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Using MARORA to to Assess Economic and Environmental Impacts of On-Farm Reservoirs : 

Using MARORA to to Assess Economic and Environmental Impacts of On-Farm Reservoirs J. Popp, K. Young, E. Wailes, & J. Smartt Department of Agricultural Economics and Agribusiness University of Arkansas

Introduction: 

Introduction Nearly 4 million of a total 7.7 million acres of harvested cropland are irrigated in Arkansas. Dominant crops: rice, cotton, & soybeans. The annual farm value is nearly $1.5 billion plus $2.5 billion in further processing (USDA,NASS,2000).

Introduction: 

Introduction Rice, soybean and cotton production rely heavily on well water pumped from the alluvial aquifer. Extensive pumping is resulting in the steady depletion of this aquifer. At this rate, aquifer-dependent rice and soybean in much of eastern Arkansas will not be sustainable for more than 20 years.

Introduction: 

Introduction Farmers are turning to on-farm reservoirs and tail water recovery systems to assist in meeting their water requirements. These reservoirs/recovery systems may produce an added benefit – reducing the amount of sediment that leaves a field.

Purpose : 

Purpose Evaluate the use of on-farm reservoirs/ tail water recovery systems in conjunction with other BMPs with regard to : economics water use sediment loadings Evaluations conducted with the MARORA model

Presentation Outline : 

Presentation Outline Groundwater situation MARORA model Evaluation of management practices Results Conclusions

Groundwater Situation: 

Groundwater Situation Nearly half the state under current, future or proposed critical ground water area designations

Groundwater Situation: 

Groundwater Situation Diversion of additional surface water potential for ecosystem damage potential for exacerbated sedimentation problems (focus of TMDL in Arkansas). TMDL requirements: L’Angille River – reduce non-point source sediment loadings by roughly 40% during critical periods

On-farm Reservoir: 

On-farm Reservoir Can reduce depen-dence on ground & other surface water sources

Tail Water Recovery: 

Tail Water Recovery Designed to capture most farm runoff and reduce sedimen-tation of surface waters

MARORA Model: 

MARORA Model Modified Arkansas Off-stream Reservoir Analysis Uses weather, farm, field, and economic data related to rice and soybean production to simulate income and expenses associated with on-farm reservoirs. optimization mode: identifies reservoir size that will maximize NPV income over 30 years. non-optimization mode: calculates costs and returns for a specified reservoir size

Analysis : 

Analysis Evaluation of reservoirs and BMPs with respect to economics water use sedimentation losses Best Management Practices (BMPs) shorter season rice irrigation efficiency - underground pipe only irrigation efficiency - underground pipe & laser leveling

Model Assumptions: 

Model Assumptions Baseline model assumptions: 320 acre field; reservoirs result in the reduction of cropland area by the area occupied by the reservoir specified reservoir filled once in spring from surface water and field runoff; tail water returned throughout the system crop rotation: 2/3 soybean, 1/2 rice silty loam soil discount rate 8% crop prices adjusted to reflect price plus gov’t pmts production costs from the 2001 CES budgets laser leveling $300/ac

Model Assumptions: 

Model Assumptions Baseline model assumptions (con’t) excavation costs for reser construction $1.00/cu yd underground pipe cost $50.00/ac soybean yield 50 bu/ac and rice yield 160 bu/ac laser leveling can increase yields by 8.5% in BMP scenarios irrigation efficiency: 50% rice; 45 % soybean water recovery efficiency: 80% (based on relift pump and temporary on field storage availability) good ground water: 50 ft sat thick, 0.5 ft annual decline poor ground water: 30 ft sat thick, 1.0 ft annual decline projection period: 30 years

Baseline Analysis - “Good” Ground Water Situation: 

Baseline Analysis - “Good” Ground Water Situation Good ground water supply situation: 50 ft saturated thickness 0.5 ft annual decline 320 acre field Reservoir not profitable over 30 year period Sensitivity analysis shows profitability of reservoirs starts at roughly 35 ft sat thick Average annual sediment loss: 38.12 tons

Baseline Analysis - “Poor” Ground Water Situation: 

Baseline Analysis - “Poor” Ground Water Situation Poor ground water supply situation: 30 ft saturated thickness 1.0 ft annual decline 320 acre field 620 ac ft reservoir (251 ac left in production) Average yearly income $40,485 Irrigation water: rice 42.6” soybean 24.8” Soil: lost 7.12 tons, recovered: 28.48 tons

Short Season Irrigation: 

Short Season Irrigation

Increased Efficiencies – Underground Pipe and Laser Leveling: 

Increased Efficiencies – Underground Pipe and Laser Leveling

Summary and Conclusions: 

Summary and Conclusions On-farm reservoirs/tail water recovery systems have the potential to capture much of the sediment that would have left the farm Sedimentation recovery is tied to efficiency of tailwater recovery system Tail water pit and pump: 5-25% Tail water pit, pump and temp in-field storage: 10-40% Reservoir, tail water pit and pump: 10-50% Reservoir, tail water pit, pump and temp in-field storage: up to 90%

Summary and Conclusions: 

Summary and Conclusions Under good ground water supply conditions, sedimentation reductions do not pose a sufficient benefit to support construction of reservoir Regulatory environment could change that in the future Cost sharing opportunities might reflect benefit of reduced sedimentation to surface waters

Summary and Conclusions: 

Summary and Conclusions Under poor ground water supply conditions, BMPS such as reservoirs, laser leveling and underground pipes can enhance profits reduce ground water dependency reduce surface water sedimentation Management practices such as shorter irrigation seasons that may increase profitability and reduce water usage, may actually increase sedimentation loss

On-going Research: 

On-going Research Incorporate salt and water balance model in order to blend surface and ground waters to reduce potential for crop (rice) damage due to salinization

Slide30: 

Questions?