Moscow Water Supply Alternatives
Moscow residents are continuing what has been a long, ongoing, discussion of water supply issues in the Palouse Basin. I recently ran across a study which provides some information that should be useful for that discussion. The following information is taken from the report Reconnaissance Report, Palouse River Basin, Idaho and Washington by the US Army Corps of Engineers, dated March 1989. Click here to see the table of contents of the report (page 1, page 2).
The Corps Reconnaissance Study
The water supply options shown below are not being seriously considered at this time, and for reasons I will outline below, they should probably not be considered seriously. However, since I hear ideas like these mentioned occasionally, I thought the results of this Corps study ought to be more widely known. The purpose and scope of the Corps study are stated in the report:
The report examines four water supply alternatives:
The Corps report also looks at two smaller dams, one on Paradise Creek just east of Moscow, and another that would recreate the now defunct Robinson Lake. The Corps viewed them as flood control rather than water supply structures, but since I have also heard people talking about these, I will include thee in my discussion of the possible projects.
Harvard and Laird Reservoirs
Because these two alternatives have elements in common, I will talk about them together. Both of these projects were designed to provide 25,000 acre-feet of water for use in Moscow and Pullman, which was the Corps estimate of water needed by the two cities "in the next 30 years".
The 110 foot high Harvard Dam would be 1/2 mile above Harvard, Idaho. The reservoir would cover 2,673 acres when full. In addition to the 25,000 acre-feet of M&I water, the reservoir would have 75,000 of flood water storage, which would benefit downstream places such as Palouse and Colfax. Harvard Dam would also have a 1.6 MW hydropower facility.
The Laird Park Dam would be an alternative to the Harvard site. The 209 foot dam would be located above the Laird Park campsites, just below the junction with Strychnine Creek. The full reservoir would cover 1,075 acres, and provide 45,000 acre-feet of flood storage above the 25,000 allocated for M&I use. The hydropower plant was 1.1 MW.
Water for use in Moscow and Pullman would be released from either of these dams, and flow in the natural river channel to a point just above the Town of Palouse, Washington. The water would be diverted from the river, run through a water treatment plant, and piped south to Moscow and Pullman along railroad rights of way.
Pipeline from Snake River
This alternative would pump water from Lower Granite Reservoir, up Wawawai Canyon to a water treatment plant, and then via pipeline to Moscow and Pullman. This scale of this alternative was slightly smaller than the Laird and Harvard alternatives -- the Corps assumed that the cities would need 20,000 acre feet of water per year. The pump lift would total 2,064 feet, and the pipeline length would total 21.6 miles.
Pipeline from Dworshak Reservoir
This alternative would require a total of 55 miles of pipeline. The pump lift to get the water over the ridge between Dworshak and the proposed water treatment plant near Kendrick would be 1,715 feet. The lift from Kendrick to Moscow and Pullman would be 700 feet. This pipeline was scaled to an average capacity of 20 million gallons per day (21,500 acre-feet per year). The Corps noted that diverting this amount of water from Dworshak Pool would measurably decrease hydropower generation at Dworshak Dam, although a small portion of that power could be recovered with a small hydropower plant where the pipeline drops into Kendrick.
Paradise Creek Dam
The proposed Paradise Creek Dam would be just to the northeast of Mountain View Park. The, dam would be 2,850 feet long, and rise to 37 feet above the streambed. The Corps intended this dam and reservoir as a flood control structure, to benefit both Pullman and Moscow. It could hold 1,500 acre-feet of floodwater, and when full would cover about 40 acres. The Corps did not design hydropower facilities for this site, and it is doubtful whether hydropower generation would be feasible at a facility this small.
Since the Corps designed this project as a flood control facility, it did not consider the plumbing or the cost estimates for delivering this water for municipal use. Whether the project could be used for municipal water purposes is questionable, given the likely loads of silt and agricultural chemicals that would be inevitable at this site. Siltation would either be an added cost, or would limit the life of this project.
Robinson Lake Dam
The Corps also looked at the old Robinson Lake dam site as a possible place to put a flood control structure. The proposed structure would be located 700 feet downstream form the site of the old dam. The structure would be 1,175 feet long, and about 110 feet above the streambed. The reservoir was designed for 4,000 acre-feet of active flood control storage, with a surface area of 160 acres. Again, the Corps did not design hydropower facilities for this site, and it is doubtful whether hydropower generation would be feasible at a facility this small.
Since the Corps also designed this project as a flood control facility, it did not consider the plumbing or the cost estimates for delivering this water for municipal use. If the water were used for municipal purposes, it would have to be delivered via the natural channel of the South Fork of the Palouse River. Whether the project could be used for municipal water purposes is questionable, given the likely loads of silt and agricultural chemicals that would be inevitable at this site. Siltation shortened the life of the original Robinson Lake, and likely would do the same for a replacement reservoir.
The Corps presented cost estimates for each of these alternatives in its 1989 report. I have updated these cost estimates to account for the amount of inflation between 1989 and 2004 using the consumers price index. The costs are truly astounding. The total investment cost ranges from $71 million for the Snake River pipeline up to $186 million for the Harvard Dam and pipeline. The corresponding annual costs (net of any hydropower revenues) range from $13.4 million to $20.6 million. I suspect that costs would be even higher if they were estimated today, because land development in the intervening 15 years will have pushed land acquisition costs up by more than the rate of inflation.
To put these cost estimates in perspective, keep in mind that the total budget of the City of Moscow water department is currently about $2 million.
The Corps concluded that if the region needed to seek an alternative water supply to replace a depleted groundwater supply, the most feasible alternative would be the Snake River pipeline. The next most feasible alternative would be the Laird Park Dam and pipeline, especially if the flood control benefits were significant. I don't see that anything has happened in the last 15 years to change that conclusion.
I note, however, that this would imply a doubling or tripling of water costs to the region. If the rates charged to water customers were to double or triple, real water conservation would occur. If water rates were raised to reflect the likely costs of importing water into the region, demand could easily drop to where we didn't need to import that water, and drop to the point where we were no longer depleting the aquifer.
That would be a painful solution. However it would be an absurd solution to deplete the aquifer through profligate water use, build an expensive system to import water to the region, and then find that we are then committed to those same high water costs that could have caused us to use the aquifer more frugally.
The route that the Palouse Basin Aquifer Committee is now taking -- investigating the possibility of aquifer recharge -- looks to me like a much better idea than any of the grandiose schemes in the Corps study. Issues of cost, water quality, siltation, etc, all suggest that aquifer recharge would be a better alternative than trying to adapt the Paradise/Robinson small reservoir approach to municipal water supply.