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Goal: Apply Knowledge Globally Estimating the Ratio of Pond Size to Irrigated Crop Land: A Tool to Conserve Groundwater Resources in Mississippi

Measurement equipment in front of a body of water

Accurately sized water storage ponds can help to improve the efficiency of groundwater pumping. Photo by USDA Forest Service.

Introduction

Groundwater withdrawals in the Mississippi Delta region and around the nation have increased dramatically since the last century resulting in the depletion of water resources from subsurface aquifers. Groundwater levels in the Mississippi Delta have declined more than 6.4 m since 1970 due to extraction to irrigate agricultural crops. Although more on-farm water storage ponds have been constructed in recent years to mitigate groundwater depletion in Mississippi, little effort has been devoted to addressing the question of how many hectares of crop land can be irrigated with water from one hectare of agricultural pond. We developed a computer modeling tool to meet this need.

Summary

Groundwater levels in the Mississippi Delta have declined more than 6.4 m since 1970 due to extraction to irrigate agricultural crops. With increasing concern over groundwater depletion, more on-farm water storage ponds have been constructed in recent years in Mississippi. However, the optimal ratio of pond size to irrigated crop land area was not known. That is, how many hectares of crop land can be irrigated with one-hectare of pond water? Knowing this ratio is crucial to cost-effectively constructing the proper size pond, managing pond water for crop irrigation, and mitigating groundwater depletion in Mississippi and in other regions of the U.S. with similar needs.

Diagram showing the pond hydrological processes

A schematic diagram showing (a) the pond hydrological processes and water budget used in model development, and (b) a photo of a pond in Macon, Mississippi used for model application.

Scientists from USDA-FS and USDA-ARS developed a modeling tool to address this issue using the STELLA (Structural Thinking, Experiential Learning Laboratory with Animation) software. A schematic diagram showing the pond hydrological processes and water budget that have been incorporated into the model is shown in the accompanying figure. The model was applied to determine the ratio of pond size to irrigated soybean land for a typical pond that represented the average conditions in east Mississippi and the Mississippi Delta. One of our simulations shows that a reasonable ratio of pond size to irrigated soybean land is 1:18 if the scheduled irrigation rate is 2.54 cm/d, the average pond depth is 1.83 m, and the pond water level is drawn down to 0.38 m. A maximum ratio of pond size to irrigated soybean land could be 1:20 if the pond water level is drawn to near zero. Using the ratio of 1:18, a one-ha soybean field could save about 542 m3 of groundwater each year. Results suggest that an on-farm water storage pond is one of the promising alternatives to conserve groundwater resources. The resulting model and findings from this project could have substantial impacts on 1.82 million hectares of crop land in Mississippi. Other regions of the United States with similar interests of conserving groundwater resources would also benefit from using this predictive tool.

Principal Investigator
Ying Ouyang, Research Hydrologist
RWU
4155 - Center for Bottomland Hardwoods Research
Strategic Program Area
Water, Air, and Soil
Publications
Estimating the ratio of pond size to irrigated soybean land in Mississippi: a case study
A model to estimate hydrological processes and water budget in an irrigation farm pond
CompassLive Story
Farm Ponds Conserve Groundwater in MS
Research Partner
Theodor D. Leininger, Project Leader/Research Plant Pathologist
External Partners
Gary Feng, John Read, and Johnie Jenkins, USDA-ARS, Starkville, Mississippi
Joel Paz, Department of Agricultural and Biological Engineering, Mississippi State University