Irrigation Technology is Moving us Backward

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Irrigation Technology is Moving us Backward

By: John A. Baden, Ph.D.
Posted on May 17, 2000 1

"People have come to understand that water is like gold in Montana - better, really, because gold runs out and streams flow forever, if you treat them right."

Datus Proper

"Space," from

Writers on the Range,

A book from Gallatin Writers, 1998

Each summer I switch from moving pixels on computer screens to moving pipes on hay fields. I enjoy this balance between abstract symbols and material stuff. This year, noting our low soil moisture while anticipating draught, my change came earlier than usual. I'm shutting down my Apple computers and firing up my Berkeley pumps.

Farmers and ranchers have no monopoly on "aridaphobia". Throughout the northern Rockies, I find guides, outfitters, anglers, environmentalists, and researchers worried about our spring creeks and rivers. Problems stem from the mild winter, low snowpacks, and warm days leading to early runoff. Even here, global warming isn't entirely beneficial.

Before European settlement, the aboriginal hydrograph followed a predictable pattern of high spring runoff and late summer drawdown. The result was that by late summer many creeks would warm up and dry up. Some were so low that fish were easily predated or died from elevated water temperatures and depleted oxygen.

Settlement of the mountain valleys, however, substantially changed them, and, in terms of fish and wildlife, significantly improved this situation. Using flood irrigation in early summer, settlers spread the riparian zone over far greater areas. Inadvertently, they buffered the peaks and valleys of stream flow as their flood irrigation circulated water back to the ground. This practice created a strong recharge loop further spreading the riparian areas. Ultimately this aided spring creeks and their inhabitants during late summer.

Here's one example. On our family ranch, the earliest water rights date from 1866 and our land still has miles of small, barely discernable ditches. Until the 1960s, water from early runoff was diverted through these ditches on to pastures and fields. It saturated the soil and percolated downward, raising the water table. Weeks later, from July through September, this clear, 55-degree water would return to the Gallatin River.

Yet another example is Godfrey Creek which, prior to the installation of canals in 1915, ran dry every winter. Today, however, it is perennial due to irrigation ditches and recharging the "sponge" (the groundwater table). Other creeks present the same scenario - flood irrigation recharge to water table feeds creeks and streams during late seasons. This late-season recharge counters "the black eye" given to agriculture for its high diversion rate during late summer.

Unfortunately, flood irrigating requires a substantial amount of responsible labor. And responsible workers, if one can find them, come dear. As a result, ranchers have substituted capital for labor. Labor intensive flood irrigation is gradually being replaced by wheel line sprinkler and center pivot irrigation.

These methods economize on both labor and water, but they reduce recharge into ground water. While center-pivot irrigation is 70 percent efficient, flood irrigation is less than 30 percent efficient; it "consumes" more than twice as much water. However, depending on soils and grades, the loss goes to percolation or runoff.

The efficient methods of irrigation have a serious downside. They do less to recharge springs and creeks. Economics and hydrology are moving us back toward the aboriginal hydrograph. As water fails to augment riparian areas and make its way back to the creeks, corridors can be heavily drawn down and even run dry. Ironically, in this case resource efficiency is the enemy of ecology.

Early season irrigators supply a public good when they employ hydrologically "inefficient" flood irrigation. It recharges the water table and benefits riparian areas, fish, and wildlife. However, economics tells us that when public goods are privately supplied they normally are under-supplied. Today, irrigators lack incentives to see that water makes it back to the creeks.

It would be generally beneficial to encourage farmers and ranchers to irrigate heavily during the late spring/ early summer when water is still high. This practice will give the creeks a chance to recharge, and put less stress on the water supply during the later, drier months.

We can ameliorate our water problems in two ways. First, by providing incentives for early and less efficient irrigation during spring and early summer. The goal is to recharge groundwater supplies and increase later flow to spring creeks which will foster quality habitat for fish and wildlife in late summer. Second, we can similarly encourage minimal late-season irrigation diversions which will maintain in-stream flows and cool water temperatures. This situation offers a highly positive, mutually beneficial opportunity for environmental and policy entrepreneurs.

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