So, let’s talk SCIENCE for a few minutes

Administrative Law Judges Rebecca S. Smith (right) and Ross Henderson (left).

As recently reported, the LCRA’s application for a groundwater permit is now in the hands of the Lost Pines GCD Board of Directors. Fortunately the Administrative Law Judges (ALJs) did not substantively alter their recommendation for the inclusion of a requirement for surface water monitoring, and the District has only limited ability to alter the recommendation of the ALJs. As such, the Proposal for Decision that has been sent to the Lost Pines Board still preserves Environmental Stewardship’s win regarding the need for monitor of surface water-groundwater interactions as a special condition in the permit. 

The following science discussion is provided to give a more visual understanding of what the ALJ’s saw and heard during the contested case hearing that caused them to recommend that surface water monitoring be required.


The Model Predicts Unreasonable Damage to the Colorado River by about 2050

The most important discussion relate to impacts of groundwater pumping on the Colorado River was the cross examination of the District’s expert witness on groundwater hydrology and groundwater modeling — Dr. William J. Hutchison — by our counselors Eric Allmon and Marisa Perales. 

Dr. Hutchison — who has had a distinguished career with Texas State Agencies — provided a report titled: Expert Report for the General Manager of the Lost Pines Groundwater Conservation District.  In producing the report Dr. Hutchison ran the updated Groundwater Availability Model (GAM) to produce the following graphic that demonstrates the impact of groundwater pumping on the Colorado River. (See Report – WILLIAM R. HUTCHISON pages 15-16 of the report and Figure 6 below with annotation by ES, click to enlarge.) 

Figure 6 from Dr. William J. Hutchison’s Report to Lost Pines GCD General Manager with annotation by ES

Figure 6 shows the surface water- groundwater interaction simulated by the revised GAM for river nodes located in the Colorado River Alluvium. The two pumping scenarios (red and purple) deviate in 2020 as a result of the start of LCRA’s proposed pumping. Here are the important conclusion from demonstrated by this figure:

  • During the pre-development period (1930-1990), the Colorado River gained water from the aquifers at a rate of about 60,000 acre-feet per year as it flowed through Bastrop County The calibration period for the model was 1930-2010. 
  • During the first phase of development (1990-2010), when ALCOA was dewatering a mining operation, the amount of water contributed to the river from the aquifers decreased to about 30,000 acre-feet per year. The two simulations (Base and Base + LCRA) start in 2020 and are simulated through 2070 (the joint planning period for Groundwater Management Area 12). 
  • The PURPLE line is “Base” pumping which includes the Districts’ best estimate of what will be pumped each year as a result of its currently permitted pumping. 
  • The RED line is “Base + LCRA” pumping. NOTE: If the LCRA is granted a permit for 25,000 acre-feet per year then the RED line becomes the new BASE. 
  • Dr. Hutchison’s graph estimates that the Colorado River will cease being a GAINING river (cease receiving an outflow from the aquifers) by about 2050 and will become a LOSING river (providing water to the aquifers) as it passes through Bastrop County.

LCRA’s groundwater hydrologist Steve Young and others characterized the reversal from a GAINING to a LOSING river as an UNREASONABLE effect of groundwater pumping on the Colorado River. 

Environmental Stewardship’s groundwater hydrologist George Rice conducted similar runs using the revised GAM and reported very similar results. 

A Model is a Model … and needs to be validated with field data. 

The revised GAM used to predict the impact of groundwater pumping on the river used field data to calibrate the model from 1920 through 2010. This was an important step in validating the model through that period. However, as the expert witnesses testified, the impact of high rates of groundwater pumping will likely cause the model to behave somewhat differently during the development years. As a result, there is a need to get good quality field data during the development period to validate that the model is giving predictions that are reliable enough to use as the basis for making regulatory decisions regarding future pumping.

The need for a surface water monitoring well network was demonstrated

Based on the evidence presented the ALJs agreed with Environmental Stewardship that there is a risk of unreasonable damage to the Colorado River and its tributaries AND there is a need to obtain field data to further validate the model. Further, they agreed that the LCRA must be required to design, install and operate such a surface water monitoring well system and that the requirement should be an enforceable special condition of the permit.


Environmental Stewardship’s legal team — Marisa Perales (center) and Eric Allmon (right) — cross-examining Lost Pines District’s hydrogeologist William Hutchison (left) on the impacts of LCRA’s pumping on the Colorado River.

The same hydrological effects of groundwater pumping impact tributaries of the Colorado River and exempt domestic wells

The hydrological effects that reduce outflows from the aquifers to the Colorado River also reduce outflows to its tributaries and lower water levels in domestic wells located in aquifer formation that are adjacent to the Simsboro formation.   Groundwater pumping in the Simsboro formation causes water to flow out of the Calvert Bluff, Hooper and to a lesser extent the Carrizo formation into the Simsboro formation.  This vertical flow lowers the water level in these formations affecting domestic water wells and outflows to Big Sandy, Wilbarger, Piney/Lake Bastrop and Cedar creeks.   

Marisa Perales and Steve Box consulting with expert witnesses George Rice (left) and Joe Trungale (2nd left)

Environmental Stewardship’s groundwater hydrologist George Rice took a slightly different approach to the modeling runs he conducted.  Whereas Dr. Hutchison lumped all outflows to surface waters together and counted them as one outflow to the Colorado River, Mr. Rice separated the outflows to the main stem of the Colorado from the outflows to tributaries.   As a result he was able to demonstrate that the tributaries will be impacted by groundwater pumping of the Simsboro formation in the same way as the main stem of the Colorado is impacted — by reversing the GAINING relationship to a LOSING relationship.   

The following graphs represent Mr. Rice’s findings when outflows from the aquifers are separated out for the Colorado River mainstream and the tributaries, Big Sandy, Wilbarger, Piney Creek/Lake Bastrop and Walnut/Cedar creeks: 

Impact of groundwater pumping on the main stem of the Colorado River predicting that it will become a LOSING river by 2040 with Baseline + LCRA pumping.

Impact of groundwater pumping on Big Sandy Creek predicting that it became a LOSING stream about 2015 with Baseline pumping.

Impact of groundwater pumping on Wilbarger Creek predicting that it will become a LOSING stream by about 2035 with Baseline plus LCRA pumping.








Impact of groundwater pumping on Piney Creek/Lake Bastrop predicting that it will become a LOSING stream by about 2025 with Baseline pumping


Impact of groundwater pumping on Walnut/Cedar Creeks predicting that they will become LOSING streams by about 2055 with Baseline plus LCRA pumping.
















In summary, the following conclusions can be drawn from this analysis:

  • The Colorado River is predicted to become a LOSING river as early as 2050 with Baseline + LCRA pumping.
  • Big Sandy Creek is predicted to have become a LOSING stream about 2015 with Baseline pumping only.
  • Wilbarger Creek is predicted to become a LOSING stream by about 2035 with Baseline plus LCRA pumping.
  • Walnut/Cedar Creeks are predicted  become LOSING streams by about 2055 with Baseline plus LCRA pumping.
  • Piney Creek/Lake Bastrop is predicted to become a LOSING stream by about 2025 with Baseline pumping only. 

NOTE:  The graphs above are from Environmental Stewardship’s motion to supplement the pre-filed testimony of its expert witnesses George Rice and Joe Trungale.  LCRA objected to the supplemental testimony and the ALJ’s did not allow this material to be made part of the record.  The same graphs — based on earlier GMA-12 pumping files — were a part of the prefiled testimony.  The above graphs have been annotated by Environmental Stewardship to show 1) the pre-Development (calibration) and the Development (pumping)  periods from 1930 to 2070 in Dr. Hutchison’s Figure 6, and 2) the point in time, as outflows from the aquifer into the river and tributaries decline, when the Colorado River, Big Sandy Creek, Wilbarger Creek, Waller/Cedar Creek, and Piney Creek go from being GAINING streams to LOSING streams as a result of groundwater pumping.

Clarification:  The incremental time step between data points on the Colorado River graph is 10 years, whereas the incremental time step between data point on the stream graphs is 30 years.   Thus the stream graphs appear as “straight line” graphs.  This is important when interpreting the period between 2010 and 2030 because LCRA pumping is not predicted to start until after 2020.  As a result, though it appears that Big Sandy and Piney Creeks become losing streams as a result of LCRA pumping, in reality the change to a LOSING stream is due only to Baseline pumping.  


Pumping the Simsboro formation of the Carrizo-Wilcox Aquifer Group results in drawdown of the Hooper, Calvert Bluff and Carrizo  formations and thereby directly impacts domestic well

There are important differences in the predictions of the old GAM and the new GAM.   Rice found that, in general, the old GAM predicted greater drawdowns in the Simsboro than the new GAM.  The new GAM predicts a water level decline in the Simsboro formation of 180 feet. The old GAM predicts a decline of 247 feet.

The new GAM also predicts that the proposed pumping of the Simsboro will cause an increase in drawdown in the adjacent formations at the proposed LCRA wellfield as follows:  In the Hooper formation, the predicted drawdowns are 22 feet (old GAM) and 37 feet (new GAM). In the Calvert Bluff formation, the predicted drawdowns are 20 feet (old GAM) and 45 feet (new GAM). In the Carrizo Aquifer, the predicted drawdowns are 1 foot (old GAM) and 6 feet (new GAM).

The predicted inflows (vertical leakage) to the Simsboro formation from the Hooper and Calvert Bluff formations would be expected to replace water that has been pumped out of the Simsboro formation with water from these formations thereby reducing the total measure drawdown in the Simsboro formation.  At the same time, the water leaked from the adjacent formations would cause these formations to show more drawdown.  Agreement with these expectations is a sign that predictions of the new GAM are reliable.  

In summary, the increased drawdown of the Hooper and Calvert Bluff formations have a direct impact on the quantity of groundwater available to outflow to surface water and the water level in domestic wells located in these formations.  As such, monitoring the drawdown in domestic wells and outflows to surface waters such as Big Sandy, Wilbarger, Piney and Cedar creeks are complementary predictors of the overall impacts of groundwater pumping on historical hydrological conditions in the Carrizo-Wilcox Aquifer Group.   

Surface water modeling predicts unreasonable impacts of groundwater pumping on surface waters of the Colorado River

Environmental Stewardship’s surface water expert witness, Joe Trungale, used the current surface water availability model (WAM) to evaluate the impact of reduced inflows to the Colorado River and its tributaries to predict changes in critical environmental flow attainment rates.  His testimony and overall conclusion are that:

  • Water in the Colorado River at Bastrop and below has, for all intents and purposes, been fully appropriated. A decrease in streamflows, including a decrease as a result of increased pumping of groundwater, would likely come at the expense of existing water rights holders, and these reduced flows would have an adverse effect on flows needed to maintain a sound ecological environment
      • The fact that this river is already over appropriated means that any reductions in flows will negatively impact existing water rights holders. Specifically, existing senior water rights holders will be able to divert less of the water that they are legally entitled to than they would be able to divert if there were no reductions in flow due to groundwater pumping. The WAM allows for a quantification of how many water rights holders would be negatively impacted.
      • There are about 1,300 active water rights in the Colorado basin though not all include authorization to divert water. The reliability decreases for almost every water right in the basin. It should be noted that the reduction in reliability was generally relatively small with less than a 3 percent reduction in reliability in almost all cases. However, the prior appropriation doctrine is intended to ensure that senior water rights are protected from new (junior) water development projects. New water development projects, generally, cannot be permitted if they would result in reducing the reliability of flows available to satisfy existing water rights, at the full appropriation amount permitted. Groundwater pumping appears to create a gradual reduction of reliable streamflows, over a relatively long period of time (versus an immediate reduction of streamflows from a single development project).
  • Environmental flow standards are not being met at recommended frequencies, and this permit would result in further reduction in these attainment frequencies. While there were some small changes in the results, the frequencies of meeting the flow standards are still below their recommended levels, and these shortfalls are further exacerbated by the decrease in flow as a result of the groundwater pumping. This reduction continues to be most concerning in the segments below Bastrop during spring when the base average flows, which are important for maintenance of habitat for the state-threatened Blue Sucker, drop further below already undesirable frequencies
  • The reduction in flows impacts the ecological health of the Colorado River.
      • A sound ecological environment is defined as “a functioning ecosystem characterized by intact, natural processes, resilience, and a balanced, integrated, and adaptive community of organisms comparable to that of the natural habitat of a region.” (Texas Instream Flow Program, Technical Overview, May 2008). Instream flow standards were recommended and adopted that included subsistence, base, high flow pulse, and bankful flows necessary to maintain a sound environment for the Colorado River.   These recommendations, consistent with literature on the science of instream flows recommended that flows be managed to mimic natural patterns. They further recommended that subsistence flows should be considered “hands off flows” with the goal that flows do not fall below the subsistence flow guidelines and thus should be met 100% of the time. For base flows, which provide for variable instream habitat conditions that differ during dry and average times, the recommendation was that base-dry and base-average flow magnitude occur 80 and 60 percent of the time.
      • These flow recommendations were adopted by the Senate Bill 3 Colorado Bay and Basin Expert Science Team and the Bay and Basin Stakeholder Advisory Group.
  • Table 1 (Exhibit 204) includes the results from my original simulations and those described in this supplement. As used in the table, GWP_ORG refers to simulations based on old GAM assumptions, GWP_SUP are based on new GAM and revisions to the analysis having to do primarily with the intermittency of tributary streams.

Table 1 Attainment Frequencies of SB3 Flow Standards in the Lower Colorado River

  • Permits for wells shall consider whether the proposed use of water unreasonably affects existing groundwater and surface water resources for existing permit holders.
      • I consider the effect of the proposed groundwater pumping on surface water resources to be unreasonable because it increases the shortfalls in meeting environmental flow targets. If the flows in the river are already below levels needed to maintain the ecological health of the river, then I  consider any additional pumping that causes further instream flow reduction to be unreasonable.
      • I did not see any analysis in the application that considered the effect of the proposed permits on existing (surface) water permit holders.
  • As a hydrologist, I understand that groundwater and surface water sources are physically connected and considering them as independent and disjointed is contrary to reality. The best available science concludes, logically, that pumping water from aquifers near the Colorado River and its tributaries will reduce the flow in the river and the tributaries.
      • Since this river is already fully appropriated, this reduction will adversely impact the reliability of water for existing senior water rights holders. The reduction in flow will also mean that the flows needed to maintain a sound environment, which in some cases are already not being meet,  would be further reduced below levels recommended by the best available science.
      • The uncertainty regarding the precise magnitude of the river flow decline does not change my fundamental conclusion. Groundwater pumping will decrease flows in the river and the tributaries, and or the reasons stated above, the river cannot afford the reduction.