Agricultural groundwater banking: surface water availability & on-farm research

Transcription

1 Agricultural groundwater banking: surface water availability & on-farm research Helen Dahlke, Tiffany Kocis, Andrew Brown, Toby O Geen, Steve Orloff, Dan Putnam, Astrid Volder, Ken Shackel FEBRUARY 22, hdahlke@ucdavis.edu Signs of the 5 year drought ( ) Reservoir Status February, 2015 U.S. Drought Monitor December, 2016 Tree mortality August 18, Source: conditions/ 1

2 Water Supply and Climate Climate change and loss of snowpack reduce surface water availability and increase need for alternative storage Long-term groundwater overdraft in the Central Valley is ~ 2 km 3 /yr SNOWPACK RESERVOIRS Source: UCCHM, 2014 AGRICULTURE, ENVIRONMENT, URBAN 3 Opportunities for water management U.S. Drought Monitor January, in 2 month 4 Source: conditions/ 2

3 Rainfall and streamflow conditions Real-time streamflow conditions 5 Source: conditions/ Sierra Snowpack vs Winter Temperature April 1 Snowpack Percent of Average From California Cooperative Snow Surveys Reservoir Rule Curve Flood Control Pool Conservation Pool 6 Sierra Winter (DJF) Average Minimum Temperature (degrees Fahrenheit) Courtesy Mike Anderson (DWR) 3

4 Forms of groundwater recharge Natural recharge from wetlands, flooding Infiltration basins On-farm flood flow capture Aquifer Storage and Recovery 7 Agricultural Groundwater Banking Farmland is flooded during the winter using surface water to recharge the underlying groundwater Large spreading areas are needed to capture runoff from few (6-10) storms 8 million acres of irrigated farmland could serve as spreading grounds Existing irrigation infrastructure could be used to move water from streams and reservoirs to farmland for recharge 8 4

5 Crop Suitability for ag-recharge: alfalfa, almonds Alfalfasupports $7.6 billion dairy industry In 2013 largest acreage crop in CA (~ 1 million acres) high likelihood to find land on suitable soils Relatively low use of fertilizers, pesticides low risk for leaching Flood irrigation with surface water most common (75%) allows fast spreading of large water amounts Conducted flooding experiments in two locations in winter of 2014/15; repeated experiments in Scott Valley in 2015/16 CALIFORNIA Almond industry has $21.5 billion in total economic output, provides 97,000 jobs climate adaptation tools needed to create sustainable, long-term water supply 9 On-Farm recharge experiments - alfalfa Three winter water application rates: Continuous every day High 3-5 water applications per week Low 1-3 water applications per week Standard - no winter water application Use soil water balance model to estimate deep percolation and losses to evapotranspiration and soil storage Soil water balance model Scott Valley, Siskiyou County, 15 acre field AWC = available water content 11 5

6 On-Farm recharge experiments - alfalfa 2014/15 dry year: Early dry-out in standard plot 2015/16 Above normal year: Late dry-out Recharge increases plant available water Loss to ET, soil storage is 1-7% Continuous: 26 ft recharge Continuous: 11 ft recharge No benefit for plant available water Loss to ET soil storage is 1-2% Total recharge was 135 AF Total recharge was 107 AF 12 On-Farm recharge experiments - alfalfa Water table rose up to 6 ft in response to winter recharge Application of up to 26 ft of water caused no discernible difference in alfalfa yield 13 6

7 On-Farm recharge experiments - almonds Application of 60 cm (2 ft) of water in Dec.-Jan. Root zone remained saturated up to 48 h after recharge events Fine sandy loam Sand 14 On-Farm recharge experiments Tree stem water potential (SWP) indicates that trees in the flood treatment remained more hydrated than the control trees There were no statistically significant differences in yield (Nonpareil almond variety) Fine sandy loam Sand stress 15 7

8 High-magnitude streamflow assessment for groundwater recharge Historical daily streamflow records for 93 stream gauges (13 unimpaired, 80 impaired) 90 th percentile used to designate highmagnitude flows (HMF), determined from full historical record Metrics: magnitude, duration, frequency and timing Analysis is conducted for different time periods (annual, Nov Apr, Dec Feb) and record lengths (Sac Valley: , San Joaquin Valley: ) 16 High-magnitude flows for groundwater recharge Average total flow above 90 th percentile Outlet Dec-Feb Nov-Apr Sac Valley 1.15 MAF 1.88 MAF SJ Valley 501 TAF 972 TAF A single, average wet year in the Sacramento Valley can provide two-times the annual groundwater overdraft. 30% of years are wet ; 3 MAF from Nov-Apr Freeport, CA Delta is in excess conditions (no quality or quantity concerns) more frequently than flow conditions reach the 90 th percentile 41% of days since 1976 in true excess 8% of days, flow was above the 90 th percentile Vernalis, CA Kocis & Dahlke, ERL, submitted 17 8

9 Caveat True Availability of High-Magnitude Flows, Timing, Frequency Number of years with HMF Number of HMF days per time period Number of peak events 18 Streamflow Availability Rating for Recharge (STARR) STARR index indicates the most suitable watersheds for ag-recharge in terms of water availability 1. Generated maps of the following metrics: V/A = HMF volume / watershed area D/P = Average number of HMF days / number of days in period YWF = fraction of years with HMF 2. Weighted index of surface water availability: STARR = 0.61 (YWF) ( ) ( ) 3. STARR values were divided into 6 equal-interval classes: excellent poor surface water availability 19 Kocis & Dahlke, submitted 9

10 Soil Agricultural Groundwater Banking Index (O Geen et al. 2015, CalAg) 20 Good groundwater banking locations? Soil characteristics: Hydraulic conductivity Occurrence of restrictive layers Topographic Limitations (slope) Chemical Limitations Surface Condition (e.g. crusts, erodibility)

11 Conclusions Alfalfa, almonds, pecans are promising crops if grown on suitable soils with high percolation rates In some alfalfa fields 26 ft of water could be recharged in 30 days without decline in yield High-magnitude flows potentially provide an untapped source of water during the winter months Short duration events and low frequency of highmagnitude flows suggests a need for coordinated efforts for the local-scale utilization Agricultural groundwater banking can increase instream flows, help mitigate floods, and improve groundwater supply for disadvantaged communities 22 THANKS!! hdahlke@ucdavis.edu Acknowledgments: Many thanks to Steve Orloff, Allan Fulton, Dan Putnam, Roger Duncan, David Doll, Nicole Stevens, Jim Morris for help and logistical support