Modeling Accretions to Baseflow in Response to a Scenario of High-Flow Diversions into Canals

Tuesday, September 22, 2015: 11:10 a.m.
Colby Osborn , Natural Resources, State of Nebraska, Lincoln, NE

Snowmelt in the early spring and heavy thunderstorms can create high streamflow events and pose flooding threats to areas along streams in the Central Platte River Basin in Nebraska. For floodwater relief and the retiming of water for later use, the State of Nebraska implemented a proactive management approach in partnership with local natural resources districts and irrigation districts, diverting the high flow into canals that extend into agricultural fields and allowing the diverted flows to recharge the aquifer. To make optimal integrated water management decisions, it is essential to estimate the amount and timing of changes to stream baseflow. Work already completed by the Nebraska Department of Natural Resources used analytical tools to evaluate the impacts of diverted flows. Numerical modeling is an additional tool available that complements analytical tools.

This numerical analysis uses COHYST, a regional groundwater model, to gain a better understanding of the relationship between the diversion of water into canals along the Platte River and the resulting impacts to streamflow. Thirteen canals within the Central Platte River Basin received an arbitrary diversion of 100,000 cubic feet per day for the first simulation month. After using data from the model runs, the accretion to baseflow from individual canals was calculated. After the 21 years modeled, the percentage of the diversions that returned to the stream ranged from approximately 30 percent to nearly all of the total diverted water, and the timing of the peak return ranged from shortly after the diversion to a couple of years afterwards. These variations were most consistently dependent on the canals’ proximity to the stream. Fluctuations and anomalous spikes found within the baseflow response curves were concluded to be a result of numeric noise. This presentation will describe the analysis and results.

Colby Osborn, Natural Resources, State of Nebraska, Lincoln, NE
Colby Osborn received a B.S. in geology from the University of Nebraska-Lincoln in 2014. He was hired by the Nebraska Department of Natural Resources in 2014 as a Specialist in the Integrated Water Management division. His major duties include: conducting specialized and complex hydraulic and hydrologic analyses on relationships between groundwater/surface water, and developing scientific and technical data and analyses for the integrated surface water/groundwater management planning process.