Irrigation in the Mississippi Delta: History and Future

1. Irrigation in the Mississippi Delta: History and Future

2. Mississippi Delta (not the MS River Delta)

3. Lower Mississippi River Flood Plain Altered • Logged, drained, channelized • Levees built • Land Characterization: • > 80% Agriculture • Row crops • Rice • Aquaculture • Primary concerns for sustainability: • Water Quality • Water Availability • Mississippi River Flood Plain prior to landscape modifications for agriculture • Land Characterization: • Bottomland hardwood wetlands • Annual flooding distributes nutrient-rich matter • Artesian conditions in underlying alluvial aquifer

4. Arkansas 50-150 ft Louisiana Mississippi Alluvial Aquifer Alluvial extent • Agriculture / Irrigation • 3rd most intensively used aquifer in US in 2000 • MS 2nd largest user behind AR MS Alluvial aquifer Cone of Depression Gravel/Sand

5. Irrigation a Necessity Mississippi River Alluvial Aquifer • Irrigation is necessary in the Delta to reach optimum productivity • 28% of annual precipitation • 4 billion gallons per day • Flow in Delta streams is at or near baseflow during the growing season (May-August) • Unknown amount comprised of irrigation return flow The Bogue Phalia (a northwest MS River) at lowest flow in July 2009

6. What are the results of irrigation on water availability?

7. Declining Water Levels ~1 ft per year decline Water-level altitude , in feet above sea level

8. Storage and base flow loss

9. Why is groundwater important for aquatic ecosystems? • Groundwater/Surface-Water Exchange Benefits: • Sustains baseflow in streams • Bank storage dampens overall flood impacts • Streambank stabilization – supplies moisture to riparian vegetation • Temperature regulation for aquatic biota • Supplies nutrients and inorganic ions to stream • Buffer the transport of contaminants through the streambed interface

10. Why is groundwater important for aquatic ecosystems? Stream/Aquifer in Connection Stream/Aquifer not in Connection -Increased flow in stream -Decreased deposition of fine sediments -NO3 concentrations in stream reduced -Stream recharges alluvial aquifer -Decreased flow in stream -Increased deposition of fine sediments -NO3 concentrations in stream concentrated -What are the affects on recharge? Losing Stream Anaerobic conditions in aquifer promote denitrification Disconnected Stream Gaining Stream GW dilutes NO3 in stream

11. What are the results of irrigation on flow paths through the aquifer?

12. A Complex System

13. How have water-level declines changed the condition of the alluvial aquifer? Confined Conditions in 1870 (Predevelopment) Water-Table Conditions in 2007 Discharge to wells -2.19 Recharge 0.307 Recharge 0.066 Mississippi River -0.002 Mississippi River 0.011 Bluff Hills 0.052 Bluff Hills 0.035 Stream Leakage -0.192 Stream Leakage 0.120 Underlying Units 0.095 Underlying Units -0.022

14. What are the Effects of Conservation (Management) on these Flow Paths in the Future?

15. How will flow in the alluvial change in the future? Objectives • Employ existing regional flow model to assess future groundwater supply • Develop water use conservation scenarios that vary in amount and distribution • Assess the effects of amount and location of water use conservation

16. MS Delta Conservation Scenarios, 2010 - 2038 Cone of Depression Area (approx. extent) Water- Use Reduction (%)

17. Change in Storage

18. Base Flow

19. How Can We Better Monitor Water Resources?

20. Study Objective Assess the role of groundwater/surface-water exchange on the transport of nutrients in the northwestern MS Assess the feasibility of monitoring groundwater/surface-water exchange at existing streamgaginglocations Near-stream piezometers installed July 2010 near existing stream gages Big Sunflower at Clarksdale Big Sunflower at Sunflower Big Sunflower at Anguilla Existing Gage House: Stage , Conductance, and Stream Temperature Real-time coupled groundwater streamgaging stations West East DCP to relay transducer data Deck for access during high flow ~100’ 41.5’ Pressure Transducer: Head Conductance, and Temperature *not to scale

21. Big Sunflower at Sunflower coupled groundwater/surface-water gage Existing Gage House: Stage , Conductance, and Stream Temperature West East DCP to relay transducer data Deck for access during high flow Losing Conditions: Groundwater Level < Stream Stage 41.5’ ~100’ Pressure Transducer: Head Conductance, and Temperature *not to scale

22. Affects of unsustainable groundwater withdrawals on the MS Delta • Loss of baseflow to streams • Groundwater is pumped into streams to sustain flow - cost $$ and could exacerbate current water situation • During the growing season, irrigation return flow can make up most of the water in streams • Overuse of surface-water for irrigation has resulted in recent fish kills

23. Affects of unsustainable groundwater withdrawals on the MS Delta • Increased recharge from the surface • Increases the vulnerability of the aquifer to surface contamination • Recharge is still not sufficient to replace withdrawals

24. Affects of unsustainable groundwater withdrawals on the MS Delta • Future concerns over water supply for irrigation • State initiated Conjunctive Water Use task force • Dissension over who actually is part of the problem – within the cone of depression versus outside of the cone of depression • Amount of irrigated acreage increasing each year along with new permits for groundwater and surface-water irrigation

25. Questions?