The LeBel Moratorium Letter is Wrong
Joe Gray, February 20, 2009
Mr. LeBel, in his letter sent to property owners the week of February 8th, asserts that SLCWD's Lake Level Management resolution will effectively prevent lot owners from building due to lack of water hookups. This is not true and here is why.
How much water is there if the lake level is kept above three feet?
Mr. LeBel's letter says that there will not be water available for unbuilt lots if the lake level is restricted to a three foot drop, stating that the lake already drops three feet. This is not true. Last year, a drought year, the lake dropped 2.3 feet. The previous three years the lake level only dropped 1.8, 1.6 and 1.2 feet. If we take last year's number as the worst case, then there was still 0.7 feet of water left above the 3 foot mark, or around 50 acre-feet (AF) of water. If 0.5 AF is needed per new hookup each year, then in the five month period from June through October when the lake level is dropping, each new hookup needs an allocation of 0.21 AF. This means that the 50 AF of excess water is enough for 238 new hookups. This number is, of course, not official and will certainly change based upon finishing the water supplies report described below, but is accurate enough to allay any fears of there not being any water available for unbuilt lots.
Water Supplies Report
Each year the water district is required to generate a "Water Supplies Report." This report predicts the availability of water for the current year and for the next twenty years. This report requires that the district predict how much water is in the lake to use, and how the water in the lake will be affected by climate (precipitation and evaporation for example) and water consumption. In order to do this, the district needs an accurate bathymetry study of the lake's capacity, a hydrological "water balance" model of the lake which predicts how the lake will change as a function of climate and consumption, and a target for how low the lake should be allowed to drop. It is the overall "Water Supplies Report" that will determine if there is water for future hookups.
Bathymetry Study
Two years ago Royal Gorge paid for a detailed bathymetry study of the lake. The result is essentially a contour map of the lake's bottom, which allows one to calculate the amount of water in the lake as a function of water level drop below the dam. The map also shows the water depth at any spot on the lake, and is used to show how much of the lake is dry or very shallow as a function of lake level.
Water Balance Model
The water balance model is a tool that takes daily hydrological and climate data as inputs and then predicts the lake level on a daily basis as a function of water consumption. This tool is used to predict how the lake's level will change based upon consumption, using historical climate and hydrological data from normal years and drought years. For the twenty year projection the model can also predict the effects due to climate change. This model is not yet complete, as it needs to incorporate the effects of winter ice, which may restrict the amount of free water available for consumption during the winter.
Lake Level Management
A target level needs set for how low the lake can be drawn down while preserving the health, recreation and aesthetic qualities of the lake. The target is for planning purposes to predict how much water is available for consumption, and, hopefully, to indicate when conservation measures should kick in if the lake level approaches the target.
Lake Level Target
The quality factors of health, aesthetics and recreation which lead to the lake level target can be evaluated using the bathymetry study. The evaluations are:
Aesthetics
Aesthetics is effected by how much of the lake's bed is muddy and dry. The bathymetry map shows that 10% of the lake is dry at a 2.5 foot drop in the lake's level, 12% at a 3 foot drop, 15% at a 3.5 foot drop and 23% at 4 feet. What this says is that a significant part of the shoreline is dry or muddy at a 3.5 foot drop, and almost a quarter of the lake is dry at 4 feet. For aesthetic reasons the lake's water level should be kept above a three and a half foot drop.
Recreation
For recreational use the important factor is how much of the lake is too shallow for swimming or boating, and how deep is the channel between lakes. For swimming the water should be at least two feet deep. The bathymetry data shows that 30% of the lake is less than 2 feet deep at a drop of 2.5 feet below the dam, 37% at a drop of 3 feet and 43% at a drop of 3.5 feet. Essentially, over a third of the lake is a wading pool if the level is allowed to drop below 2.5 feet. For swimming, the lake level should be kept above 2.5 feet.
The lake should be at least 18 inches deep, and the channel at least 12 inches deep for most boating purposes. The lake needs to be even deeper for sailboats. At a drop of 2.5 feet only 23% of the lake is below 18" and the channel is 18" deep. At a 3 foot drop 30% of the lake is less than 18" deep and the channel is only 12" deep. At a drop of 3.5 feet, 37% is less than 18" deep and the channel is only 6" deep. At 4 feet the channel is dry. For recreational reasons the lake level should be kept above a three foot drop.
Health
The health of the lake is most effected by the surface water temperature, which is in turn will stimulate algae growth and loss of dissolved oxygen which will kill aquatic life. How much the sun will heat the lake is a function of the depth of the water in an inverse relationship. For example, water that is 2 feet deep will heat up half as fast as water 1 foot deep. Similarly 3 foot water heats 1/3rd as fast. A measure of the heating potential of the lake's surface can be made by calculating the average of the inverse-depth of the lake. For example, add up the area at 1 inch deep, plus 1/2 times the area at 2 inches deep, plus 1/3 the area at 3 inches deep, etc. If this measure is normalized to a coefficient of one at the dam level, then the coefficient is 1.5 (50% more heating potential) at a 2.5 foot drop and is 2.1 at 3.5 feet. This means the heating potential goes up from 50% higher at 2.5 feet to 110% higher at 3.5 feet. This jump from 50% to 110% indicates that for health reasons the lake level should be kept above a 3 foot drop.
The conclusion is that for aesthetic, recreational and health reasons the lake level should not be allowed to drop below three feet.
Conclusion
Mr. LeBel's letter has many inaccuracies that have been addressed here. Those include: