The above display shows the Aberdeen-Springfield Canal's path and its seepage loss through specific areas. The Canal loses to seepage and evaporation roughly half of the water taken from the Snake River by the time it reaches its end point near Neeley, 67 miles downstream. Any unlined canal suffers similarly, with stretches through sand, gravel or fissured rock increasing loss rates. In the map above, the gravelly area north of Moreland is a big loss area, with a long stretch of canal north of Springfield which traverses broad stretches of lava knolls likewise subject to heavy water loss.
The inefficiency of canals, to someone technically inclined, might be solved by lining or cementing high-loss areas—"puddling" was a rudimentary variation of this used at the end of most any canal's construction, entailing "stuffing" fissured areas with a clay-water mix, a technique somewhat akin to spackling drywall or mortaring cinderblock joints. But the problem of seepage, while presenting a difficulty for canal managers and appearing to be wasteful, from a wider perspective may not be a problem at all, for water lost by the Aberdeeen-Springfield canal mostly returns to the aquifer before emerging once again at the "Snake River Reach", a series of streams from Pingree to American Falls that enter the river. The canal's loss, over 600 cfs, is roughly equivalent to a quarter of the outflow at that Reach.
Just as the Aberdeen-Springfield Canal splits into two smaller canals, the High Line and the Low Line, north of Grandview, the question regarding water loss also diverges into two: should the canal "save" surface water by lessening seepage—in which case aquifer recharge is lessened, or continue to "waste" water at the surface while adding to groundwater supply. If you remove the cost to the canal of lining problem areas, then preventing seepage is beneficial for Aberdeen-Springfield water users but a losing proposition for downstreamers.
That conundrum is just one of many in the fight over water in southern Idaho, most recently culminating in a water curtailment of a large amount groundwater acreage in the eastern part of the state, that area irrigated by pumpers with "junior" water rights after 1951 which are secondary to "senior" water rights from an earlier, flood irrigating era. In the legal fray over water that is a primary theme for not just Idaho's but the entire West's development, the ruling stricture for water distribution is called prior appropriation—first in time, first in line—and is akin to two children jumping in your car, the eldest yelling "shotgun" in order to get the best seat. The Twin Falls area canals, in its case against groundwater-pumping sprinkler irrigators, called "shotgun" first, while the oldest southeast Idaho canals, all much smaller in carrying capacity, predate Twin Falls water rights. Those canals, like Twin Falls, could ultimately also turn against their pumping neighbors to the north if a sufficiently droughty era ever severely diminished flows.
Twin Falls' users status on the tail end of the aquifer gives them the proverbial position of being "a Catholic at the end of a Mormon ditch," any shortfall of water serving as fodder for an accusation against upstream users. Prior to sprinkler irrigation, such squabbles were fairly easy to mediate, with the youngest water rights being shut off on dry years, with the next youngest being curtailed as river flow further lessened, etc. etc. Almost every water year, prior to reservoir building on the Snake, ended up in some rights being curtailed, with drought years reaching back to curtail even the oldest rights.
Sprinklers changed that simple equation, and unlike flood irrigation took water from the aquifer but didn't replenish it. Idaho law, after decades of allowing sprinkler irrigation to spread unfettered, eventually put a moratorium on new wells and tied aquifer use to surface water use, complicating the inherent disputes over water rights. This allowed downstream users at Twin Falls to claim upstream groundwater pumpers adversely affect aquifer levels and consequent outflows rightly due them, as senior water rights holders.
The Twin Falls Canals, which like the Aberdeen-Springfield also traverse rocky, fissured terrain, also lose roughly half their intake through seepage, but their losses, while recharging the aquifer much as the Aberdeen-Springfield and other eastern Idaho canals do, come at the downstream end of the underground reservoir and hence, unlike upstream canal recharge, isn't retrievable by the Snake River waterusers within the system. Whatever underground storage their seepage creates dissipates away from the reach of irrigators, unlike that of southeast Idaho's which becomes available for those below the recharge outflow.
The Twin Falls Canal recently lined a particularly porous section of its system, spending $800,000 to line a three-quarter mile stretch. The effort was expected to save 6500 acre feet of water per year, a small portion of the million plus acre feet it delivers to over 4000 shareholders. The company plans to complete four to five more miles as grant money and financing becomes available.
The graph below displays the reason for Department of Water Resources'—and irrigators'—concerns regarding longterm water usage and storage. From 1912 to 1952, during the flood irrigation era, discharges at Thousand Springs at the Snake River Aquifer's endpoint rose, while in the following sixty years they fell to approximately the original, pre-irrigation level. The trend doesn't bode well for future water use.
As difficult as it might be to measure hidden, undergound water in relation to the relative ease of discerning aboveground reservoir contents and stream flows, the correlation between sprinkler irrigation's onset (and furrow irrigation's demise) follows outflows so closely that it's hard not make a causal connection between pumping and aquifer water loss.
Because water in the aquifer moves slowly—one 1969 estimate is 13.5 feet per day—losses and recharge can be difficult to measure. The Aberdeen-Springfield problem areas lay only roughly six miles away from the outflow area, its seepage reaching the river in just a few years, but water that once drained from the Lost Rivers, but which has been used by irrigators for nearly a hundred years now, would take roughly forty years to reach the Thousand Springs area near Hagerman, the primary outlet, along with the Snake River Reach, for aquifer drainage.
Pumpers on the desert between Arco and the Snake began drawing water in the 1950s but didn't fully replace flood irrigation, which creates aquifer recharge, for another three decades. If there is a direct correlation between eastern Idaho pumping and aquifer outflows, but water levels elsewhere in the aquifer should soon show increasing evidence of being affected.
Making correlations with water isn't easy—pour two streams into a bucket and try to determine which water is which and you'll have an idea where an hydrologist has to start his calculations. A casual observer sees full reservoirs and assumes there is plenty of water, but an hydrologist has to consider longterm effects and causes and predict future trends. If those in charge, i.e. the Department of Water Resources, were to wait for well levels to drop before taking action it would be too late for action–and they would be cursed for not doing their job.
The hard evidence in this blog derives from "CONSIDERING REGIONAL AQUIFER EFFECTS OF SEEPAGE LOSSES FROM THE ABERDEEN-SPRINGFIELD CANAL WHILE MEASURING
THE SYSTEM UNDER MAXIMUM DEMAND CONDITIONS," by Heather Rice
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