Location: Northwest Irrigation and Soils Research
Project Number: 2054-13000-009-04-I
Project Type: Interagency Reimbursable Agreement
Start Date: Jul 31, 2017
End Date: Sep 30, 2019
Evaluate the effects of conservation practices in the Upper Snake Rock watershed.
We will continue collecting water samples weekly during the irrigation season and biweekly during the winter from 10 sites (8 return flow and 2 inflow sites) in the Twin Falls irrigation tract to calculate sediment and nutrient balances for the watershed. We will cooperate with Idaho Department of Water Resources (IDWR) to continue measuring return flow at eight sites that we have cooperatively maintained since 2005. Return flow data from all sites will be used to calculate annual water balances for the watershed. Water balances will be used to determine if the amount of return flow relative to the amount of irrigation water diverted has decreased as more land has converted from furrow to sprinkler irrigation. Sediment and nutrient losses will continue to be measured at three sites within a 200 ha subwatershed. A fourth site will be added to measure additional flow into the subwatershed that initiated when a new center pivot was installed outside of the subwatershed. These sites isolate the water contributed from sprinkler and furrow irrigated fields within this subwatershed. Total irrigation water diverted on to the Kimberly ARS North Farm and total runoff from the farm will be measured in 2018 in addition to total runoff from two furrow irrigated fields (15 ha) on the farm. These data will be used to quantify field-scale water use efficiency and sediment and nutrient losses. Irrigation methods within the Twin Falls irrigation tract have been estimated by biennial field surveys of one randomly chosen square mile section (260 ha) within each of the 17 townships in the watershed. Total area surveyed with this method is 4,400 ha or about 5% of the total land area in the watershed. The feasibility of using aerial photography to determine irrigation type on every field in the watershed, or a larger portion of the watershed, will be explored in 2018.