(Connie Jo Discoe/McCook Daily Gazette)
A similar study of the coordination of surface and groundwater was done on the Platte River (February 2006), Don Felker, general manager of Frenchman Valley, said. This "Republican River Basin Conjunctive Water Management Study" is the first on the Republican, he said.
According to the Nebraska Department of Natural Resources (DNR), "The concept of 'conjunctive management' is that surface and groundwater resources are hydrologically interconnected, and decisions to improve the management of one cannot be made properly without considering the other. Hence, management should consider surface and groundwater as components of one resource."
Water ran this fall in the canal northwest of Culbertson as part of the Republican River Basin conjunctive water management study that started April 12, 2012, and expires in February 2013.
Addressing questions associated with the water in the canal this time of year (after irrigation season), Felker said that the canal is not draining Enders Lake, nor is its sole purpose to pass through the Republican River Basin in Nebraska to Kansas.
The Republican River Basin program will examine the benefit of groundwater recharge from canals, and also study the affect of climate, such as drought, on both surface and groundwater supplies.
Information provided by Felker and the FVID, the DNR and Natural Resources Districts indicates that, "An open, unlined canal that is filled with excess streamflow will seep water into the aquifer, and the water will gradually find its way back to the stream through time."
According to "Increasing Future Water Supply via Augmented Groundwater Recharge," "The concept that an unlined canal provides water to an aquifer is well understood in Nebraska's irrigation districts which have been passively augmenting aquifers for more than 100 years during their normal water delivery operations."
The study explains, "The rate at which water returns to the river depends upon how much connected pore space and effective thickness the aquifer has (transmissivity) and the distance of the canal from the stream." Seepage continues to influence river flows over a period of years or decades.
The Platte River study examined whether curtailing surface water harmed groundwater supplies and whether recharge also benefitted surface flows because groundwater baseflow is an important source of river water, especially in dry periods.
According to the Platte River study, the concept of conjunctive water management involves either a physical or a paper exchange of surface and groundwater.
The study stated, in early 2006, that:
* A physical exchange of water involves the recharge of surface water into the groundwater and the resulting increase in subsurface stored water. The storage volume added underground is then available to be pumped during a dry season or prolonged drought period.
* A paper exchange of water involves the substitution of one type of water supply for another. (For example, surplus surface water may be supplied to an irrigator who then foregoes the use of groundwater, leaving the groundwater underground for future use.) The net effect on the aquifer is more water in storage.
The study found that:
* Surface water use usually has a benefit to the groundwater through recharge, (which can replenish an aquifer and, in some case, improve quality) or cause contamination.
* Groundwater use usually has a beneficial impact on the surface water through baseflow (which sustains flows in droughts) or an adverse effect through streamflow depletion.
The case study states that it is because of these linkages that the concept arises of managing surface and groundwater resources "in a coordinated or conjunctive manner."