EDITORIAL: Your Thoughts About Water? Part Five

Read Part One

Disclosure: Although I currently serve as a volunteer on the San Juan Water Conservancy District board, the following editorial expresses only my personal opinions, and not necessarily the opinions of anyone else on the SJWCD board, nor of the board as a whole.

If you’ve had a chance to review, and perhaps comment on, the draft ‘Strategic Plan’ currently being written by the San Juan Water Conservancy District board, you have seen that the District lists several projects it plans to work on over the next decade or so. Most of the projects are modest, but one — the San Juan River Headwaters Project, also known as the Dry Gulch Reservoir — might be one of the largest infrastructure projects ever constructed in Archuleta County.

Perhaps, the largest.

As was mentioned in a previous installment of this editorial series, the San Juan Water Conservancy District was created in 1987 by a vote of Archuleta County residents. It’s governed by a volunteer board of directors who are appointed by the local Water Court judge.

For the past couple of decades, the District board has been focused almost entirely on the job of creating a water reservoir in the Dry Gulch Valley, northeast of downtown Pagosa Springs. The job has been made somewhat more difficult due to lack of enthusiastic community support for the project. Even the Pagosa Area Water and Sanitation District (PAWSD) — the District that was originally spearheading the reservoir project and that is co-owners, with SJWCD, of the former Running Iron Ranch property where the reservoir might be built — decided to take the project off its official ‘Capital Improvement Plan’, leaving SJWCD holding the water bag, so to speak.

SJWCD has a very modest annual budget funded by District taxpayers in the form of a property tax mill levy — about $75,000 a year — which seems even more modest when compared to the $60 million or so it might cost to build a reservoir at Dry Gulch.

Nevertheless, folks who know a lot more about water than I do seem to have faith that the reservoir will get built someday. Here’s a quote from the Southwest Basin Roundtable’s 2015 ‘Basin Implementation Plan’ which became part of the state’s ‘Colorado Water Plan.’

The Dry Gulch Water Storage Facility Project is a noteworthy project for providing municipal water supply. It will incorporate both consumptive and non-consumptive uses for state and local purpose. The primary proponent of the project is presently San Juan Water Conservancy District. The off-stream facility will have storage capacity of up to 11,000 acre-feet. The project will utilize gravity flow and syphoning to fill and maintain water levels; this is a cost effective and environmental friendly approach. The project is the preliminary stages and is currently resolving land ownership issues and securing funding.

That summary was written in 2015. To date, the land ownership and funding issues have not yet been resolved.

Another thing that hasn’t been resolved, in my opinion, is the question of water loss in local reservoirs. Yesterday, we mentioned that Lake Mead — the largest reservoir in the US — loses perhaps 800,000 acre feet of water annually, to evaporation. To put that number in perspective, the State of New Mexico is allotted about 840,000 acre feet per year from the Colorado River, for the entire state.

Lake Powell, the second largest reservoir in the US, loses somewhat less water to evaporation, but was built in an area of porous sandstone. One recent report commissioned by the Glen Canyon Institute estimated that Lake Powell loses 300,000 acre feet of water to seepage, every year. The same report suggests that draining Lake Powell and storing the water in Lake Mead would greatly benefit the Colorado River, by eliminating both the evaporation and seepage that plague Lake Powell.

In other words, some scientists are making a rational argument that “One Reservoir is Better than Two.” (The opposite, perhaps, of the argument that “Two Heads are Better than One”?)

We currently have one massive reservoir in Archuleta County — Navajo Lake, the fifth largest reservoir in the Colorado River Basin system, built in 1962. But the lake sits in the far southwestern corner of the county, and most of it resides in New Mexico, and thus, the water is not available to Pagosa Springs residents. But could we figure out approximately how much water it loses to evaporation?

Lake Powell has a surface area of about 163,000 acres, give or take, and one calculation suggests that it loses about 390,000 acre feet of water yearly to evaporation.

Navajo Lake has a surface area of about 15,600 acres — roughly one-tenth the size of Lake Powell. So Navajo Lake might be losing around 39,000 acre feet of water to evaporation, annually.

Navajo Lake, on the Colorado-New Mexico border.

To get a full picture of this problem, we note that evaporation takes place at the lake’s surface. A very deep but narrow lake will lose less water to evaporation than a broad, shallow lake that contains the same amount of stored water. Ideally, when you plan a reservoir, you want to pick a site that allows for a narrow, deep lake… if you want to minimize the evaporative loss.

What might the evaporative loss be, from a future reservoir in the Dry Gulch Valley? Say, for example, an 11.000 acre-foot reservoir, built in a shallow, sloping valley. Here’s a very rough (unscientific) estimate, since I’ve not yet come across a scientific estimate. (They say you should never do math in public, but what the heck.) A report by Harris Engineering estimated the height of a dam for an 11,000 acre-foot reservoir in the Dry Gulch Valley at about 100 feet.  So we might guess the deepest parts of the reservoir, near the dam, might be about 90 feet deep. At the opposite end of the reservoir, the water level becomes zero feet.  That would make the average depth maybe 45 feet?

If the reservoir holds 11,000 acre feet and it averages 45 feet in depth, the surface area would be about 250 acres… a tiny fraction of nearby Navajo Lake. Nevertheless, if we use our Lake Powell evaporation estimate as a guide, it would appear that an 11,000 acre-foot reservoir in Pagosa Springs might lose about 630 acre-feet of water, annually, to evaporation.

Is that a significant number? 630 acre-feet?

According to Pagosa Area Water and Sanitation District documents shared last February, PAWSD sold about 1,237 acre-feet of water to its ratepayers last year — less water than they sold in 2007, for example, and much, much less than they sold in 2001. The people of Pagosa Springs have done an excellent job of conserving our water resources, even as the Archuleta County population has grown.

But comparing these two numbers? 1,237 acre-feet delivered to customers… vs… 630 acre-feet evaporated into thin air? Is it possible that a new reservoir — an 11,000 acre-foot reservoir in the Dry Gulch Valley, for example — would evaporate away half of the water PAWSD is currently selling to its customers?

And the benefits from such a reservoir would be…?

Read Part Six…

Bill Hudson

Bill Hudson

Bill Hudson began sharing his opinions in the Pagosa Daily Post in 2004 and can’t seem to break the habit. He claims that, in Pagosa Springs, opinions are like pickup trucks: everybody has one.