The importance of flood irrigation in water supply to wetlands in the Laramie Basin, Wyoming, USA

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Year Published: 2001
Month Published: SEP
Author: Peck, DE and Lovvorn, JR
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As in many areas of western North America, flood irrigation for hay production has created many wetlands in the Laramie Basin, Wyoming. Since the early 1900s, water from mountain snowmelt has reached wetlands via ditches and as interflow and ground water percolating from flooded fields and unlined ditches. Such systems are viewed as inefficient for irrigation and other human uses because they reduce the volume and increase the salinity of downstream flows. Increasing irrigation efficiency by lining ditches or installing sprinklers would decrease wetland habitat, but such effects are seldom considered. To assess potential impacts of increased irrigation efficiency, we determined how flood irrigation affects the hydrology and types of wetlands in the Laramie Basin. For 74 wetlands with 80 total inflows, just 14% of inflows were as surface flow from natural stream channels. In contrast, 65% of inflows were directly from irrigation: 30% as surface flow from ditches and 35% as interflow percolating from ditches and irrigated fields. Fifteen percent of inflows were as surface flow from other wetlands, and 6% of inflows were from ground water with unknown recharge source (probably either natural streams or irrigation). In this year of high water availability (1999), wetlands receiving surface water generally were fresh or oligosaline regardless of whether that flow was from natural streams, other wetlands, or ditches (mean +/- 1 SD = 3.28 +/- 5.07 mS/cm, median = 1.60, range 0.07-22.10). In contrast, wetlands receiving water as interflow percolating from ditches or irrigated fields, or as ground water with unknown recharge source, were more likely to have conductivities of mesosaline or higher (mean +/- 1 SD = 22.45 +/- 32.71 mS/cm, median = 9.08, range 0.60-112.00). Conductivity of surface water in the 74 wetlands (mS/cm) ranged from fresh (0.07) to hypersaline (112.00), with a mean of 10.89 +/- 22.80 (SD) and median of 2.60; this range of salinity corresponds to substantial variation in wetland community structure. In the Laramie Basin and similar areas, flood irrigation is critical to the existence, hydrology, and community types of most wetlands, and these effects should be considered in plans to increase irrigation efficiency.

Pages: 370-378
Volume: 21
Number: 3
Journal ISO: Wetlands
ISSN: 0277-5212
DOI: 10.1672/0277-5212(2001)021[0370:TIOFII]2.0.CO;2

flood irrigation; irrigation efficiency; Laramie Basin; Rocky Mountain wetlands; saline wetlands; wetland hydrology

Source: Web of Science
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