1. Historical and Recent Characteristics of Freshwater Inflow and Salinity in the Laguna Madre and Rio Grande Estuaries
Caimee A. Schoenbaechler, Manager
Evan L. Turner, Ph.D., Coastal Scientist
Bays and Estuaries Program, Surface Water Division
Texas Water Development Board
May 24, 2017

2. Total Statewide Inflow ~40 million acre-feet/year
0.9
13.8
11.5
4.0
2.4
0.6
0.4
Average Annual Inflow
(million acre-feet per year; )
5.2
0.6
Total Statewide Inflow
~40 million acre-feet/year
The Texas coast is almost 400 miles long with numerous ecosystems and habitat types.
Along the coast, there are seven major (shown here in orange font) including the Sabine-Neches, Trinity-San Jacinto, Lavaca-Colorado, Guadalupe, Mission-Aransas, Nueces, and Laguna Madre Estuaries
and five minor estuaries (shown in blue font) including Christmas Bay, Brazos, San Bernard and Cedar Lakes, East Matagorda, and the Rio Grande
Together, these estuaries cover approximately 1.5 million acres.
These estuary ecosystems are largely shaped by an east to west precipitation gradient which drives a freshwater inflow gradient along the coast. On average, the Sabine estuary on the upper coast receives 14 million acre-feet of freshwater inflow per year and progressively decreases as you move down the coast to less than 1 million acre feet per year in the Lower Laguna Madre. On average, total statewide inflows are ~ 40 million acre-feet per year.
Top Left Photo: TWDB staff walking in Galveston Bay
Bottom Left Photo: Seagrass bed
Bottom Right Photo: Galveston Bay rainbow
texasseagrass.org

3. Coastal Hydrology Gaged Watershed Flows Ungaged Watershed Flows
Upper Laguna Madre & Baffin Bay
Lower Laguna Madre
Gaged Watershed Flows
+ Modeled (TxRR)
+ Return flows
- Diverted flows
Ungaged Watershed Flows
= Surface Inflows to Bay
Briefly, this is an overview of TWDB’s Coastal Hydrology program -- which estimates surface (freshwater) inflows to all of the major estuaries, as well as the Brazos River Estuary, San Bernard/Cedar Lakes Estuary, and East Matagorda Bay. The map above shows the coastal region of the Laguna Madre (Upper and Lower) Basin.
Freshwater inflow estimates are calculated based on four inputs: 1) USGS or IBWC stream flow gage data for watersheds with stream gages, 2) stream flow estimations of watersheds without stream gages using the TWDB Texas Rainfall Runoff model (TXRR), 3) TCEQ assembled list of self-reported stream flow diversions by water right holders, and 4) TCEQ and watermaster assembled list of self-reported stream flow returns (a.k.a. discharges) by water right holders.
Inflows are available as monthly or annual inflows from 1941 – 1976 for most estuaries. From 1977 to present, TWDB can provide daily, monthly or annual freshwater inflow estimates. However, the estimates are not real-time or even near real-time. For the Laguna Madre, prior to 1977 the estimates for Upper and Lower Laguna are combined. TWDB would need to recreate ungaged watershed estimates in order to develop independent datasets for each portion.
I invite you all to stay for the talk directly after this one in which my colleague Dr. Fernando will be giving a presentation on verifying and improving the Texas Rainfall Runoff model for simulating flow in ungaged subwatersheds draining to the Lower Laguna Madre.
USGS : San Fernando Alice
USGS : Los Olmos Creek near Falfurrias
IBWC
North Floodway near Sebastian
IBWC
Arroyo Colorado Floodway south of Harlingen
- Evaporation from the bay
+ Precipitation onto the bay
= Freshwater Inflow Balance

4. TWDB Estuary Monitoring Program
(The Datasonde Program)
Depth
Temperature
Salinity
Since the late 1980’s, TWDB has supported a coast-wide network of Datasondes, or water quality instruments, to measure salinity, temperature, and depth (and dissolved oxygen at some locations) along the Texas coast.
We partner with the Texas Parks and Wildlife Department to maintain this estuary monitoring program, who have sufficient field crews to make monthly site visits to service the instrumentation for data download and cleaning in between deployments.
Currently, this data is not real-time, but rather lags by about six months.
We use this data for monitoring bay conditions and to calibrate and validate our hydrodynamic and salinity transport models. Many coastal researchers across the state depend on this data for their own studies of bay ecosystems and was essential during the Senate Bill 3 process to establish freshwater inflow standards for the major estuaries.
This slide shows the 16 active long-term monitoring stations supported by TWDB as well as an example of the time-series data plotted up at the Realitos Peninsula station in the Lower Laguna Madre.

5. New Coastal Data on Water Data for Texas!
The Texas Water Development Board has recently launched the Water Data for Texas website, which is an ongoing effort to synthesize and communicate water-related data to scientist, policymakers, and the public.
As part of this effort, we recently published Coastal data on this website. The website allows customers to visualize and download the data that we collect at continuously monitored locations as part of the Datasonde Program, as well as point measurements collected by the Texas Parks and Wildlife Department’s Coastal Fisheries Program. It also now includes the freshwater inflow estimates developed by the coastal hydrology program.
Data and information on reservoirs, drought, and groundwater are also included on this webpage.
This project was made possible by a Coastal Impact Assistance Program grant via the Texas General Land Office.

6. Laguna Madre TxBLEND Model
TxBLEND Model Description
2-D, Vertically-Averaged
Finite Element
Unstructured Grid
Bathymetry
Time-Varying Boundary Conditions
River Inflow
Tidal Elevation
Wind Speed & Direction
Evaporation & Precipitation
Salinity
Model Output
Water Surface Elevation
X- & Y- Velocity
TWDB’s hydrodynamic and salinity transport model is the TxBLEND model which allows for modeling scenarios of changing inflows, climate, or physical geometry to predict effects on salinity and circulation patterns within the bay. It has been in use for several decades, and calibrated models exist for all of the major Texas bays. It has most recently has been used widely by participants in the Texas Senate Bill 3 process to develop environmental flows. And, while it certainly has limitations in terms of performance and resolution of salinity at smaller scales – it has been good at providing a broad bay-wide view of salinity responses over multi-year simulations. In addition, it is computationally fast – even for these multi-year simulations.
TxBLEND is a 2-D, depth-averaged model that provides output for Salinity, Water Surface Elevation, the x- and y- components of Velocity. It relies on model inputs for river inflow, tidal elevation, wind, as well as evaporation/precipitation on the bay. Off-shore measures of salinity are used to set the initial Gulf boundary condition. In addition to the Laguna Madre system, the model grid also represents Copano, Aransas, and Corpus Christi bays to the northeast. These bays are included to yield better simulation results by modeling conditions at the boundary of the estuary. Inflow points to the Lower Laguna Madre include the Main Floodway, the North Floodway (Arroyo Colorado) and San Martin.
The calibrated and validated model is available for 1995 – 2010.
TxBLEND does not include a turbulence closure model, temperature transport, or wetting and drying.
10 TxBLEND inflow points: LLM inflow points include: San Martin, Arroyo Colorado, Main Floodway
Schoenbaechler, C., C.G. Guthrie, J. Matsumoto, and Q. Lu TxBLEND Model Calibration and Validation for the Laguna Madre Estuary. October 27, 2011.

7. Data Recovery Efforts: Improving access to historical data
2005
1985
There has been growing interest from stakeholders to extend our hydrodynamic and salinity transport modeling capabilities backward in time to include the drought of the 1950’s to visualize bay salinity changes as a function of changes in hydrology and bathymetry over time. In order to successfully accomplish such a task, datasets used as inputs to drive the model have to be obtained, as well as datasets used to validate model performance.
We conducted an exploratory exercise for the Galveston Bay system at the request of the National Wildlife Foundation. At the time of that study, our most recent calibrated & validated model for Galveston Bay covered the time period from 1987 – Therefore, our efforts focused on developing data sets, model grid, and model parameters to extend the model backwards from and forward to in order to simulate salinity for the full period of interest.
We found that we could obtain the necessary datasets (hydrology, tide, wind, precipitation, and evaporation) to run the model but salinity data available however was much less certain. We needed off-shore/gulf salinities to drive the Gulf Boundary condition of the model as well as in-bay salinities for model validation.
Fortunately, the Galveston Bay system has been studied for a long period of time and so we were able to find thousands of historical salinity data points. This information came largely from three main sources including the Texas Parks & Wildlife Department historic reports, a Galveston Bay Estuary Program data archiving study, and TWDB-collected data.
The importance of long-term datasets is critical to understanding long-term trends and testing ecological theories, as well as developing management practices based on sound ecological science.
To conduct similar efforts for rother bay systems would first require obtaining historical datasets.
My colleague, Dr. Turner, will now describe to you his data recovery efforts to better understand historical and recent trends in freshwater inflow and salinity in the Laguna Madre and Rio Grande estuaries.

8. Comparing the 2010’s to the Historical Record
Is the Laguna Madre experiencing a ‘wet’ period?
1979
1983
2004
2012
1994

9. Methods: Historical Studies
Segment No Laguna Madre, WQS-14, Texas Department of Water Resources
Laguna Madre Estuary: A Study of the Influence of Freshwater Inflows, LP-182, Texas Department of Water Resources. Feb
Hard to make “apples to apples” comparisons
Stations moved over time (and, pre-GPS)
Time between samplings different
Do not have access to raw samples

10. Salinity (ppt)
Laguna Madre Estuary: A Study of the Influence of Freshwater Inflows, LP-182, Texas Department of Water Resources. Feb

11. Beulah (1967)
Fern (1971)
Salinity (ppt)

12. Methods: Current Observation Stations
In-Situ YSI sonde instruments maintained by Texas Parks and Wildlife Department
Hourly time series downloaded monthly
LMA2 09/ Current
SPCG 01/2011 – Current
REAL 01/2011 – 05/2014
LMA2
REAL
SPCG

13. Alex (2010)
TS Don (2011)
Ingrid (2013)
TS Dolly (2014)
Patricia (2015)
Newton (2016)
Salinity (psu)

14. Comparison of Lower Laguna Madre (2010-2016) to Historical Record (1941-1976)
Salinity (psu)/(ppt)

15. Laguna Madre – Cumulative Annual Inflow
Alex (2010) TD #2 (2010)
Acre-feet
Annual Average Inflow
Lower_LM 529,952
Upper_LM 336,675

16. Conclusions
Large, infrequent storms are the main driver of inflow and salinity for the region.
The 2010’s have been exceptionally ‘wet’ for the Laguna Madre compared to the historical records.
Increased storm activity this decade has significantly impacted the salinity record.
TWDB continues to support data collection and studies in the Lower Rio Grande Valley to further understand inflow needs of the Lower Laguna Madre and Rio Grande Estuary.
TWDB continues to support data collection and studies in the Lower Rio Grande Valley to further understand inflow needs of the Lower Laguna Madre and Rio Grande Estuary.

17. Thank You! Bays & Estuaries Program Staff:
Caimee A. Schoenbaechler, Manager Evan L. Turner, Ph.D., Coastal Scientist
D. Nelun Fernando, Ph.D., Hydrologist
Dale Crockett, Hydrologist
Taylor Sansom, Coastal Modeler

18. Bonus Study Intensive Inflow Study of 1980
Hourly observation for 75 hours at 14 stations across entire Laguna Madre!
Current flow & Tide
Salinity/Temperature/Dissolved Oxygen
Water Chemistry
Bathymetry cross sample
Dye Tracing

21. Study spanned > 100 miles
Multiple shift crews, relief boats and trucks
Crews slept on station taking shifts

22. Thank You! Bays & Estuaries Program Staff
Caimee A. Schoenbaechler, Manager Evan L. Turner, Ph.D., Coastal Scientist
D. Nelun Fernando, Ph.D., Hydrologist
Dale Crockett, Hydrologist
Taylor Sansom, Coastal Modeler

23. Senate Bill 3 - Laguna Madre Freshwater Inflow Recommendations
Analysis of Natural Flows versus Modern Day Flows
Modern flows are elevated relative to natural flows
Dry season (Oct – Mar) inflows are very elevated
Under low inflow conditions, Natural flows were 11% to 40% of modern flows
Under high inflow conditions, Natural flows were 50% to 97% of modern flows
BBEST Recommendation
A sound ecological environment in the LLM needs less freshwater inflow and reduced nutrient loading.
Wet season inflows should not exceed 38,152 a-f/month to protect seagrasses
Dry season inflows should range 3,613 to 12,901 acre-feet per month (corresponding to the 25th to 75th percentile of natural flow conditions).
Recommends exploring strategies to reduce return flows , nutrient loading, and NPS pollution
An analysis of natural flow conditions relative to current conditions (monthly flows) – conducted by the Texas Water Resource Institute for the BBEST – showed that modern-day inflows are elevated relative to natural flow conditions, particularly during the dry season (Oct - Mar).
- Natural flows = flows w/o municipal and agricultural return flows (see BBEST Ch. 2.6)
Under Lower Inflow conditions, natural inflows were estimated to be 11% to 40% of the flows that occur today. (Much less than half of what we see today in the system) Under Higher Inflow conditions, natural flows were estimated to be 50% - 87% of modern day flows (at least half of today’s flows with the highest flows during modern-day wet seasons being reasonably similar to natural conditions).
BBEST Recommendations
Generally reduce flows and reduce nutrients
- Not enough data/information to develop a specific freshwater inflow regime recommendation.
- Wet season flows should range 7,888 to 38,152 acre-feet per month during at least three months and not exceed 38,152 af/month.
- Dry season flows should range 3,613 and 12,901 acre-feet per month during at least three months.
These values correspond to the 25th to 75th percentile of natural flows.
NOTE: For dry season flows, the maximum recommendation of 12,901 a-f/m corresponds to the minimum inflow recorded in modern day!!
(wet season flows range from below the current minimum to ~50th percentile flows)
Rio Grande BBEST Environmental Flows Recommendations Report . Final Submission to the Environmental Flows Advisory Group, Rio Grande Estuary and Lower Laguna Madre Basin and Bay Area Stakeholders Committee, and Texas Commission on Environmental Quality by the Rio Grande, Rio Grande Estuary, and Lower Laguna Madre Basin and Bay Expert Science Team. July 2012.