This document summarizes the findings of a study evaluating rainfall-runoff trends in the Upper Colorado River Basin. The study found that while total annual rainfall has remained stable, there have been decreases in the duration of dry periods and increases in average temperatures. These changes have led to increases in evapotranspiration and reductions in streamflow, despite similar or higher rainfall amounts. Through modeling and analysis, the study attributed these trends to increases in small ponds and impoundments, changes in land use and land cover increasing surface runoff, and potential impacts to groundwater recharge. The results indicate the system is becoming more efficient at retaining rainfall rather than producing streamflow.

1. Got Streamflow?
Why More Rain
is Providing
Less Streamflow
in the Upper Colorado River Basin
TWCA Annual Conference
Fort Worth, TX
3/6/2020
Jordan Furnans, PhD, PE, PG
Vice President – TX Operations

2. Final Report: Evaluation of
Rainfall-Runoff Trends in the Upper
Colorado River Basin (Phase Two)
By LRE Water & Kennedy Resource Company
2018-2019
Project Funded Through TWDB Contract Number 1800012283
http://www.twdb.texas.gov/publications/reports/contracted_reports/doc/1800012283.pdf
** Part of Colorado-Lavaca BBASC Adaptive Management Program

3. Audience Challenge
WHAT DO WE DO WITH THIS INFORMATION?

4. BACKGROUND: From Comments to LCRA’s 2015 WMP – By Environmental Stewardship

5. Fate of Rainfall & Precipitation - Simplified
What Happens to Rainfall?
Evapotranspiration
Streamflow (Runoff)
Surface Storage
Soil Recharge

6. BACKGROUND: From Comments to LCRA’s 2015 WMP – By Environmental Stewardship

7. 2017 Study Phase-1: Objectives and Results
Objectives
1. Are recent observed flows in the Colorado River basin upstream of the Highland Lakes substantially lower
than historical flows?
2. If so, what are the likely reasons for the disparity?
Results
1. Observed flows declined at all study sites over the period 1940–2016.
2. Decline in a majority of the sites can be attributed to historical water use and the construction of large
reservoirs upstream (all permitted).
3. For several of the study sites, declines in flow were not the result of permitted upstream withdrawals.
4. All sites showed some decline in naturalized flow over the period of record.
5. Such a decline indicates that activities not accounted for in the flow naturalization process may have
impacted observed flows.
- e.g. construction of small reservoirs, groundwater use, changes in average temperature, etc.

8. Quick Summary of Phase 1 Results
“Rainfall in the 1950’s was similar to that in the recent drought – yet recent streamflow was much lower”
Ballinger, TX
RAINFALL (inches)
Elm Creek @
Ballinger, TX
Streamflow (1000 acre-ft)

9. Graphical Summary of Phase 1 Results – True for
all of Study Area
Similar Results – from multiple Study Sites
Conclusion:
Not so simple, depending
On analysis methods

10. Study Phase-1: RecommendationRecommendation:
1. Undertake a further study of potential factors affecting rainfall-runoff relationships within key
sub-watersheds
1. North Concho at Carlsbad
2. Elm Creek near Ballinger
3. South Concho
4. San Saba River watersheds
2. Derive definitive conclusions for the attribution of observed rainfall-runoff relationships.
Link to Phase-1 report: http://www.twdb.texas.gov/publications/reports/contracted_reports/doc/1600012011_Kennedy.pdf
Phase I Study Recommendations

11. Project Study Area – Phase II
Majority of study area in Region F
Results likely applicable to
Rest of Region F
Region G also interested:
Cedar Ridge Reservoir EIS
Region K has strong interest
LCRA

12. Precipitation Trend Analysis
Significant Decrease in length of dry periods

13. Precipitation Trends Ballinger, TX
Total Annual Rainfall: Stable
Dry Period Duration: Decreasing
# of Rainy Days: Increasing
Median Depth of Rain: Decreasing
January Stable 61.12%
February Increasing 94.13%
March Increasing 96.53%
April Decreasing 90.37%
May Stable 61.21%
June Increasing 95.43%
July Stable 6.23%
August Increasing 79.79%
September Stable 46.02%
October Stable 14.22%
November Stable 67.73%
December Stable 28.32%
Spring Stable 70.39%
Summer Increasing 99.23%
Fall Stable 30.54%
Winter Stable 44.42%
Annual Stable 70.50%

14. Temperature Trend Analysis – Ballinger, TX (Evapotranspiration Changes)
Ballinger TX – Extreme High Temperatures
– Decreasing or Stable
Ballinger TX – Minimum Temperatures
- Increasing
Ground is not cooling as much
as it used to!
Increase in Evapotranspiration
== Decreased Streamflow

15. Minimum
Temperatures
Maximum
Temperatures
Period Trend Confidence Trend Confidence
January Increasing 94.75% Stable 60.16%
February Increasing 92.50% Stable 47.28%
March Increasing 99.94% Stable 44.44%
April Stable 68.40% Stable 37.46%
May Increasing 94.76% Stable 67.33%
June Increasing 98.84% Stable 63.28%
July Increasing 96.38% Decreasing 76.75%
August Increasing 99.36% Stable 64.91%
September Increasing 96.85% Stable 6.31%
October Increasing 96.98% Stable 50.46%
November Increasing 99.83% Stable 69.01%
December Stable 70.09% Stable 39.79%
Spring Increasing 99.89% Stable 66.05%
Summer Increasing 99.51% Decreasing 88.85%
Fall Increasing 99.95% Stable 33.27%
Winter Increasing 95% Stable 21.33%
Annual Increasing 99.99% Stable 20.47%
Temperature Trend Analysis – Ballinger, TX (Evapotranspiration Changes)

16. Soil Moisture Data Analysis – NLDAS (Soil Recharge Changes)
Increase tied to Increasing Rainfall frequency w/ lower intensity?

17. NHD
2018 Image
Pond constructed
Between 10/2008 & 3/2010
Proliferation of Small Ponds in Watersheds – Storage Changes
2008 Image

18. Refining with Google Earth Engine: 1984-Present
Also Manual Review in Google Earth
Manual Review – USGS Topographic Maps
600 Additional Small Impoundments
Present in 2019 – Identified in Google Earth
Not Present in 2002 NHD
Small Impoundments:
• Water Loss to Evaporation
• Prevent runoff from reaching streams
**Volume estimated from WAM
storage vs area relationship
Lots of NRCS Dams
Proliferation of Small Ponds in Watersheds – Storage Changes

19. Groundwater Level Evaluations – Soil Recharge Changes ?
Apparent Linkage:
Groundwater levels : Streamflow : Rainfall
Lack of Groundwater level data from shallow wells
Groundwater pumping records
– spotty & unreliable
Texas law does NOT recognize a connection
between Groundwater and surface water

20. Baseflow Analyses of Streamflow
Separated Baseflow from Streamflow
using USGS techniques
Baseflow represents local groundwater
Contribution to streamflow
Baseflow remains stable
yet % flow as baseflow is increasing
Thus – Surface runoff is decreasing!

21. Land Use – Land Cover Changes – Curve Number Analysis
Standard SCS Curve Number Applications
100 = Impervious, More Runoff
30 = Pervious, Less Runoff

22. Demonstrating Cause and Effect
Upper Colorado Water Balance Model (UCWBM)
Uses Measured daily Rainfall
Applies SCS Curve Number Method to compute Q
Incorporates land use/land cover change
Accounts for small ponds:
• Storage prior to discharge downstream
• Evaporation loss from ponds
𝒒 =
𝑷 − 𝑰 𝒂
"
𝑷 − 𝑰 𝒂 + 𝑺
𝑰 𝒂 = 0.2𝑺
𝑺 =
1000
𝑪𝑵
− 10
Designed for comparing modeled Q
– not for matching measured Q
Elm Creek Watershed
Median 20% Decrease in Streamflow

23. Is this a local phenomena? Application for Kansas?
Rainfall & Temperatures near Council Grove, KS
1909-2018
Minimum
Temperatures
Maximum
Temperatures
Period Trend Confidence Trend Confidence
January Stable 69.36%Decreasing 76.78%
February Stable 23.58%Decreasing 80.21%
March Increasing 91.79%Stable 55.54%
April Stable 57.42%Decreasing 94.83%
May Increasing 96.49%Decreasing 94.26%
June Increasing 98.65%Decreasing 86.99%
July Increasing 99.86%Decreasing 99.05%
August Increasing 81.37%Decreasing 99.38%
September Stable 3.13%Decreasing 97.56%
October Decreasing 76.65%Decreasing 98.02%
November Stable 69.53%Decreasing 94.79%
December Stable 13.49%Stable 55.70%
Spring Increasing 96.50%Decreasing 91.88%
Summer Increasing 99.83%Decreasing 99.87%
Fall Stable 1.90%Decreasing 99.63%
Winter Decreasing 75.17%Decreasing 82.77%
Annual Stable 74.52%Decreasing 99.76%

24. FINAL THOUGHTS – FROM ENVIRONMENTAL STEWARDSHIP
Will low inflows cause more frequent
Curtailment of environmental flow releases
By LCRA?

25. QUESTIONS/DISCUSSION
Evaluation of Rainfall-Runoff Trends in the Upper Colorado River Basin
Phase II
March 6, 2020
Jordan Furnans, PhD, PE, PG
Jordan.Furnans@LREWater.com
(512) 736-6485
Final REPORT – Approved by TWDB October 11, 2019
Available Now:
http://www.twdb.texas.gov/publications/reports/contracted_reports/index.asp