applying txrr to texas coastal basins routing to the streams
Skip this Video
Download Presentation
Applying TxRR to Texas Coastal Basins – Routing to the Streams

Loading in 2 Seconds...

play fullscreen
1 / 12

Applying TxRR to Texas Coastal Basins Routing to the Streams - PowerPoint PPT Presentation

  • Uploaded on

Applying TxRR to Texas Coastal Basins – Routing to the Streams. Victoria Samuels CE 394K.2. TxRR Water Balance. It Rains! P i at t i Initial Abstractions subtracted Runoff produced Excess goes to Infiltration Base Flow calculated from SM parameters

I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
Download Presentation

PowerPoint Slideshow about 'Applying TxRR to Texas Coastal Basins Routing to the Streams' - maree

An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.

- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
txrr water balance
TxRR Water Balance
  • It Rains! Pi at ti
  • Initial Abstractions subtracted
  • Runoff produced
  • Excess goes to Infiltration
  • Base Flow calculated from SM parameters
  • Base Flow + Direct Runoff = Stream Flow

Precipitation P

Initial Abstraction


Direct Runoff QD

Infiltration F

Maximum Soil Moisture SMMAX =

Soil Moisture SM + Soil Retention S

Stream Flow

Base Flow QB


(not modelled)

time variables
Time Variables










In “i-1” time (t1):

QB2, SM2 QB1, SM1

Time between Precipitation Events = ti = t2 – t1

In “i” time (t2):

QB2, SM2 QB1, SM1

direct runoff
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


base flow recession
Base Flow - Recession

QB2 = QB1 * Kt2 – t1

QB2 base flow rate at time t2

QB1 base flow rate at time t1

K recession constant (0.966 subsurface flow,

0.992 groundwater runoff)

t2-t1 elapsed time

  • Part of the streamflow that flows out long after a precipitation event
  • Can be groundwater runoff, subsurface runoff, or a combination of the two
base flow reaction to precipitation
Base Flow – Reaction to Precipitation
  • Base flow increment either proportional to amount of precipitation or infiltration
  • Related to soil moisture, ie base flow is larger when soil moisture is larger

QBnew = wB * Fi * (SM2i/SMMAX)

QBnew = wB * Pi * (SM2i/SMMAX)

QBnew base flow increment

wB base flow coefficient or weighting factor

SM2isoil moisture right before i precipitation

SMMAX maximum soil moisture

base flow which equation
Infiltration Equation is more conceptually correct

However, when Fi 0, QBnew  0, despite if there is a large amount of precipitation (initial abstraction is large enough to take all of the precipitation, soil retention large enough)

If a large initial abstraction is realistic, use Fi equation. If not realistic, use Pi equation

Base Flow – Which Equation?

QBnew = wB * Fi * (SM2i/SMMAX)

QBnew = wB * Pi * (SM2i/SMMAX)

base flow computations
Base Flow - Computations

New Base Flow: QB1i = QB2i + QBnew

Amount of New Base Flow (volume): QBV = (QB2 - QB1) / ln K

Used for daily continuous simulations

Total volume of Base Flow from initial base flow as

t2  inf, QB2  0:

QBV = -QB1 / ln K

Used for event by event simulation

stream flow simulation then
SCS Unit Hydrograph

Assumption that 37.5% of direct runoff reaches outlet before peak flow is reached

In hours

Tl= lag time = b * A0.6

b coefficient from 0.4 – 1.5

A drainage area (sq mi)

Tp = time to peak = 12 + Tl

Tb = base time = 5 * Tp

Qpeak = 484 * A * QD / Tp

Stream Flow Simulation - Then









stream flow simulation now
Stream Flow Simulation - Now
  • Cascade of identical completely mixed linear reservoirs
  • ki = detention time of each reservoir, Ni = number of reservoirs, t = time increment, ui(t) = discharge
  • Gamma distribution allows Ni to be a non-integer value, (Ni-1)! is replaced by the gamma function G(Ni)
  • Input to each reservoir is output from reservoir upstream

Acknowledgements: Dr. Francisco Olivera

stream flow simulation reservoirs
Stream Flow Simulation - Reservoirs

C2,out = Co(t/q)e-t/q

Cout = Coe-t/q



N =N

N = 2

N =1

CN,out = Co * 1/(N-1)! * (t/q)N-1 * e-t/q

Substitute: q = ki, N = Ni, using the relationship Q/V = 1/ki,

and a little handwaving:

ui(t) = 1/ki * e-t/ki * 1/(Ni-1)! * (t/ki)Ni - 1

Acknowledgements: Dr. Desmond Lawler