Mark L. Johnson
Water Woes I
Updated: Jul 24, 2021
Lake Mead-41% Full
White Paper 6-Alternative Management Paradigms for the Future of the Colorado and Green Rivers casts doubt on the ability of the current western water bureaucracy to sustainably manage the Colorado River. This white paper was published by 12 scientists at the Center For Colorado River Studies-Utah State University.
The major conclusions gleaned from White Paper 6 are:
Millennium Drought (2000-2018) is probably the new normal with average annual Colorado River flow at 12.4 million acre-feet per year (maf/year) (1).
Projected Upper Basin consumptive use is too high and current Lower Basin shortage reductions are too low.
Climate change (study used 6.5% decrease in flow with each degree of Celsius rise in temperature) exacerbates the supply/demand imbalance.
Law of the River does not provide the flexibility required to sustainably manage the Colorado River system (1).
Twenty-four alternative management strategies are presented including the scenario whereby Lake Powell and Lake Mead are consider as a single reservoir (2).
(1) As we learned in Know Your H2O Part VII-Colorado River, the Colorado River Compact provides for 7.5 maf/year for the Lower Basin (CA, AZ & NV), 7.5 maf/year for the Upper Basin (CO, NM, WY & UT) and 1.5 maf/year for Mexico per 1944 Treaty. This totals 16.5 maf/year and is higher than the Millennium Drought average annual flow of 12.4 maf/year
(2) Lake Powell Capacity = 24.322 maf (currently 39% full at 9.416 maf)
Lake Mead Capacity = 26.151 maf (currently 41% full at 10.614 maf)
White Paper 6 Figure 9.5 (below) demonstrates the need to keep Upper Basin consumptive use at reasonable levels and increase the shortage amounts for the Lower Basin in order to keep the combined storage in Lake Powell and Lake Mead at acceptable levels.
What does this mean for Arizona?
The current maximum shortage reduction for the Lower Basin (Lake Mead goes below elevation 1,025 feet) is 1.1 maf/year. Referring to Figure 9.5, Lower Basin shortage reductions need to potentially range from 1.375 maf/year to 3.0 maf/year for an average of about 2.2 maf/year or twice the current shortage reduction.
Arizona's current maximum shortage reduction is 0.72 maf/year (26% of its 2.8 maf/year allocation). If the scenarios in Figure 9.5 come true, Arizona could be required to cut back about twice that amount or 1.44 maf/year (51% reduction)!
What does this mean for Marana?
We learned in Know Your H2O-Part X-Marana Water & Tucson Water that in 2019 Marana Water had the following statistics:
Water Delivered-2,366 acre-feet
Average Daily Demand (Delivered)-2.1 million gallons per day
Gallons Per Capita Per Day (Delivered)-95.6 gpcd (using 2.7 persons per customer)
Average Residential Home Consumption-0.3 acre-feet/year/lot
Central Arizona Project Delivery Contract-2,336 acre-feet/year
Total Renewable Supply-4,017 acre-feet/year (2,336 CAP + 1,681 Effluent)
This data shows that Marana Water has only 1,651 acre-feet/year (4,017-2,366) of renewable water supply (CAP & Effluent) remaining. That is equivalent to 5,500 homes (1,651/0.3)!
If Marana's CAP Allocation is cut by 51% to 1,145 acre-feet/year, there is only enough renewable water to serve about 1,500 additional homes!
Amazingly, if you go to Marana's Subdivision Activity Report it indicates that Marana has approved subdivisions with a total of 56,443 residential lots. Of that amount, 23,538 lots have been platted and 4,226 of the platted lots are vacant. Non-platted lots total 32,905. This means there are 37,131 (32,905 + 4,226) residential lots approved. That equates to 11,139 acre-feet/year (37,131 x 0.3). Where on earth is all this water going to come from?
Marana will tell you they have an Assured Water Supply (AWS) of 7,580 acre-feet/year. But Marana Water existing water use and future water use from approved subdivisions far exceeds the AWS. Furthermore, 3,394 acre-feet/year of the AWS amount must be replenished from the Central Arizona Groundwater Replenishment District (CAGRD). From Know Your H20 Part-VI-Groundwater Management Act it is clear that CAGRD has over-committed and is relying on future water transfers that may never happen and will most likely be subject to the same shortage reductions. Plus the cost of CAGRD water is very high at $746/acre-feet versus CAP water at $152/acre-feet.