek TAC, Cache Creek Conservancy, Yolo County Resources Conservation District, and Yolo County Flood Control and Water Conservation District should work together to develop a comprehensive invasive species removal, ecosystem restoration, flood management and water supply bundle of projects based on prior Cache Creek TAC recommendations and submit additional Proposition 1 (and other) grant proposals to fund such projects in Water Year 2021.
Biological Resources Recommendations
Recommendations regarding biological resources are grouped into four general categories: native vegetation monitoring and management (Section 5.1.5), habitat restoration (Section 5.2.3), invasive species monitoring and management (Section 5.3.2), and special-status species (Section 5.4.2).
- Recommendations regarding native vegetation focus on monitoring approaches intended to understand changes in native vegetation, as well as management actions required (if any) to maintain desirable flow conditions.
- Recommendations regarding habitat restoration highlight high-priority potential projects, the importance of including native understory species, the need for post-implementation monitoring, the importance of planting native species on invasive species treatment sites, and the potential for increased surface flows and strategic channel maintenance projects to accelerate native habitat recovery.
- Recommendations regarding invasive species monitoring and management include expanding the list of priority species and the areas in which treatments are implemented, the importance of a formal monitoring program to track invasive species, the need to remove treated biomass from the CCRMP area, the importance of planting native species on invasive species treatment sites, and the ongoing need to leverage invasive species treatment within the CCRMP area to support additional mapping and treatment upstream of Capay Dam.
- Recommendations regarding special-status species focus on the need for additional monitoring and documentation of both rare and common species, documentation of observations, and the potential for increased surface flows to benefit Western pond turtles and other native species.
Program Highlights
The following noteworthy events occurred during the 2020 calendar year:
Four public Cache Creek Technical Advisory Committee (TAC) meetings were held: February 24, 2020, March 31, 2020, August 11, 2020, and August 26, 2020. Due to the COVID-19 pandemic, the latter three meetings were held virtually. The meetings were attended by County staff, members of various partner agencies, program stakeholders, and the public.
The Cache Creek TAC conducted its 2020 Creek Walk on July 15 & 16, 2020. The Creek Walk is the annual physical inspection of the creek with the main purpose of documenting channel conditions, as required by the CCIP. Due to the COVID-19 pandemic, Creek Walk participation was limited to only the Cache Creek TAC, Natural Resources Division staff, and a select handful of consultants and program stakeholders. The logistics of the Creek Walk were also modified to adhere to social distancing guidance. Creek Observations made by the Cache Creek TAC during 2020 Creek Walk are provided as Appendix C of the Annual Report.
The Cache Creek Parkway Plan – Open Space Inventory and Baseline Improvements document received local and state-wide recognition from the American Planning Association, being awarded with a 2020 Award of Excellence in the category of Implementation Award for Small Jurisdiction from both the Sacramento Valley Section and California Chapter!
In Spring 2020, the Natural Resources Division posted the Draft Cache Creek Parkway Plan – Master Plan & Parkway Vision to its website. Staff was intending to schedule as series of public workshops on the document during the 2020 calendar year; however, those plans have been put on hold due to the COVID-19 pandemic.
On October 6, 2020, the Board of Supervisors approved the schematic designs for a new visitor center, administrative building, and storage facilities at the County-owned Cache Creek Nature Preserve property. The schematic designs can be found in Annual Report Appendix I.
Dr. Darrel Slotton (County consultant) and the Natural Resources Division finalized three reports related to the OCMP Mercury Monitoring. All three reports are from 2018 sampling events performed by Dr. Slotton and his team from UC Davis. The reports can be found in Annual Report Appendicies D (2018 Mercury Monitoring), E (2018 Water Column Profiling), and F (2018 Bottom Sediment Collection). |