September 2005
A key task in the preparation of the 2006 Lower Colorado Regional Water Planning Group (LCRWPG) Plan for the Lower Colorado Region (Region K) is to estimate available water supplies within the region.
Water supplies in the Lower Colorado Regional Water Planning Area (LCRWPA) are available from 10 aquifer systems and alluvial groundwater and 6 river and coastal basins. The Colorado River Basin makes up the single largest source of surface water for the region with large volumes of water available from both run-of-river (ROR) diversion rights and water stored in reservoirs. Water available in the LCRWPA was found to total nearly 1,300,000 ac-ft/yr, of which over 73 percent is from surface water sources.
Initial surface water supplies for drought of record (DOR) conditions for the Colorado River Basin were developed using the Texas Commission on Environmental Quality (TCEQ) November 2004 WAM (Water Availability Model) Run 3. This conservative model predicts water availability under DOR conditions and assumes maximum surface water diversions with no return flows to streams. However, review of the model results demonstrated a shortage of firm yield water in reservoirs in Region F and brought about a need for coordination between the Region F Planning Group and the LCRWPG. The result was a WAM modified to include a planning assumption whereby downstream water rights holders would not call on inflows from Region F during the planning period. This “No Call” assumption does not have legal standing and does not impact the seniority of owner’s rights, but simply is a more accurate reflection of how water is managed in the basin. This model produced firm yields for the Colorado River Basin that would be used by both Planning Regions in order to avoid conflict in later phases of the planning process. Information from WAM runs were used when available for determining firm supplies in other basins of the LCRWPA. Local supplies (stock ponds, etc.) were assumed to be consistent with numbers previously evaluated in the 2001 Plan.
There are a lot of remaining issues and concerns regarding the accuracy of the “No Call” model, some of which are explained below:
· “No Call” model was introduced late in the process and was not satisfactory to all members
· “No Call” needs much further refinement as a model and the refinement is continuing; it just has occurred too late to be incorporated fully in this effort
· “No Call” makes many assumptions that will require significant changes in current rights and agreements that may or may not occur
· It is the best available information for completion of this effort
Groundwater supplies were developed from the best information available from Groundwater Availability Models (GAMs), local information from Groundwater Conservation Districts (GCDs), or information from the previous LCRWPA Plan (2001). Both surface water and groundwater availability for the LCRWPA is shown in the Table 1.
Table 1 Groundwater and Surface Water Supplies Available to the LCRWPA
In comparison to water availability in each decade described in the 2001 Plan, total water availability for every decade in this Plan (2006) is higher. Figure 1 shows a comparison of the water availability used in developing the 2001 Plan to the water availability for the 2006 Plan (supplies from other regions were not included in this comparison).
Figure 1: LCRWPA Water Availability – 2001 vs 2006
The total amount of water supply for the water user groups (WUGs) in Region K is less than the total available water to the region presented in Table 1, since the water supply for the WUGs is limited by current needs, location relative to the source, and infrastructure limitations. There is water available in Region K that is not currently being used by WUGs because they do not have shortages, or “needs” right now, or they do not have the means to utilize the source at this time.
Water Shortages
The water supplies and projected demands for each WUG were compared to determine where needs are expected to occur. The comparison identified 99 WUGs that would have projected water deficits by the year 2030 under DOR conditions. An additional 19 WUGs are shown with projected water deficits arising between 2030 and 2060.
The estimated water needs under DOR conditions for all of Region K is approximately 281,000 ac-ft/yr in 2030 and 557,000 ac-ft/yr in 2060. This identified shortage is based on availability estimates, which exclude water available from LCRA on an interruptible basis and water available as a result of Austin’s return flows to the Colorado River. Water needs have been identified in all of the six water use categories, as shown in Figure 2, which illustrates the distribution of the number of WUGs with identified water needs in the years 2030 and 2060. Figure 3 shows the magnitude of the identified needs by water use category for the years 2030 and 2060.
Note in Figures 2 and 3 that the category with the largest number of user groups with potentially unmet needs and the greatest total 2060 regional shortage is in the category of municipal users. Irrigation shortages, which are expected to be the largest shortage in 2030, are reduced in 2060.
Figure 2: Number of LCRWPA Water User Groups With Needs
Figure 3: LCRWPA Identified Water Needs by Category of Use
Several management strategies were assembled to provide for the unmet water needs identified above. Many of the shortages were met with the extension of existing contracts, new contracts, or allocation of existing supplies. Other strategies are more extensive and will require the implementation of conservation measures or the construction of additional infrastructure. Below is a list of the recommended strategies to meet all of the needs in Region K.
Regional strategies:
· Utilization of return flows
· Expansion of existing groundwater supplies
· Development of new groundwater supplies
· Transfers and allocations
· Temporary overdraft of aquifers
Lower Colorado River Authority (LCRA) strategies:
· Irrigation water rights amendments
· New contracts
· Contract extensions and amendments
· Contract reductions
City of Austin (COA) strategies:
· Conservation
· Reuse (Direct and Indirect)
· LCRA contract renewals
· Contract extensions
Municipal strategies:
· Conservation required for all WUGs with shortages and per capita use above 140 gpcd
· Regional Water Management Strategies (refer to list above)
· Water transmission projects
· Off channel and channel reservoirs
· Recharge dams
Non-Rice Irrigation & Manufacturing strategies:
· Expansion of current groundwater supplies
· Transfers and allocations
· Temporary overdraft
Livestock & Mining strategies:
· Expansion of current groundwater supplies
· Development of new groundwater supplies
Rice Irrigation strategies:
· Continued use of Austin return flows
· Continued use of downstream return flows
· Water Management Plan – Interruptible water supply
· On-farm conservation
· Irrigation district conveyance improvements
· Conjunctive use of groundwater
· Development of new rice varieties
· Firm up ROR with off-channel reservoir
· HB 1437
· Supply reductions due to LSWP
· Transfer ROR supply to Municipal and Industrial
Steam-Electric Power strategies:
LCRA:
· Garwood water to Fayette Power Project
COA:
· Reuse (Direct and Indirect)
· Contract renewal
STP
· Brackish groundwater desalination
· Rainwater harvesting
The impacts associated with water management strategies were considered throughout the selection process, and strategies that imposed minimal impacts on the environment’s existing resources were weighted more favorably than less desirable strategies. The LCRWPG considered impacts to a number of resources, including:
· Water Quality
· Existing Water Rights
· Instream Flows
· Bay and Estuary Freshwater Inflows
· Sustainable Aquifer Yield
· Agricultural Water Resources
· Threatened and Endangered Species
· Wildlife Habitat
· Public Lands
By including alternative strategies in this plan, it was expressly recognized and agreed that participants in this planning process have not waived their right to raise legal arguments for or against those strategies or any applications either currently pending or that may be filed in the future. It was also expressly recognized and agreed that the disposition of strategies and alternatives that are affected by the uncertainties involved in pending litigation and contested-case hearings including as related to the applications listed in Chapter 2 of the draft plan, is not a basis for considering those alternatives to be inconsistent with the draft plan and the state water plan.
For the complete Lower Colorado Regional Water Planning Group’s Initially Prepared Plan refer to the TWDB website: http://www.twdb.state.tx.us/rwpg/main-docs/IPP-index.htm