John Moorhouse, RAC Chairman
At the August meeting held in Forsyth, the Yellowstone River Conservation District Council issued a Position Statement for modernizing age old irrigation ditches. Chairman of the Resource Advisory Committee John Moorhouse said “Most irrigation ditches in Montana can lose up to 50% of the water they diverted from their source.”
The YRCDC is chaired by Don Youngbauer, Forsyth, and is made up of the 11 Conservation Districts along the Yellowstone River. For over 10 years the YRCDC has been studying the river and its cumulative affects on its surrounds.
RAC Chair John Moorhouse said seepage from ditches is not only wasteful of our precious water, but it also affects the stability of the ditch structure itself and can cause ditchbank failure that can result in flooding and extensive repairs.
“The perfect solution,” Moorhouse continued, “is an irrigation pipeline, either buried or on the surface. This prevents water loss from leakage and evaporation as well. The cost for this cure is often too prohibitive. Therefore lining ditches with impervious material that prevents or greatly reduces water loss is recommended as a less expensive alternative,” Moorhouse concluded.
The Position Statement issued by the Council is shown below:
Adopted 9/1/2011
Position Statement: The Yellowstone River Conservation District Council (YRCDC) encourages the construction or modification of irrigation distribution ditches in a manner that prevents the loss of water through leakage.
Introduction:
Depending upon ditch length and the substrate under the ditch, irrigation water loss can easily amount to more than half of the water diverted. This unnecessarily increases the amount of source water diverted and results in negative effects on natural stream function including water quality, fisheries, aquatic species, water temperature, etc.
Loss of water from irrigation ditches through the ditch material often reappears in the surface soils down slope. This artificial increase in available water often causes conversion of the affected down slope vegetation from native plant communities to a hydric community that is often a monoculture of sedges or cattails. Also, over time the continual wetting and evaporation in some areas results in the deposition of salts on the soil surface and can eventually result in a saline seep that is nearly sterile in terms of plant communities. It should be noted that this leakage can sometimes also result in a more positive effect such as the creation of high-value wildlife habitat or recharge of an aquifer that is being used to supply wells.
Seepage also affects the stability of the ditch structure itself and can cause ditch bank failure that can result in flooding and extensive repairs. Leakage can also cause softening of ditch side fields, roadbeds or even railroads. This results in continual high infrastructure maintenance costs and can even be dangerous to road and railroad users.
Where ditches are close to river or creek banks, the softening of the stream bank by leakage water results in accelerated erosion and siltation in the stream. Softening can also cause accelerated movement of the stream towards the ditch, often requiring repeated relocation and reconstruction of the ditch or extensive and costly stream bank armoring.
Proposed Solutions:
-Water distribution can be done most efficiently with irrigation pipelines, either buried or on the surface. This not only prevents loss of water through leakage but also through evaporation loss. Surface disturbance and use is also reduced. However the initial cost for these structures is high and may be prohibitive in some situations.
-Ditches can be lined with impervious material that prevents or greatly reduces water loss from seepage. A wide variety of materials, including reinforced concrete, vinyl membranes, heavy clay, etc. are available and can be prescribed to fit the physical and economic criteria of a particular situation.
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