Opinion: Boulder’s water supply and climate change

From observing the recent city council discussions on water, I thought it would be useful to go over some of the basics.

Boulder’s water comes from three sources: North Boulder Creek (the “Watershed” below Arapahoe Glacier), Middle Boulder Creek (flows into Barker Reservoir near Nederland), and the Colorado-Big Thompson project (from the Colorado River, includes Windy Gap reservoir).

North Boulder Creek drains the east side of Arapahoe Peak; the water is stored in multiple small lakes/reservoirs within the Watershed. The water flows into the Betasso Pipeline, starting on the west side of the Peak-to-Peak Highway near Caribou Ranch, then to the Betasso Treatment Plant near Sugarloaf. Barker Reservoir water is piped to Koessler Lake, west of Green Mountain, and then down a pipeline to Boulder Canyon and up to the Betasso plant. Some of this water runs down to the hydro plant in Boulder Canyon.

The C-BT water flows from the Colorado River headwaters through the Continental Divide to Mary’s Lake above Estes Park, down to Carter Lake Reservoir and into a pipe (formerly a ditch) to Boulder Reservoir and the treatment plant there.

Critically, Boulder has storage rights for both East Slope sources in the various reservoirs. This allows the snow runoff, which comes mainly in the spring and summer, to be made available year-round. But climate change has moved the runoff earlier in the year, reducing the value of both the snowpack and reservoir storage. Plus, hotter, drier weather has both increased evaporation and lessened total precipitation. So we are faced with a future of declining useful yield.

Colorado’s water rights are “first in time, first in right.” Thus, it’s hard and expensive to buy rights, whether flow or storage, to substitute for this ongoing loss, simply because buyers will increasingly exceed sellers as demand increases.

All C-BT water is based on rights, which are “junior” to the 1922 Colorado River Compact; Article III(d) requires the Upper Basin to deliver an average of 7.5 million acre-feet (MAF) per year to the Lower Basin state, measured at Lee’s Ferry, just below the Glen Canyon Dam. There are also treaty obligations to send 1.5 MAF/yr to Mexico, Upper Basin pre-Compact rights worth roughly 2 MAF/yr, and potentially huge obligations to the Native American tribes with land along the Colorado River. The C-BT equally allocates its water by shares owned by cities, farms, etc. A unit is nominally worth one acre-foot; each year the C-BT sets what fraction of an acre-foot will be delivered, depending on how much Colorado River runoff is expected. Climate change has caused severe droughts in the Colorado River basin and runoff has shrunk over the last decades.

So, Colorado cities that depend on post-Compact trans-mountain diversions (including Boulder, Denver and Colorado Springs) could suffer big losses. Inter-state negotiations over shrinking Colorado River supplies are finally acknowledging these realities. (1 AF equals 1 foot deep over 1 acre.)

The City staff’s forecast is that in a significantly hotter, drier future, we could lose nearly a third of our supply. That exacerbates the situation for existing residents and businesses from the 20,000 more housing units already in the pipeline, plus more non-residential, and, scarily, data centers.

This raises the question of how much the City charges new water customers and what it does with the money. Is the money collected from water tap fees adequate to purchase new flow and storage rights to make up for the amount this new development will use? And is the City using the money to purchase new rights so that existing residents are at least made whole?

As far as I know, the answers are “no.” The city updates its Plant Investment Fees (the formal name for tap fees) frequently. But to calculate the full costs of maintaining current levels of service of our water supply system, the city needs a reality-based plan quantifying how much water to acquire and how much storage to build. The standard should be to keep up with both the losses due to climate change and the dilution of existing water rights among more and more users.

So, if you thought you bought access to a fixed amount of water when you paid your water tap fee on your new house or commercial building, expect to be surprised. Unless the council makes a serious commitment now to maintain current levels of service, we are looking at a future where strict conservation measures will be the norm, existing landscape will be replaced with Xeriscape, and even interior uses will likely be restricted.