In August and January of each year, the Bureau of Reclamation (Reclamation) releases a projection of what Lake Mead on the Colorado River could look like in the next 5 years. You can find their projections HERE. As we look towards the new update, let’s take a look back on some highlights of what the August 2020 projection contained. Since this is an intensive question that has far-reaching implications for all western states subject to the Colorado River Compact (see the LWS blogs on 11/17/20 and 5/4/21) and has many complexities and moving parts, a model was used by Reclamation to assess this question. However, if you read the release on their website, the numbers and terms start flying, such as “113 Full hydrology traces,” “31 Stress test hydrology traces,” “Shortage/Reduction-2nd level at Lake Mead,” and so many more. That’s a lot to take in and understand all at once! Let’s break it down and explore it together.

First, let me provide a simplified overview of the model. The model developed by Reclamation is called the Colorado River Simulation System (CRSS). It models the flows into and out of 12 reservoirs along the Colorado River. There are various timeframes over which hydrologic information is gathered or reconstructed. For these results, there were two timeframes used to make the 5-year interval projections. Since 1906, natural flows have been recorded continuously through 2018 and represent the input to the model. From this 113-year dataset, 113 sequences of 5 years were assembled from sequential months (e.g., 1906-1910, 1907-1911, etc. through 2014-2018). These sequences are called traces. The specific traces were created by using a methodology created by the Western Area Power Administration. As a power generator, they need to know how much flow is expected to be available so they can anticipate and create power for their region, which means accuracy of these traces need to be as accurate as possible! However, in recent years lower flows have been recorded, which could have significant impacts on power production. Using data from 1988-2018, 31 traces were made under what was called the “31 Stress Test” simulations. This allows the model to be used for evaluating what flows may look like under lower flow conditions.

With all the data resulting from this modeling of 144 traces (113 traces of historic data and 31 traces of estimated reduced flow traces), statistics are the best way of understanding the results in a meaningful way. Reclamation’s article does this by showing a table with various results for both Lake Powell and Lake Mead. Looking at the results for the full hydrology, a normal volume of water in Lake Mead happened an average of 61% of the time. However, over the course of the simulations around years 4 and 5 across all 5-year traces, a significantly lower volume of water was observed with shortage conditions up to 53% of the time in those years. These simulated shortages were exacerbated in the stress hydrology simulations where normal volumes were found only 54% of the time and shortage conditions were simulated to occur up to 77% of the time in the last year of the 5-year simulation. Another concerning result from the table is the occurrence of a shortage/reduction at the 2nd Level, which is related to a water level below the estimated minimum level needed to generate power. From the table, this has an average occurrence of around 10%.

While these are just simulations based on past information, it does give us an idea as to what the future may hold. If additional stresses on water availability occur on the Colorado River, solutions will only come at the nexus of many different disciplines. Examples of these include application and development of new technology both on the supply side and the demand side, cooperation between many and diverse stakeholders, application of local knowledge to avoid pitfalls, and clear communication among groups are just a short list of what and who will need to be a part of the solutions.

Beyond the theoretical role of Reclamation’s predictive tool, real world crisis may be coming to users along the Colorado River system. Lake Mead water levels are dropping to historic lows (see recent Denver Post article HERE) which will result in raising the tier restrictions under the Colorado River Drought Contingency Plan (DCP), discussed in the May 11, 2021 LWS blog. Not only is there the distinct likelihood of continuing increased restrictions on use of Colorado River water through the DCP, but there are also groups calling for even tighter restrictions on Colorado River use in the hopes of restoring water levels in Lake Mead (Denver Post, July 16, 2021).

LWS has played a role in bringing more sustainable water supplies to serve growing needs in the western United States. LWS has assisted the Parker and Water Sanitation District with the permitting, construction, and current operation of Rueter-Hess Reservoir, which has brought much-needed renewable resources to the district. LWS is currently working on a collaborative renewable water supply project in eastern Colorado that will increase surface water storage and provide renewable water to eastern plains farming and to Front Range municipalities (see LWS blog series on “Integrated and Sustainable Water Management…”).

If you have any water resources issues, LWS can help. For more information on this subject or any Western water rights issue, please contact us for help at 303-350-4090 or by email.

Bruce Lytle, P.E. bruce@lytlewater.com

Chris Fehn, P.E., P.G. chris@lytlewater.com

Ben Bader ben@lytlewater.com

Anna Elgqvist, E.I. anna@lytlewater.com