Texas Water Conservation Association 71st Annual Convention
Pecos/Devils River Watershed Projects Part II
Ronald T. Green, Ph.D., P.G., F. Paul Bertetti, P.G., and Nathanial Toll
Geosciences and Engineering Division Southwest Research Institute®
Presented on behalf of the Irrigation Panel Page 1 Why is Preserving and Protecting the Devils River and Lower Pecos River Important?
Need to put
Pecos River these two rivers in a Devils River broader geographical context
Page 2 Rio Grande Watershed
Pecos River and Devils River play an integral role in the water resources of the Rio Grande
www.water.usgs.gov Page 3 Rio Grande Watershed
1/3 Of flow to the lower Rio Grande, 1/3 comes from NM 1/3 and CO, 1/3 comes from Mexico and mid- Texas, and 1/3 comes from Val 1/3 Verde County
www.water.usgs.gov Page 4 Rio Grande Watershed
Knowing these relative contributions is key to understanding their combined impact on the lower Rio Grande
www.water.usgs.gov Page 5 Rio Grande Watershed
There are agreements in place that dictate the terms Rio Grande Compact of agreement for the 1/3 from NM and CO and the 1/3 from Mexico, although each has issues Treaty of 1944
www.water.usgs.gov Page 6 Rio Grande Watershed
How the 1/3 from Val Verde County is managed is less settled…..
www.water.usgs.gov Page 7 How Much Water Are We Talking About? Average Annual Flow by Each River/Spring
Pecos River 197,000 acre-ft/yr Devils River 263,000 acre-ft/yr
Goodenough Springs San Felipe 103,000 65,000 acre-ft/yr acre-ft/yr
Page 8 Rio Grande Water Budget in Val Verde County (acre-ft/yr)
Pecos Devils River River Cienegas 263,000 197,000 Creek Goodenough 8,700 Spring 103,000 San Felipe Amistad Creek Reservoir 65,000 Rio Grande at Langtry 1,071,000 Rio Grande below Amistad Dam 1,659,000 Rio Grande at Del Rio Gauging Station 1,659,000
In an average year, 1.07 million acre-ft flows into Val Verde County and 1.7 million acre-ft flows out of Val Verde County via the Rio Grande Page 9 Amistad and Falcon Reservoirs Lose 100,000 acre-ft to Evaporation Every Year
Pecos River Devils Water demand in the lower Rio Grande River Cienegas Creek is 1,500,000 acre-ft/yr
San Felipe Amistad Creek Reservoir Rio Grande at Langtry 1,000,000 acre-ft/yr from surface water
Rio Grande below Amistad Dam 350,000 acre-ft/yr from groundwater
Gauging Station There was already a deficit of 150,000 acre/ft in 2010 in the lower Rio Grande
Falcon Reservoir An average of 100,000 acre-ft/yr of the flow in the lower Rio Grande is lost to evaporation regardless of river flow management * Lower Rio Grande Basin Study. Bureau of Reclamation & RGRWA Page 10 Studies are Underway to Better Characterize the Water Resources of the Lower Pecos River and Devils River Watersheds
Page 11 Related Studies Suggest There Is Limited Groundwater Flow from Adjacent Watersheds
Distinct Watersheds
Related studies of the Edwards Aquifer suggest watersheds on the edge of the Edwards Plateau act separately and there is limited groundwater flow between adjacent watersheds
Page 12 This suggests There Is Limited Groundwater Flow Between the Pecos, Devils, and Sycamore Watersheds
Water in each watershed will tend to stay in its watershed. It is unlikely that surface water or significant groundwater will flow from one watershed to an adjacent watershed, particularly where aquifers are shallow. Page 13 Lower Pecos River Watershed and Pecos River Watershed Should be Investigated Separately
Page 14 Pecos River Discharge
Pecos River discharge: 197,000 acre-ft/yr for 1967 -2009….
….but 32,000 acre-ft/yr for the period 1961-1967 during heavy pumping Ft Stockton and irrigation
Comanche Springs started to decline in 1947 and ceased flowing in 1961
Page 15 Lower Pecos River Watershed
Ft Stockton
Devils River Watershed Lower Pecos River Watershed
Page 16 How is this much water conveyed through this desert landscape?
Page 17 Consider the Presence of 1,000 gpm Wells Along Rivers in the Upper Devils River (Near Juno) River channel has lots of water…
…but, table lands are Where is this dry water coming from?
Page 18 Water Is Conveyed as Groundwater Upstream and Surface Water Downstream
Flow is as groundwater upstream where river beds are dry
…and as surface water downstream
Page 19 It is important to note that all high capacity wells in the Devils River watershed are located along major river channels
This observation is supported by a review of over 2,200 wells in the TWDB database
There are 752 wells with measured capacity in the TWDB database. When plotted on a map of the Devils River watershed, it is apparent that high capacity water wells are only located near river channels
Page 20 A Graph of These Data Support This Observation
Distance From River Channel Versus Well Capacity 3,000
) 2,500 Virtually all wells with capacity of 500 gpm
gpm are within 1.5 miles of a river 2,000
1,500
1,000
Well Pump Rate ( Well 500
0 0 2 4 6 8 10 12 14 16 Distance from Closest River Channel (mi) Page 21 The well data suggest there are preferential flow paths in the subsurface located near rivers that carry significant water.
If we consider the Edwards- Trinity Aquifer a sponge, then these preferential flow paths can be thought of as pipes in the sponge
Page 22 Step 1: The Edwards Plateau Was Formed by Sea Sediments that Solidified Then Lifted Over 10s of Millions of Years
Page 23 Step 2: River Basins Are Formed as the Edwards Plateau Is Uplifted and Rock Is Eroded
Once started, these river channels and basins probably retain the same alignment over millions of years Page 24 Step 3: Rain Water Is Focused into River Beds and Acts as a Mild Acid That Dissolves the Limestone
Incised River Channels
Preferential Flow Paths
The preferential flow paths that are formed may be a “pipe”, but it is more likely the flow paths are simply zones of enhanced permeability
Page 25 Two Important Points:
1)These preferential flow paths are in bed rock, not gravel beds
2) You cannot assume to have high capacity wells everywhere in Edwards-Trinity Aquifer just because you happen to have a high-capacity well that’s near a river channel
Page 26 Supporting Proof of Preferential Flow Channels in River Channels
Dye tracer tests in Sonora confirm the presence of preferential flow in Devils River channel
Groundwater will flow at most a few 10s of feet/yr in a porous media aquifer such as the Carrizo-Wilcox
Preliminary results from the Sonora tracer test suggests groundwater travels a half to one mile a day in the “pipes”
associated with Devils River Page 27 What is needed to build a model of the Devils River 1) Need to watershed? model the entire watershed
2) Need to add pipes
Page 28 How is Groundwater Flow Characterized by the Texas Groundwater Development Board?
Page 29 The Texas Water Development Board Model Appears To Be Based on the Mapped Geologic Formations
TWDB model of Mapped geology of Devils River watershed Devils River watershed hydrogeology
The Texas Water Development Board model units are represented as porous media (“sponges”) with no preferential flow paths Page 30 How Should the Devils River Watershed Be Modeled?
It is recommended the Refined characterization Devils River and Lower Of Devils River watershed Pecos River watersheds hydrogeology be modeled as separate hydrologic entities with preferential flow paths (i.e., “pipes”) embedded in porous media (i.e., “sponges”)
Page 31 Summary 3,000 2,500 2,000 1,500 1,000 500 Well Pump Rate (gpm) Rate Pump Well 0 • High capacity water wells are only located near 0 5 10 15 river channels Distance from Closest River Channel (mi)
• There are preferential flow paths in the subsurface located near rivers that carry significant groundwater
• Related studies suggest there is limited groundwater flow from adjacent watersheds
• Lower Pecos River and Devils River watersheds should be modeled as separate hydrologic entities
• Lower Rio Grande is dependent on management
of groundwater resources that supply 1/3 Amistad Reservoir 1/3
1/3 Page 32 Acknowledgements
Funding for water-resource assessment of Devils River Watershed provided by the Coypu Foundation
Funding for Devils River Groundwater Flow Model provided by the Nueces River Authority
Project support provided by the Devils River Conservancy
Page 33 Contact Information
Ronald T. Green, Ph.D., P.G. Institute Scientist Geosciences and Engineering Division Southwest Research Institute 6220 Culebra San Antonio, Texas 78238 1.210.522.5305 (office) 1.210.522.5184 (fax) 1.210.316.9242 (cell) [email protected]
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