On-Farm Water Storage Systems and Surface Water for Irrigation

MISSISSIPPI STATE, MISSISSIPPI

   What Is an OFWS System?

   An on-farm water storage (OFWS) system is a structural best management practice that captures and stores surface water runoff so that it can be used at a later time for irrigation. These systems can capture runoff both from rainfall and tailwater from furrow irrigation, and they can be constructed with only a storage pond, with an enlarged tailwater recovery (TWR) ditch, or with a TWR ditch and a storage pond (Figure 1). The pond is typically constructed on an area of the farm that is less productive, such as a low-lying area that does not drain well. The TWR ditch and pond are positioned where they can capture adequate runoff yet remain accessible to fields that will be irrigated using the stored water. The designs of the systems vary depending on where in Mississippi they are installed. It is important to note that Section 404 of the Clean Water Act (CWA) requires a permit for the discharge of dredged or fill material into waters of the United States, which includes wetlands.

   History of OFWS Systems

   In Mississippi, irrigation first began in the Delta area in the 1970s and has steadily increased. This increase in irrigation is mostly a result of easy access to the shallow groundwater in the Mississippi River Valley (MRV) alluvial aquifer, low energy costs, and the availability of pumps and power plants. Unlike in the western United States, where the federal government helped implement major infrastructure projects such as dams and reservoirs to support irrigation, the expansion of irrigation in the southeastern United States has been primarily due to private investment by farm owners. No large federal projects have been implemented to date.

   In 1982, Mississippi had 430,901 irrigated acres. In 1992, that number had more than doubled to 882,976 irrigated acres, moving Mississippi into 19th in the country for states with the greatest number of irrigated acres. In 2012, Mississippi moved to ninth in the country with 1,651,978 irrigated acres (NASS, 2004; NASS, 2014). Conversely, the number of irrigated acres in most western states has decreased. This is due to the increasing demands for water resources from growing urban populations and over-allocation of water resources.

   Increased dependence on irrigation has become an issue. Current irrigation systems are expected to reduce risk, withstand periodic droughts, and maintain or increase profits. However, these expectations have caused the groundwater in the MRV alluvial aquifer to be pumped at a faster rate than it is being refilled, resulting in declining aquifer levels in the Delta over the past three decades.

   The Mississippi Department of Environmental Quality (MDEQ) is responsible for managing all of the state’s waters and has recognized and responded to this growing concern. In November 2011, the executive director of MDEQ established the Delta Sustainable Water Resources Task Force, which is led by MDEQ’s executive director and includes representatives from Delta Council, Delta Farmers Advocating Resource Management (Delta F.A.R.M.), Mississippi Farm Bureau, the Mississippi Soil and Water Conservation Commission, the Natural Resources Conservation Service (NRCS) of the U.S. Department of Agriculture, the Vicksburg District of the U.S. Army Corps of Engineers, and the Yazoo-Mississippi Delta Joint Water Management District. The task force was formalized by Executive Order No. 1341, signed by the governor of Mississippi on August 26, 2014. The task force aims to manage water as efficiently as possible, store water when it is plentiful to use at times when it is not, and pursue all feasible alternative water supplies.

   While concerns over aquifer declines and the availability of water for irrigation were escalating, there was also growing concern about the issue of hypoxia (oxygen deficiency) in the Gulf of Mexico. The Mississippi River Basin contains approximately 65 percent of the United States’ harvested cropland, and the Mississippi and Atchafalaya Rivers contribute over 85 percent of the total nutrient load to the Gulf (Dunn, 1996; Kolpin, 2000). Excess nutrient runoff increases aquatic primary production, which is often indicated by algal blooms (Dubravko et al., 2005). When this plant material dies and is degraded by bacteria, oxygen is consumed, depleting oxygen levels in the water column. Hypoxic conditions occur when oxygen levels in the water reach 2 milligrams per liter or less. The northern Gulf of Mexico contains one of the largest hypoxic “dead” zones in the world (Renaud, 1986; Rabalais et al., 2002).

   The Mississippi River Gulf of Mexico Watershed Nutrient Task Force, formed in 1997, set a goal to reduce the size of the Gulf hypoxic zone to less than 5,000 square kilometers by the year 2015. The average size of the Gulf hypoxic zone in 2005–2010 was 17,300 square kilometers, and the size in 2010 covered 20,000 square kilometers (Rabalais and Turner, 2010). The size of the hypoxic area fluctuates from year to year, depending on the amount and timing of spring and summer rainfall, the associated discharge from the Mississippi River, and wind speed and wind direction, among other factors. The most recent mapping of the Gulf in July 2017 recorded a hypoxic area of 22,720 square kilometers, the largest size measured to date since mapping began in 1985 (LUMCON, 2017).

   In 2009, the USDA-NRCS launched the Mississippi River Basin Healthy Watersheds Initiative (MRBI). This initiative provided additional funds to support voluntary conservation practices in selected focus area watersheds in participating states to reduce nutrient loading and improve water quality in the Basin and Gulf of Mexico. When the MRBI program first began, there were 12 participating states, including Arkansas, Illinois, Indiana, Iowa, Kentucky, Louisiana, Minnesota, Mississippi, Missouri, Ohio, Tennessee, and Wisconsin.

   When the MRBI was first implemented, there were three focus area watersheds in Mississippi: Big Sunflower (08030207), Upper Yazoo (08030206), and Deer-Steele (08030209) (Figure 2). In 2011, the Coldwater Creek Watershed (08030204) in northwest Mississippi was added. South Dakota began participating in 2012.  ∆