Applying%20TxRR%20to%20Texas%20Coastal%20Basins

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Applying TxRR to Texas Coastal Basins

• Victoria Samuels
• CE 394K.2

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Background
Three state agencies have been assigned the
cooperative task of determining just how much
water will be needed to maintain our state's
streams, rivers, Bays Estuaries. Currently, the
Texas Water Development Board is working with the
Texas Parks and Wildlife Department and the Texas
Natural Resource Conservation Commission (TNRCC)
to collect data and conduct studies on the needs
for instream flows and freshwater inflows to the
estuarine systems. http//hyper20.twdb.stat
e.tx.us/data/bays_estuaries/bepage.html
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TxRR development

• Estimates runoffs from ungaged watersheds
• Estimates streamflows on a daily basis
• Analyzes soil moisture continuously
• Analyzes direct runoffs by event

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TxRR framework

• Agricultural Research Service (ARS)
• 12 monthly depletion factors rather than 1 annual
  factor (used in soil moisture)
• Soil Conservation Service (SCS) Curve Number
  Method
• Parameter Optimization using Newtons Method
• Changed to Genetic Algorithm
• SCS Unit Hydrograph
• Changed to Gamma function (GAMMADIST function in
  Excel)

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TxRR Water Balance
Precipitation P
Initial Abstraction Ia
Direct Runoff QD
Infiltration F
Maximum Soil Moisture SMMAX Soil Moisture SM
Soil Retention S
Stream Flow
Base Flow QB
Percolation (not modelled)
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How Soil Moisture works - Time
Precipitation Event i-1
Precipitation Event i
Precipitation Event i1
In i-1 time
SM2 SM1
Time between Precipitation Events ti
In i time
SM2 SM1
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Sequence of Model

• Before Precipitation Event i
• Soil Moisture depleted from end of event i-1 to
  before event i
• Soil Retention increases
• It Rains! Pi at ti
• Initial abstractions subtracted
• Runoff produced
• Excess goes to Infiltration

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Soil Moisture Depletion
SM2i SM1i-1 exp (-amti)
SM2i soil moisture right before i
precipitation SM1i-1 soil moisture right after
i-1 precipitation am monthly depletion factor for
month m ti arrival time in days of the i
precipitation

• Monthly depletion factors
• Arrival time of precipitation events

INPUT
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Soil Retention
Si SMMAX SM2i
SMMAX the maximum soil moisture SM2i soil
moisture right before i precipitation Si soil
retention at the beginning of i precipitation
Soil Retention is the dry space in the soil
column, the room available for additional
moisture or an abstraction.

• SMMAX optimized in model

INPUT
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Direct Runoff
QDi Pei2 / (Pei Si) Pei Pi Iai Iai
abst1 Si
QDi direct runoff from i precipitation Pei effecti
ve precipitation Iai initial abstraction from i
precipitation abst1 initial abstraction
coefficient (usually 0.2)
Essentially the SCS Direct Runoff Equation

• Pi precipitation from i event
• abst1, user defined

INPUT
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New Soil Moisture
SM1i SM2i Fi Fi Pi Iai - QDi
SM1i new soil moisture right after i
precipitation Fi infiltration after i
precipitation
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Coming Soon

• Baseflow Calculations modelled with Soil
  moisture conditions
• Daily Streamflow Simulation
• Applying the Model

Acknowledgements Barney Austin, Dr. Maidment,
Richard Gu, Jerry Perales