Applying TxRR to Texas Coastal Basins Victoria Samuels CE 394K.2

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.state.tx.us/data/bays_estuaries/b&epage.html

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

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 Newton’s Method Changed to Genetic Algorithm SCS Unit Hydrograph Changed to Gamma function (GAMMADIST function in Excel)

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)

How Soil Moisture works - Time Precipitation Event “i-1” Precipitation Event “i” Precipitation Event “i+1” In “i-1” time: SM2 SM1 Time between Precipitation Events = ti In “i” time: SM2 SM1

Sequence of Model Before Precipitation Event “i” It Rains! Pi at ti 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

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:

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. INPUT: SMMAX optimized in model

Direct Runoff QDi = Pei2 / (Pei + Si) Pei = Pi – Iai Iai = abst1 * Si QDi direct runoff from i precipitation Pei effective 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:

New Soil Moisture SM1i = SM2i + Fi Fi = Pi – Iai - QDi SM1i new soil moisture right after i precipitation Fi infiltration after i precipitation

Coming Soon Baseflow Calculations – modelled with Soil moisture conditions Daily Streamflow Simulation Applying the Model Acknowledgements: Barney Austin, Dr. Maidment, Richard Gu, Jerry Perales