Watershed Water Resource Assessment in the Cache River Critical Groundwater Area for Future Targeting of Conjunctive-Use and Conservation Projects AWRA 2018 – GIS & WATER RESOURCES X Orlando, FL April 23, 2018 Mary A. Yaeger, Joseph H. Massey, Michele L. Reba, M. Arlene A. Adviento-Borbe Overview • Background – motivation • Water resource assessments . Study objectives • Hydrologic assessment of study region . Gauged streamflow . Precipitation • Geospatial data assessment of study area – HUC12s . Preliminary results Importance of Agriculture in Arkansas • Arkansas agricultural production . High % of GDP . 1 of 6 jobs . #1 in Rice Production . #3 in Cotton Production . Top 25 for 24 commodities Irrigation in the Mississippi Delta Region • ~80% irrigation water comes from the Mississippi River Valley Alluvial Aquifer (MRVAA) . The MRVAA is 2nd only to High Plains aquifer in irrigation withdrawals (Maupin and Barver, 2005). Mississippi River Valley Alluvial Aquifer Nebraska 8.297 M ac California 7.862 M ac 8.016 M ac Texas 4.489 M ac 5.010 M ac Map credits: USDA NASS; USGS National Atlas of the U.S. Agriculture, Precipitation, & Irrigation 0 200 Miles Irrigated Land - Change in Acreage: 2007 to 2012 2 0 1 2 1 Dot = 1,000 Acres Increase C e 1 Dot = 1,000 Acres Decrease n s u s o f A g r 0 100 i c u United States Net Decrease 0 100 l Miles t -777,074 u 12-M081 r Miles e U.S. Department of Agriculture, National Agricultural Statistics Service Critical Groundwater Areas (CGAs) in Arkansas MRVAA • Unsustainable pumping • Two cones of depression • Critical groundwater areas • South: Grand Prairie CGA . Two large rivers . Irrigation diversions. • North: Cache River CGA . No large rivers Water Resource Assessments • Done for entire states, and sometimes large river basin . AR, MS, AL, others . HUC4, ~17,000 sq mi • Example: AR has 8.7 mil AFY excess surface flow . (AR Water Plan, 2014) • This amount is not evenly distributed in space! . Grand Prairie and Cache River CGAs • Need water resource assessments at sub-watershed scale. (HUC12, ~40 sq mi) General Study Objectives • Watershed water resource assessment . HUC12 scale • Identify suitable potential sites for . Surface water development On-farm irrigation reservoirs In-stream weirs . Conservation / management practices Multiple-inlet rice irrigation Alternate wetting/drying irrigation Land into CRP or other conserved use Watershed Water Resource Assessment • Analyze geospatial data sets . NAIP, Landsat . NASS CDL, SSURGO, DEM . NHD, NHDPlus • For in-stream weirs . Stream reach Straight length Channel slope • For reservoirs and conservation set-asides . Low productivity . Low elevation . Poorly draining soils, etc. Study Region Hydrology • Project subwatersheds: 3 HUC8s bordered by Crowley’s Ridge . Cache River . L’Anguille River . Big Creek. • Study area in upper reaches of these systems. Cache River and Big Creek Tributaries of the White River to west . L’Anguille River Tributary of the St. Francis River to east Study Region Hydrology • Cache River – long, skinny watershed . Bayou DeView – tributary separate from mainstem in study area • L’Anguille River – small contributing area • On average from 1998 – 2017: . Upper Cache gauge: ~679,000 AFY, from contributing area of 701 sq mi. Lower L’Anguille gauge: ~770,000 AFY, from contributing area of 786 sq mi Study Area Hydrology: Variation Within the Year • Steamflow seasonality . Dec – May: high flow . Jun – Nov: low flow • October: lowest flow in both rivers . Cache upstream: highest average monthly low flow. Monthly average precipitation and water yield (mm) 1998 – 2017 Study Area Hydrology: Daily Flow (FDC) • L’Anguille River, upstream, downstream . Highest daily flows, relative to drainage area • Cache River, upstream . More “flashy” . Mainstem extensively straightened Flow Duration Curve: All daily water yields for 20 years arranged from highest to lowest. Agriculture in Study Region • Mainly rice and soybean. Some corn and cotton, mostly in the south and east • Rice, soybean, corn, and cotton . Most likely to be irrigated Study Area and Cone of Depression •Study area • 54 HUC12s in the Cache River CGA. Study Area Sub-watersheds • HUC12s in 4 main counties over the cone of depression. • County portions west of Crowley’s Ridge: . Craighead . Poinsett . Cross . St Francis Study Area Topography • Quite flat . Except for Crowley’s Ridge to the east. • Elevation ranges from 162 – 51 m . • Elevation drops in the south in lower L’Anguille and headwaters of Big Creek. Hydrologic Study Area Soils Group Drainage Class • Alfisols dominant • Mainly silt and silt clay loams • Hydrologic group C/D and D • Soil drainage classes: somewhat poorly – poorly drained 2006 2015 Agriculture: 10 Year Comparison • Rice and soybean are dominant crops . Soybean = 3 times the acreage of rice. • Corn and cotton . Grown south, and east along the Ridge. Rice Agriculture: 10 Year Soybean Average Area • Rice acreage . North and western portions of the study area. • Soybean acreage . High % in most HUC12s Surface Water Use: Reservoirs • 143 on-farm irrigation reservoirs . Within boundaries of Cache River CGA . HUC12 average area is ~21,000 acres • On average: . ~35 acres per reservoir . ~2.6 reservoirs per subwatershed • Variable sizes, placement . 2.5 to 309 acres per reservoir . 0 to 12.5 reservoirs per subwatershed NHD High Resolution Flowlines • Cache River HUC8 . Higher percentage of ridge headwaters • Upper Cache River mainstem . Straightened extensively • L’Anguille River mainstem . Ridge headwaters to east . Extensive ditch network to west NHD High Resolution Flowlines • Reservoirs all near ditch or stream. • Over the deepest cone of depression • Small ditches • Headwaters NHDPlus Flowlines Slope Stream order • Channel slopes are fairly flat. • Mostly 1st • Extensive ditch network. and 2nd • Lacking discharge order measurements streams Reservoir Ranking # Upstream Reservoir Reservoir Miles 1st Miles 2nd Reservoir ID Upstream Order Up Order Up ID R1 R1 0 2.0 0.0 R2 1 7.6 0.0 R1 R3 2 8.7 0.0 R1, R2 R4 0 2.0 0.0 R5 4 14.2 1.6 R1, R2, R3 R6 0 3.6 0.0 R2 R3 • About half of existing on-farm reservoirs R4 are on 1st and 2nd order streams. • How many reservoirs are upstream of planned R5 R6 location? • How many miles of 1st and 2nd order stream is available for possible supply? Sub-Watershed Ranking • Rank HUC12s by . Stream order . Channel slope . Crop mix (% rice acreage?) . % aquifer saturation • Weir locations best on streams . Order 3 or higher . Flat channel slopes . “Long, skinny” sub-watersheds • Benefit more farms/mile Summary: In Eastern Arkansas • Annual precipitation ~50 inches, major rivers • Most agriculture is groundwater-irrigated • Depletion of the MRVAA aquifer . Unsustainable pumping • Uneven distribution of surface water resources • In time – precipitation not always when it is needed • In space – excess streamflow not always where it is needed Summary: Study Area • Flat, highly modified landscape, rice/soybean rotation • Poorly draining soils with lower confining clay layer . Holds water in rice paddies . Prevents recharge from precipitation • Mostly 1st and 2nd order streams . Cone of depression Summary • Need to reduce groundwater usage in area with intensive groundwater irrigated agriculture. • HUC12 watershed water resource assessments can . assist managers in resource allocation decisionmaking . target conservation methods and surface water development to areas where they provide most benefit Not all HUC12s are suitable for the same methods. • Project will develop methodology for practical use. • “Precision conservation” Questions?.