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Delta Irrigation Water Management
The Mississippi Delta of Missouri encompasses about 4,000 square miles, or 2.5 million acres, of prime agricultural land. This region was originally covered by forests and swamps but has become intensively developed for agricultural production. The Mississippi River Valley alluvial aquifer is the surficial unit in the area, except where older units crop out on Crowley's Ridge. The thickness of the alluvial aquifer ranges from 0 to more than 250 feet, but generally is 100 to 200 feet thick. Water levels fluctuate seasonally, but water levels seasonally return to previous levels during recharge from precipitation that averages 44 to 50 inches per year. The aquifer is characterized by large transmissivities that can exceed 50,000 feet squared per day. Water wells easily can yield 1,500 gallons per minute and can exceed 3,500 gallons per minute. The aquifer is a significant source of water for domestic, irrigation, and public-supply use that annually provides an estimated 500,000 acre-feet of water for irrigation and 17,000 acre-feet of water for municipal, industry, and domestic use.
The excessive transmissivities of the Mississippi Delta alluvial aquifer and the rapid leaching characteristics of a major portion of soils in the project can result in contamination of areas well removed from the project area itself, e.g. the Big Lake Wildlife Refuge located just across the Missouri state line in Arkansas.
The large quantities and volumes of pesticides and nutrients being applied to crops above the shallow and fragile alluvial aquifer will continue to add to the present contamination levels of the aquifer.
The management complexities of intensively irrigated lands in the project emphasize the need for comprehensive nutrient-pesticide management plans and maximum efficiency water delivery systems to be adopted by producers in the region.
PROJECT DESCRIPTION
The project area encompasses the major land resource area referred to as the Mississippi Delta. This area encompasses about 2.5 million acres for prime agricultural lands.
Project demonstration activities will be targeted within the 700,000 acres of irrigated cropland consisting of, corn - 300,000 acres; soybeans - 200,000 acres; rice - 100,000 acres; and cotton - 100,000 acres that are a part of the Little River Drainage District. Essentially all these acres drain into the Big Lake Wildlife Refuge.
Overview:--Flood irrigation systems currently used in Missouri require irrigation water to be pumped into the highest basin in the system. After this basin is filled, water cascades into the next lower basin and so on until all basins are full. It is difficult to manage this type of system without inducing runoff. Because each basin must be completely filled before the lower basins can receive water, rain falling on the field runs off.
Three irrigation management demonstration systems, up to seven sites, are proposed to meet project goals of preserving or enhancing the surface and groundwater and environmental resources of the project region.
A description of the above three systems follows:
1. SIDE INLET FLOOD: A side inlet system allows water to be applied to each basin independent of water levels in other basins. Water is delivered to each basin through a pipeline or an irrigation canal. The system can be set so that all basins fill at the same time.
Project Goals: Demonstrate the side inlet flood irrigation system and the benefits of using such a system. There are no known side inlet flood irrigation systems used in Missouri.
Targeted Areas: There are approximately 100,000 flood irrigated acres in Missouri. The number of acres of rice, and thus flood irrigation systems, grow each year. Use of side inlet flood irrigation systems will reduce irrigation runoff into the St. Francis, Black, and Little Black Rivers, Cane Creek, and the Little River Drainage District system which flows into the Big Lake Wildlife Refuge in Arkansas. Reduced pumping will conserve water in the Mississippi alluvium aquifer.
Benefits: The advantages of the side inlet irrigation system are 1) A flood depth can be maintained which will allow for the additional storage of a 1 to 2 inch rainfall; 2) Because each basin can be filled individually or at the same time, it is easier to maintain the irrigation flood without inducing runoff; 3) A shallow flood can be maintained, which increases rice yields; 4) Harvesting more rain water reduces the volume of required cold ground water, thus reducing rice yield losses due to cold water temperatures; 5) Less pumping reduces operating costs and conserves energy; 6) Ground water is conserved; and 7) Reduced runoff minimizes negative off-site effects.
Crops other than rice are damaged when flood irrigated with the cascade flood irrigation method. This is due to the prolonged exposure to water in the upper basins. Upper basins are flooded while water is moving down to lower basins. A side inlet system will allow for efficient flood irrigation of crops other than rice.
Without the side inlet type system, the cascade flood irrigation system will continue to be used, requiring more ground water use and more tail water runoff from contour flood irrigation systems.
Site Description: Three sites are proposed. Two sites will have an underground pipeline to deliver water to each flood basin. The third site will use layflat tubing. A valve will be adjusted so that equal flow enters each irrigation basin. Instruments will be set to measure the volume of water added through pumping and rainfall and the volume of water lost to tail water. Samples will be taken of runoff (if it occurs) to determine the quantity of nutrients leaving the field. This can be used to measure the benefits of reduced runoff.
2. SURGE IRRIGATION: Surge irrigation is used to improve the uniformity of water entering the soil down a row in a furrow irrigation system. Water is introduced to one area of the irrigated field for a certain duration, then switched to a different irrigated area, then returned to the original area. Switching back and forth is continued until the entire length of the furrow is watered. By pulsing, or surging, the water advances down the furrow faster than it would have with a constant flow in the conventional furrow irrigation system. By decreasing the time to advance to the end of the furrow, deep percolation is reduced. This is particularly true in courser textured soils. Surge valves are required to automatically switch irrigation water.
Targeted Area: Approximately 100,000 acres of loamy to sandy textured furrow irrigated soils.
Benefits: Reduced deep percolation of irrigation water which can potentially degrade ground water with leached nutrients and chemicals, energy conservation, and increased yields.
Site Description: Two demonstration sites will compare deep percolation quantities to those from conventional furrow irrigation systems. Opportunity timers and flumes will measure soil intake characteristics to determine best surge management schemes.
3. FURROW FLOW IMPROVEMENT: Use of recently developed technology can enable furrow irrigation systems using layflat irrigation tubing to apply water uniformly to individual furrows as needed. A computer program calculates the needed gradient of the crown end of a field to match energy losses within the pipeline to equalize furrow flow streams. The program selects hole sizes to help make existing systems operate more efficiently. Uniform furrow flow streams result in water conservation (from 1 to 10 in/acre per year), reduced potential of surface water contamination through reduced irrigation tail water (from 1 to 6 in/acre per year) and increased yields. Approximately 200,000 acres could be furrow irrigated each year using the layflat irrigation tubing system.
Site Description: A total of two demonstration sites are proposed. System improvements will be demonstrated through use of multiple hole sizes and through proper grading of the crown portion of the field.
Field measured evaluations will determine the volume of water pumped versus water lost to deep percolation and tail water. Demonstrations of "before" and "after" improvements will be presented.
Water and soil samples will be gathered prior to and following irrigations to quantify the movement of nitrogen below the root zone and off the field.
Benefits: To assist irrigators in applying furrow irrigation water more uniformly, a computer program has been developed which uses the elevations of the crown end of the field and computed friction loss to find the pressure at each watered furrow. The computed pressures are used to either size holes for existing crowns or to design crown gradients so that one hole size can be used. The program uses proportionately varying flow rates for odd shaped fields. The program evaluates the adequacy of existing systems to demonstrate the benefits of improvements, including:
a. Demonstrate the benefits of grading the crown end of furrow irrigated fields to properly distribute furrow irrigation water.
b. Demonstrate the benefits of using varying hole sizes to properly distribute furrow irrigation water.
c. Reduce irrigation water pumped, tail water, and deep percolation to minimize negative off site impacts.
PRODUCTS
The project status will be kept up-to-date with the required quarterly reports submitted to DNR. Site specific reports will be generated on an as-needed schedule. This will include evaluation of water quality sample data and the impact of project measures. Results, attendance, etc. from workshops, tours, and public meetings will be released in newsletters and other media forms.
The project calls for demonstrations of three irrigation systems at 7 possible site locations. A total of 1 workshop, 3 tours and 2 public meetings are anticipated over the project period. A comprehensive information/education program will provide pamphlets, brochures, and guide sheets relating to project demonstration activities.
PROJECT SPONSOR
Bootheel RCandD
COOPERATING AGENCIES/PARTIES
USDA-NRCS, MO Rice Council, farmers, University Extension Service
CONTACT:
Bootheel RCandD
#7 East Market
Dexter, Mo. 63841
Mike Mick 573-624-7403
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