- What is the current Agreed Order for the Choke Canyon / Lake Corpus Christi Reservoir System with respect to freshwater inflows into the Nueces Estuary?
The City of Corpus Christi is required to allow fresh water to “pass through” the reservoir system to the Nueces Estuary each month. The monthly passthru requirement, or target, is dependent on several variables:
- Measured inflow into the reservoir system
- Percent capacity of the reservoir system
- Month of the year
- Salinity level in Nueces Bay
Paraphrasing the operating order: “Inflow into the reservoir system, up to the monthly target, must be passed through to the Nueces Estuary. Inflow exceeding the monthly target can be captured for future use. No release of stored water is required to meet the target amount.”
|Passthru Targets (AcFt)|
|Month||Capacity >= 70%||40% <= Capacity < 70%||30% <= Capacity < 40%||Capacity < 30%|
- How is the inflow into the reservoir system measured?
The City of Corpus Christi uses flow data from five streamflow gauges maintained by the US Geological Service to compute the daily inflow. The gauges used are:
- FRTT: Frio River at Tilden, Texas
- SMTT: San Miguel Creek at Tilden, Texas
- NTRT: Nueces River at Three Rivers, Texas
- NRTT: Nueces River at Tilden, Texas
- ARWT: Atascosa River at Whitsett, Texas
Using the acronym of the gauge to represent the flow at that gauge, the inflow is computed as:
(FRTT + SMTT + NTRT) – Release from Choke Canyon.
In the event that more water is being released from Choke Canyon Reservoir than is flowing into the reservoir system, the inflow is computed as: NRTT + FRTT + SMTT + ARWT.
The normal release from Choke Canyon Reservoir is 29cfs (58 AcFt) to meet downstream water rights and maintain flow in the Frio River below the dam. Exceptions occur during flood events and during times of drought to maintain the level of Lake Corpus Christi.
- What is the current freshwater inflow requirement to the Nueces Estuary?
The City of Corpus Christi posts the “Choke Canyon / Lake Corpus Christi Reservoir Daily Pass-Thru Status Report” every day. The current freshwater inflow requirement is shown as the “Target Passthru” under the “Estuary Inflows and Passthru Requirements” section.
- Where can I get information on past freshwater inflow requirements to the Nueces Estuary?
The Nueces River Authority (NRA) hosts the “Choke Canyon / Lake Corpus Christi Reservoir Daily Pass-Thru Status Report“. This page includes access to historical reports going back to January 1, 2000.
- Where is the freshwater inflow into the Nueces Estuary measured?
The USGS maintains a stream flow gauge, Nueces River at Calallen, Texas (NCAT), that measures the flow past the Salt Water Barrier Dam and therefore into the Nueces Estuary. The gauge is located off IH-37 upstream of where the river flows under the highway. Water is also pumped directly to the upper Nueces Delta via the Rincon Bayou Pump Station and Pipeline and counted towards the inflow amount.
- What is the difference between a “release,” a “passthru,” and a “spill”?
Many people use the word “release” when referring to releases, passthrus, and spills. The word RELEASE refers to stored water that is let out of a lake to meet downstream water rights and supply raw water to water treatment plants. The word PASSTHRU refers to the water that has flowed into the reservoir system, up to the monthly target amount, and is let out of Lake Corpus Christi to meet the freshwater inflow requirements to the Nueces Estuary. The word SPILL refers to the water that is released from the lake because the lake is full and can not hold any more.
- What is the current salinity level in Nueces Bay?
The Division of Nearshore Research of Conrad Blucher Institute of Surveying and Science (CBI) at Texas A&M University-Corpus Christi maintains the salinity monitoring station (SALT03) and posts a Salinity Relief Check page that is updated daily. CBI maintains other stations as well, but SALT03 is the one that is used for determining the salinity in Nueces Bay with respect to the Agreed Order.
- Where can I get information on past salinity levels in Nueces Bay?
The address for the Salinity Relief Check page is http://lighthouse.tamucc.edu/salrel. Historic information can be obtained by adding the desired month and year to the address. For example, the page for July 2001 is http://lighthouse.tamucc.edu/salrel/07.2001
- What credits can the City of Corpus Christi receive towards the monthly freshwater inflow requirement?
The City of Corpus Christi receives 500 AcFt per month return flow credit for all return flows into Nueces Bay, including the Allison Wastewater Treatment Plant, and possibly ONE of the following:
- Up to half of the monthly target from flows exceeding the freshwater inflow requirement in the previous month.
- The Salinity Relief credit when the salinity in Nueces Bay is low.
- How does the City of Corpus Christi receive salinity relief credit towards the freshwater inflow requirement?
The salinity relief credit is a reduction in the passthru target amount that can be obtained in a couple of ways.
- In any given month, if the average salinity during the week of the 15th through the 21st, is at or below the Salinity Lower Bounds (SLB) for the following month, then the target amount for the following month will be completely suspended.
- In any given month, if the average daily salinity is X practical salinity units (psu) below the Salinity Upper Bounds (SUB) for 10 consecutive days, then the target is reduced by Y% (See table below).
MONTHS Salinity Lower Bounds Salinity Upper Bounds Reduction for Average Salinity 5 psu below SUB 10 psu below SUB 15 psu below SUB Jan 5 30 25% 50% 75% Feb 5 30 25% 50% 75% Mar 5 30 25% 50% 75% Apr 5 30 25% 50% 75% May 1 20 0% 25% 75% Jun 1 20 0% 25% 75% Jul 2 25 25% 50% 75% Aug 2 25 25% 50% 75% Sep 5 20 0% 25% 75% Oct 5 30 0% 25% 75% Nov 5 30 25% 50% 75% Dec 5 30 25% 50% 75%
- What are the current lake levels and percent of capacity?
The current lake elevations and percent of capacity are shown under the “Reservoir Statistics” section of the “Choke Canyon / Lake Corpus Christi Reservoir Daily Pass-Thru Status Report“. This information is also displayed on NRA’s Home Page.
- Where can I get information on historic lake levels?
The Nueces River Authority maintains a web page with current and historical elevation, volume, and percent of capcity information. There is also monthly information on rainfall, inflows, required passthrus, and water from the Lake Texana via the Mary Rhodes Pipeline.
- Where can I get stream flow information?
The U.S. Geological Survey maintains stream flow gauges throughout the state of Texas. Here’s a link to the gauges in the Nueces River Basin.
- Where can I get river flood forecasts?
The National Weather Service maintains this type of information.
- Where can I get a summary of water use?
The Nueces River Authority maintains a web page providing monthly summaries of water supply information pertaining to the Choke Canyon/Lake Corpus Christi Reservoir System and the Mary Rhodes Pipeline.
Note: This information is available from January 2001 to present.