Abstracts

Modeling the Potential for Replacing Groundwater with Surface Water for Irrigation by Using On-Farm Storage Reservoirs in the Mississippi Delta

Author(s): Thornton, R.; Pote, J.; Wax, C.

A groundwater conservation strategy is proposed in this research—the use of surface water in lieu of groundwater. This can be achieved through the construction of on-farm surface impoundments, which may be as simple as large ditches which will serve to capture precipitation and tailwater. Previous research shows the effectiveness of using stream water in lieu of groundwater on fields located within one-quarter mile of a stream, and the effectiveness of capturing rainfall in catfish ponds. This research proposes another form of surface water capture—that of on-farm storage reservoirs.

A model was developed for optimizing the size of on-site water retention structures (ditches) to capture rainfall on agricultural fields in the Mississippi Delta. The climatological driver for the model is precipitation minus evaporation, which is then adjusted by a crop coefficient to produce an irrigation demand value based on the age of the crop. The model uses long-term weather records (50 years of daily data) to estimate daily values of these climatological inputs, which are then summed to weeks through the year. Total field irrigation demand, ditch demand, ditch volume, overflow, and ground water used are outputs of the model, calculated according to specified field size and ditch volume. The percentage of required irrigation demand that is met by rain stored in the ditch is calculated weekly for the entire growing season.

Field acreage, runoff coefficient, ditch acreage, and ditch depth are interactive inputs in the model. Outputs of the model recalculate as inputs are changed. Optimization is achieved when groundwater use is minimized, annual overflow is minimized, and the smallest possible amount of the field is used for the ditch. Previous research assessed the impact of crop type and irrigation system on aquifer volume and showed that the aquifer could be reduced in volume by as much as 1,500,000 A-F over the next 50 years under current practices. This study shows that if only 10% of Delta producers adopted on-farm surface water storage for irrigation, that decline in volume in the aquifer could be reduced to 100,000 A-F over the same time period.

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Technical Sessions

1 Best Management Practices #1
2 Delta Water Assessment
3 Flood Assessment & Mgmt.
4 Wetlands
5 Watershed Mgmt. #1
6 Non-Point Source Assessment
7 Modeling
8 Water Quality
9 Best Mgt. Practices #2
10 Delta Water Conservation
11 Sedimentation
12 Storm Water
13 Watershed Mgt. #2
14 Public Water Systems
15 Surface Water Assessment & Evaluation

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