WATER LAW IMPACTS ON HYDROLOGIC FUNCTION

To maintain water quality and quantity, we need to understand the interactions between human activity and the water cycle. Since human activity is mediated by the law, water rights law is a logical starting point in characterizing the mechanisms by which humans affect water. In the United States, water rights law is addressed at the state level. In the eastern states, owners of the land adjacent to a water body share equal use rights to the water. This is referred to as the Riparian Doctrine. In the Prior Appropriation (P.A.) system favored by some western states, water rights are established independent of land ownership. To obtain a water right, a party must detain or divert water from its natural course and make “beneficial use” of it. Most P.A. beneficial uses are highly consumptive activities in terms of both quality and quantity.

Using a paired basin approach, we examine catchment response to legal dynamics across geographic and size gradients. Utilization of historic data including USGS gauging data and NCDC climate data along this divide can provide basin pairs with extended historical data. Preliminary data from a basin pair (L. Nemaha River, NE/Tarkio River, MO) shows that the P.A. basin displays a consistently lower runoff: rainfall ratio than the Riparian basin. In fact, the P.A. runoff: rainfall ratios are on average 60% of those in the Riparian member (r² = 0.67), despite a spatial proximity of ~45km, strongly suggesting that P.A. law diminishes yield. New well registrations for the basins cannot explain the difference: Both basins show a sharp increase in new wells post-1990, with few records pre-1950. Interestingly, NID data shows that cumulative Nemaha dam registrations are roughly equal to Tarkio’s in 1950, but outnumber Tarkio dams on average by a factor of 6.5 between 1950 and present, and by as much as a factor of 14 in 1965.