Update on Collaborative Efforts to Enhance Groundwater Recharge in the Pajaro Valley A. T. Fisher 1, C. Coburn 2, S. Beganskas 1, E. Teo 1, K. Young 1, W. Weir 1, K. Camara 2, S. Lozano 2, M. Kiparsky 3, B. Lockwood 4 1 Earth and Planetary Sciences Department University of California, Santa Cruz, CA 2 Resource Conservation District of Santa Cruz County 3 University of California, Berkeley 4 Pajaro Valley Water Management Agency Community Water Dialog Watsonville Civic Center 6 April 2017
Updates: Operating field system: stormwater collection -> MAR Regional GIS and Runoff Modeling Incentive Program for Managed Recharge Next steps (ongoing work)
Stormwater as a Source for Managed Aquifer Recharge (MAR) Low-impact development (LID) Regional spreading grounds
Stormwater as a Source for Managed Aquifer Recharge (MAR) Low-impact development (LID) 1-10 af/yr per site Distributed Stormwater Collection MAR (DSC-MAR) 10 2-10 3 af/yr per site Regional spreading grounds 10 4-10 5 af/yr per site Beganskas and Fisher, 2017
Distributed Stormwater Collection Managed Aquifer Recharge (DSC-MAR) Collect stormwater runoff (hillslope, not streams) Route, infiltrate into underlying aquifer Beganskas and Fisher, 2017
Stormwater as a Source for DSC-MAR: Example Instrumented 2011-present Precipitation Water level (culvert, basin) Infiltration rate Sediment accumulation Real-time sensor network
Stormwater as a Source for DSC-MAR: Example Project goal: 100 ac-ft/yr WY15 WY16 WY12-15 = drought WY15-16 met project goal WY14 WY12 WY13 In WY15, most rain fell in a single long storm, >100 af of runoff/infiltration! Beganskas and Fisher, 2017
Where to Place DSC-MAR Projects? to SF to SJ Composite, high-res DEM Santa Cruz Santa Cruz and N. Monterey Counties Watsonville Two main project components: (1) Spatial (GIS) analysis for MAR suitability (2) Runoff (PRMS) analysis for stormwater generation from hillslopes Moss Landing
Combining spatial data to assess MAR Suitability Compile, patch, reconcile, regrid, reproject datasets For each dataset, categorize for conditions that are more/less favorable for DSC-MAR Combine datasets to create maps showing composite suitability Schematic example: High Low Low + = High Property 1 Property 2 Higher suitability Combined
Suitability for Managed Aquifer Recharge based on Surface Conditions Considerable variation by subregion Soils and Bedrock Geology Pajaro Valley Drainage Basin
Suitability for Managed Aquifer Recharge based on Surface+Subsurface Conditions PVGB Subsurface analysis: Transmissivity (K x b) Vadose zone thickness Available storage Change in storage Composite analysis: covers a fraction of the subregion where there are subsurface datasets
Where to Collect Stormwater Runoff? Hydrologic response units (HRUs) defined by topography HRUs = 0.1 to 1.0 km 2 (25 250 acres) Pajaro Valley Drainage Basin High resolution! PVDB
Mean annual precipitation 65 in 0 in Precipitation Runoff Dry Normal Wet Mean annual runoff 14 in 0 in
Vegetation density Percent impervious Percent sand Example PRMS parameters Dry Normal Wet Runoff Mean annual runoff 14 in 0 in
Next steps: combine mapping & modeling + MAR suitability Assess existing and planned sites Help to identify and assess new sites Runoff availability http://www.rcdsantacruz.org/managed-aquifer-recharge
Screening DSC-MAR project locations PVGB Currently active MAR suitability + Runoff availability
Screening DSC-MAR project locations Currently active PVGB Prospective MAR suitability + Runoff availability
Costs to Growers/Landowners for DSC-MAR Land taken from production/reduced access Maintenance of infiltration structures (basins, dry wells) Harkins Slough MAR basin (PVWMA) scraped Fine sediment unscraped How can participation be incentivized?
There is a Workable Template: Net Energy Metering generate energy locally account for net usage excess power goes on the grid for sale (and eventual use) Requires: reliable measurement and accounting formula to calculate benefit/rebate stakeholder and agency trust
Example: Net Recharge Calculations Irrigated area: 75 irrigated acres Applied water: 2.5 ft Annual precipitation: 1.5 ft (18 inches) Runoff/precipitation = 0.4 (appropriate for intense events) Options: Drainage: Infiltration: 200 400 600 acres 2 4 6 acres Augmentation fee = $203/ac-ft (outside of Delivered Water Zone) Recharge Net Metering rebate: 50% of net infiltration
Example: Net Recharge Calculations Net metering Net pumping: 188 ac-ft Corrected for incidental recharge 61 61 194 Net pumping < 0: infiltration > pumping More collection More infiltration
Example: Net Recharge Calculations 2 4 6 Infiltration basin size (ac) 188 ac-ft pumped More collection More infiltration
Recharge Net Metering (ReNeM) in the PVGB (five-year pilot program, 10/2016-9/2021) Goal: ~1000 ac-ft/yr (8-10 field projects, each 100 ac-ft/yr) Third-party certifier (TPC) identifies sites, raises capital, develops engineering, plans/builds for measurement TPC works with landowners/tenants to validate TPC certifies performance, reports to agency Agency applies formula to calculate rebate (= credit/check ) Current status One site is operational, one approved for funding (90% design), two more are in development/permit Multiple requests for site consideration For ReNeM pilot: RCDSCC and UCSC are the TPC
Recharge Net Metering (ReNeM) three kinds of support Capital costs site ID, design, engineering, installation Validation measurements, sampling, certification Rebates (Incentives) offset for operation and maintenance costs In the PVGB: ReNeM costs are competitive Support is self-reinforcing
Recharge Net Metering (ReNeM) is not Groundwater Banking An aquifer is a bank like a colander is a bucket ReNeM is different: Incentivizes infiltration, not recharge, not storage No water ownership/right is claimed, no recovery is promised Rebate is performance based, year by year Incentive based on a rebate of fees
Summary and Opportunities Stormwater is a valuable resource, useful for recharge We need to find best places to locate projects, design and operate systems to measure performance Improve water quality along with supply (ask me how) Groundwater recharge provides hydrologic system services, justifies incentives Collaboration is critical. Dependence cooperation
Regional Flow Thank you! Questions? Funding:
California's GW Supplies Face a Triple Threat Regional Flow Less GW Recharge Increasing demand Shifting land use More intense rainfall
Pajaro River and Pajaro Valley Groundwater basins PVGB, lower PR basin, mostly Santa Cruz and northern Monterey Counties Primary fresh water resource is groundwater PVWMA: Special Act district (1984) PVWMA serves 70,000 acres, 30,000 irrigated Major crops: Strawberries, cane berries, table crops, organic (30%) $1B farm revenue
Groundwater overdraft: a regional challenge Overdraft: ~12,000 ac-ft/yr ~20% of pumpage SW intrusion on coast No water imports Management plan: Conservation Recycling Managed recharge Augmentation fees: $203/ac-ft - metered $258/ac-ft - metered, DWZ * $359/ac-ft - delivered * DWZ = Delivered Water Zone PVWMA Service area PVWMA, 2016
Project Extent and Basin Subareas Santa Cruz and northern Monterey Counties Four topographic basins Runoff modeling: SLRB and PVDB (MSCC soon )