Amount of Recharge Through Playas
Playa experts agree that playas recharge the aquifer at the rates described in the 2009 USGS Circular: Recharge Rates and Chemistry Beneath Playas Literature Review, which gathered and reviewed all the scientific literature about recharge to the High Plains Aquifer. According to the report authors, “Reported recharge rates beneath playa floors range from about 0.01 to more than 10 in./yr, whereas most interplaya settings in croplands and rangelands have recharge rates reported to range from about 0.01 to 1 in./yr.” The scientists at the Summit supported using an average of 3 inches per year across the region in calculating recharge rates through playas.
As the USGS recharge report indicates, recharge rates vary based on a number of factors including depth to aquifer, soil type, amount of soil saturation, evaporation and transpiration, and amount of rainfall. Recharge rates also vary during the playa wet/dry cycle. According to the USGS report, most recharge occurs through the large cracks that form in the dry, clay soils in the bottom of the playa. During a rainstorm, water runs off the landscape and into the cracks, eventually making its way to the aquifer. Then when soils become saturated and the cracks close, water continues to seep into the soil and slowly moves downward along roots and small channels, as well as along the playa’s perimeter where the clay soils meet the upland soils. Recharge during this time happens at a much lower rate.
The USGS recharge report concludes that “properly functioning playa wetlands … are thus important for the overall recharge contribution to the southern High Plains aquifer.”
Time to Recharge Through Playas
In general, water recharging today through playas will be available for our children and/or grandchildren. The time it takes for recharge to reach the aquifer and be available for extraction varies depending on depth to the aquifer formation and underlying soil type. If it is shallow, water will recharge in months to years. If the depth is approximately 100 feet, it will take years to decades. If the depth is approximately 200 feet, water will recharge in decades. At the deepest locations, recharge could take a century to reach the aquifer.
Quality of Recharge Through Playas
The benefit of a healthy playa — a playa with a grass buffer and no hydrological modifications such as pits or ditches — goes beyond simple recharge. Research shows that water reaching the aquifer through playas is of higher quality than that going through other pathways. This happens in two ways: first, as rainfall and runoff travel toward the playa, the surrounding grasses trap sediments, which can carry contaminants into the playa; then, as the water moves through the clay floor of the playa, a second ‘cleaning’ process occurs as the soils beneath the playa remove nitrates and other dissolved contaminants. The result is high quality water reaching the aquifer that can then be used by those living on the land.
Direct Recharge Benefits to Landowners
Once the water reaches the aquifer, it is yours to use. Unlike a lake, the aquifer is made up of many smaller sections with extremely slow water flow between sections (1⁄2-1 mile per 10 years). Thus, the water is functionally compartmentalized in a given area. That means the water recharging through your playa benefits you directly and provides high quality water that can be used by you, your children, and future generations.
