Archives 2019

Spring has sprung (hasn’t it?), and water’s flowing downhill

Spring has sprung (hasn’t it?), and water’s flowing downhill

During Central’s April board meeting, Hydraulic Project Operations Manager Cory Steinke engaged board members and everyone else at the meeting in an exercise to illustrate the complexity and difficulty of managing water supplies.

Each participant was given a stack of pennies that represented the existing – and future – water supply in storage at Lake McConaughy.

The point of the exercise was to complete a four-year cycle of inflows and releases without 1) running out of pennies (water); and 2) leaving insufficient space for additional pennies (inflows) resulting in a “spill” of valuable water.  (A “spill” is a release of excess water from a reservoir.)

During the exercise, Steinke was repeatedly asked for more information pertaining to various snowpack conditions, irrigation demand, upstream storage reservoir conditions, weather forecasts, etc.  But a crystal ball was not part of the game, just as water managers usually cannot see clearly very far into the future.  They must rely on the best available information – both short-term and long-term – on which to base their decisions and even the best, most recent information, can be subject to rapid change.

Operational projections begin with known quantities of water in storage at the beginning and end of any particular cycle.  Despite having access to the latest forecasts, any unexpected changes to any of the numerous factors that influence water management operations could leave the participants “penniless,” or at the other end of the spectrum, having too many pennies in the bank.

One need look no further than the recent events afflicting eastern and northeastern Nebraska and western Iowa.  The flood damages were the result of a series of unlikely events occurring simultaneously, creating a scenario that overwhelmed manmade dikes, dams and operational plans and caused creeks and rivers to swell out of their banks.

A coincidence of “unlikely events” is not the same as “impossible events;” even planning that prepared for “unlikely events” and “maximum probable floods” was overcome by the capriciousness of weather and Nature’s unrelenting power.

While flooding along the Platte River did not occur in central and western Nebraska, spring is the time of year when water managers keep particularly close watch on conditions in the upper Platte River basin.

The U.S. Bureau of Reclamation, which manages a series of reservoirs on the North Platte River in Wyoming and monitors snowpack/snowmelt conditions in the North Platte and South Platte drainage basins, recently released its projections for runoff.

The April forecasts indicate the spring snowmelt runoff will be above average.  Total April through July runoff in the North Platte River Basin above Glendo Dam in Wyoming is expected to be 1,005,000 acre-feet (a-f) which is 111% of the 30-year average.

As of March 31, storage content in the North Platte Reservoirs was 1.8 million a-f, which is 110% of the 30-year average.  The total conservation storage capacity of the North Platte Reservoir System is approximately 2.8 million a-f.  At this time, the Bureau is not anticipating a spill of water from Pathfinder Reservoir.

In the South Platte River basin, snowpack conditions are currently at, or slightly above, normal for early April.

Prior to the projections, Central had noticed the increasing snowpack and began making adjustments to water operations to leave space in Lake McConaughy for any extra water released from the upstream reservoirs.

However, the South Platte River remains, as always, a wildcard.  With only minimal amount of off-stream storage capability in Colorado, the South Platte remains susceptible to rapid snowmelt runoff and heavy spring rains that could cause high-water events in western and central Nebraska after it joins with the North Platte River east of the City of North Platte.

Central will continue to monitor developments in the North and South Platte River basins this spring and is tailoring operations to developing conditions, including precipitation forecasts for April and May that call for increased chances for above normal precipitation throughout most of the Platte River Basin.  Lake McConaughy has no designated flood pool (an amount of space in a reservoir designed for flood control used to regulate floodwaters), other than gradually rising restrictions on maximum elevation during the spring, but the reservoir has been operated during high-flow periods when necessary to mitigate downstream flooding that is often the result of high South Platte River flows.

But as demonstrated by recent events, Mother Nature sometimes has plans of her own that overwhelm human efforts to manage our rivers and streams.

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