May 22, 2019

Estimating and Evaluating Spillway Capacities of Guadalupe Valley Hydroelectric System

Dams on Guadalupe River, TexasCleveland, Ohio

Prepared by:Max ShihSamuel PlazaRachel Sebian

SCOPE OF WORK

Scope of Work

Develop reservoir elevation-discharge relationships for Guadalupe-Blanco River Authority (GBRA) Dams: 1. Lake McQueeney Dam (Dam ID: TX01601) 2. Lake Placid Dam (Dam ID: TX01600) 3. Lake Meadow (Nolte) Dam (Dam ID: TX01599) 4. Lake Gonzales Dam (Dam ID: TX01912) 5. Lake Wood Dam (Dam ID: TX01913) 6. Lake Dunlap Dam (Dam ID: TX01606)

These dams were built in 1930s. Refine and update the dam discharge rating curves using the

recent engineering computer program (HEC-RAS 5.0).

3

Dam Locations

Guadalupe River

4

Run-of-the-River Dams

5

Primary Purposes

Hydroelectric

Water Recreation

6

7

Crest Gates of a GBRA Dam

8

ENGINEERING APPROACH

10

Engineering Approach

• During major flood events– The crest gates are total opened/flatted during the major flood

events.– The hydropower turbine is shut down.

• One dimensional HEC-RAS Steady Flow Model.– Given USACE Unsteady HEC-RAS model (2017)– Revised frequency flood discharges (2019)

• Calibrate the models to the available flood records (observed, water marks, time series data, etc.)

• Elevation-Discharge-Weir Coefficient relationships

11

Best Available Data

• Original Dam As-Built Drawings (1926-1931) for these six dams.

• Dam Survey, 2010, Surveying and Mapping, LLC (SAM).• TNRIS 2012 50cm TCEQ Dam Safety Sites LiDAR• TNRIS 2013 50cm Ellis, Navarro, Wilson, Karnes LiDAR• 2018 Bathymetric Data (Limited) • Preliminary Guadalupe HEC-HMS Model results dated on

December 19, 2018.•

12

Modeled Cross Sections of a Dam

Riverine Hydraulics

Modify On-going FIS HEC-RAS model

14

Downstream Boundary Conditions

USACE, 2017

Model Calibration

Model Calibration

Historical Flood Events (1972, 1998, 2002, 2010) Manning n values, ineffective flow area,

contraction/expansion coefficients

16

Calibration

17

Updated Frequency Flood Discharges

Updated hydrology with NOAA Atlas 14 rainfalls.

NOAA Atlas 14 Vol 11 (2018): Precipitation-Frequency Atlas of the United States, Texas

A 25% to 35% increase in the 1% (100-year) discharges

18

Dam Peak Discharge (cfs)*

1% (100-Year) 0.2% (500-Year) Lake McQueeney Dam 109,857 175,020

Lake Placid Dam 114,507 183,740

Lake Meadow (Nolte) Dam 111,036 179,708

Lake Gonzales Dam 156,830 273,196

Lake Wood Dam 149,610 273,249

Lake Dunlap Dam 110,012 170,891

Additional Result Evaluation – Weir Coefficients

19

20

Findings & Limitations

• No gaged flood events with a water level above dam crest.

21

Findings & Limitations

Spillway CapacityReturn Period in Year

Lake McQueeney Dam 100Lake Placid Dam

Existing Dam Conditions

Lake Wood Dam

23

Dunlap Dam (May 14, 2019)

24

25

• The spillway capacity is about the 25-yr flood. • Discharge was gradually increased from about 1000 cfs to

1900 cfs before dam failure. • This a run-of-river dam failure under fair weather conditions

Daily Discharges (May 13 - May 16, 2019)

Questions

Estimating and Evaluating Spillway Capacities of Guadalupe Valley Hydroelectric System Dams on Guadalupe River, TexasSCOPE OF WORKScope of WorkDam LocationsRun-of-the-River DamsPrimary PurposesRun-of-the-River Dams (GBRA)Crest Gates of a GBRA DamENGINEERING APPROACHEngineering ApproachBest Available DataModeled Cross Sections of a DamRiverine HydraulicsDownstream Boundary ConditionsModel CalibrationModel CalibrationCalibrationUpdated Frequency Flood Discharges Additional Result Evaluation – Weir CoefficientsFindings & LimitationsFindings & LimitationsExisting Dam ConditionsLake Wood DamDunlap Dam (May 14, 2019)Daily Discharges (May 13 - May 16, 2019)Questions