Guadalupe River Chapter
of Trout Unlimited

About

Join

Volunteer

TU

Contact

Links

Flows

Forums

Photos

Ads

News

Home

What Determines the Minimum Flow on the Guadalupe?

The GRTU-GBRA Contractual Trout Protective Flow

First, and most significant, are minimum flows designed to protect the trout fishery in 10 milesbelow Canyon Dam. In 2001, GRTU and GBRA arrived at a settlement of the 1999 GBRA Canyon Lake Water Right Permit where GRTU contested the permit. The permit increased GBRA's water rights to Canyon Lake by an additional 40,000 acre feet, but to gain the water, the natural flow of the river had to be legally captured in the lake and not passed through the dam. This would have reduced the flows to the trout fishery. The settlement granted the following trout protective flows: "GBRA agrees that the minimum daily release from Canyon Reservoir for each day during the months of May, June, July, August and September of each calendar year during the term of this Contract will be not less than the release specified below for that day (averaged over 24 hours), if and only if Canyon Reservoir reaches an elevation greater than 909.0 feet m.s.l. for any length of time prior to that day during the period between January 1 and September 30 of that year:"

The FERC Minimum Flow Requirement

Beyond the Contract, the first regulatory requirement for minimum flows came from theFederal Energy Regulatory Commission (FERC) Requirement. This requirement is the result of theGBRA operated hydro-electric plant at the base of Canyon Dam. Article 405 states: The licensee shall discharge from the Canyon Dam Project a continuous minimum flow of 90 cubic feet per second, as measured immediately downstream from the project powerhouse to protect and to enhance fish and wildlife resources In the Guadalupe River. The flow may also be reduced to not less than the Inflow to the reservoir during periods of drought. For the purposes of this article, a "drought" begins the day after any period of forty five (45) consecutive days during which the inflow to Canyon Reservoir averages less than 90 (cfs), and shall continue until the reservoir level returns to 909 feet above mean sea level. Additionally, at times other than during periods of drought when the inflow to the reservoir is greater than 90 cfs, the licensee shall, at a minimum, discharge from the project whichever is least (a) the inflow to the reservoir or (b) a continuous minimum flow in accordance with the following schedule:

The Texas Commission on Environmental Quality Requirement

If you thought thinges were complicated, the TCEQ set up their own formulas for minimumflows below Canyon Dam. This was done in conjunction with the 1999 GBRA water permit that grantedGBRA additional water rights to Canyon Reservoir. The original 1956 water permit granted GBRA50,000 acre feet per year. With the 1999 permit, they were granted an additional 40,000 acre feetper year for a total of 90,000 acre feet. To manage two permits within one reservoir requiresa complicated computer program that divides one 'physical' reservoir into two 'virtual' reservoirs. The TCEQ mandated minimum flows are contingent on the "Base Storage Level" of CanyonReservoir being above 909.0 msl on any day on, or after, January 1 of the calendar year. Itends when the "Base Storage Level" is below 909.0 and inflows to Canyon Reservoir averageless than 90 cfs during any period of 45 consecutive days. The Base Storage Level is a 'virtual'measurement and cannot be determined by phyiscal gage, but by GBRA's spreadsheet.

The TCEQ minimum flow from Canyon Dam is a "pass-thru" requirement. That means flows into CanyonLake (as measured at the Spring Branch Gage) must at least be as great as the following:

In addition to the "Pass Through" requirement, there is a "Diversion" requirement that couldalso impact the release from Canyon Dam. "Water may be diverted from the Guadalupe Riverat any point downstream of it confluence with the Comal River and upstream of the U.S.G.S. Gaging Station at Gonzales, Texas to the extent such diversions do not reduce the measured streamflow at Gonzales below the specified amounts:

If the diversions reduce the flow at the Gonzalez Gage below the above rates, then an additionalflow (see the monthly flow values from the Pass Through table) must be allowed to remain in the river to the "salt water barrier".

GBRA-Comal County Contract For Recreational Flow

Comal County arrived at a contract with GBRA in which GBRA agreed to request a deviation in theCorps of Engineers flood control release procedures from Canyon Lake. The lake is in flood whenever the elevation exceeds 909.0 msl. On a year by year basis, the request must be made to the Corps.The deviation allows the lake between 909 and 910 to have a "recreational pool" where the floodwaters are released at a minimum of 250 cfs, or higher, depending on the inflow to Canyon Lake.The deviation is generally in effect from April through August.The two wettest months are May and June, so this provides additional protection to the trout fishery.

GBRA Selling Water to a Downstream Buyer

One of the primary purposes of GBRA is to act as a water supplier. With the additional amountsof water GBRA is allowed to store in Canyon Reservoir, there is the potential for more waterto be sold. Up to this point in time, little use has been made of the water supply function ofCanyon Lake. However, with the future demand increasing, more water is available to be soldand a lot of that will be to satisfy demand downstream.

Texas Water Law Requirements

Last, but not least, water rights must be passed through Canyon Lake for more senior waterpermit holders. In Texas, first, in time is first in right. So if a water right exceeds the 1956 or 1999 permit dates to Canyon Lake, any water flowing into Canyon Reservoir must be "passed through" the reservoir and to the more senior permit. These flow amounts are generallyinsignificant.