Helping You Conserve Natural Resources For 35 Years...

Upper Republican Natural Resources District

Groundwater Management

Allocations

The NRD looks at two groundwater issues in calculating the Allocation.
These are:

· Recharge. The downward movement of water through the soil to groundwater.

· Withdrawal. Water pumped from groundwater for use.

The State has given districts a variety of regulatory tools to deal with contamination, shortages, or user conflicts. The URNRD has a formal plan to protect ground water.

The URNRD's long term goal is to extend groundwater reservoir life to the greatest extent practicable consistent with beneficial use of the groundwater & best management practices, and to protect the quality of the aquifers within the District boundaries.

Simply put, when the withdrawal rate is larger than the recharge rate over a period of time, the level of the top of the groundwater declines. The rate of decline is determined by the the difference in the Withdrawal and Recharge rates over time.

The NRD is manages each township to have a decline of less than one quarter of one percent per year in the saturated thickness (the distance from the top to the bottom of the groundwater) in a year.

Allocations are set for a 5 year period. In establishing the Allocation amount the NRD also considers:

· Historic and recent patterns and volumes of groundwater recharge and irrigation water use have been and resulting changes in the level of the groundwater.

· Changes in irrigation methods and efficiencies.

· Crop rotations being used through out the district.

· Importance of the groundwater to the economic well being and stability of the District.

· Need to extend the useful life of the groundwater to all citizens, current and future

 

Regulation of Irrigation Wells

The NRD has to consider a number of factors when considering to establish or end a moratorium. Among the most critical to study in establishing a moratorium are:

· Drawdown. The decline of water below the static water level when pumping; (water table) The lowering of the elevation of the groundwater table from the pumping of wells or drought.

· Capture Zone. The zone around a well contributing water to the well; the area on the ground surface from which a well captures water.

Drawdown of the water table and the capture zones of individual wells are critical as they determine the relationship between wells. If the water level is lowered too much, then shallower wells may go dry as the water level goes below the well screen. As wells are pumped they draw water from a specific area that is determined by:

· Qualities of the rock, gravel or sand the water is found in.

· Steepness of the gradient.

· Rate and frequency that water is being pumped.

 

As the number of wells increases and more water is pumped the water level goes down and the drawdown increases. How fast the drawdown increases and how permanent it is depends on:

· Amount of recharge.

· If water is being pumped upgradient.

· Rate and frequency of pumpage.

 

The capture zone is defined by the length and width of the area that it draws water from.

· When wells are spaced out evenly and their pumping rates are managed within the normal allocation, the capture zones remain far enough apart that water moves past them to reach down gradient wells. The operation of each well would not normally interfere with the seasonal operation of other wells.

· When wells are spaced to close, even if the pumping rates are in line with the allocation, the normal capture zones will overlap and the over drawing of water may occur. In this event, the pumps have to work harder and the volume of water reaching some wells may not be adequate to meet irrigation needs.

· Even if wells are spaced evenly, if one well pumps an extreme amount, the capture zone may reach out and capture or affect the water that would normally reach other wells. If several wells in a localized area are doing this, the drawdown will be excessive.

The moratorium was put into place to help manage the problems associated with overlapping capture zones resulting in areas where a number of wells are close to each other. It also helps to slow the drawdown of the water level for approximately 3,300 irrigation wells. At the time these wells were drilled, there was only limited knowledge of how much interaction can occur between the capture zones to impact neighboring wells and associated irrigation.

The numerical difference between the original  and current water levels equals the drawdown. NOTE: The drawdown also extends sideways to the direction of the gradient and in proportion to the rate and volume at which water is being pumped.