# libHydro by fALBJEh

VIEWS: 5 PAGES: 20

• pg 1
```									libHydro
LibHydro

 LibHydro in Excel
 LibHydro in ArcMap
LibHydro in Excel
Functions list that is called by Excel VBA
LossGreenAmpt
The Green and Ampt model computes the precipitation loss on the pervious
area in a time interval as:
 Ft    S f 
ft  K                
0              Moisture Content
      Ft       
Li                              i
ft: Infiltration Rate (L / T)
L(t)                      K: Hydraulic Conductivity (L/T)
Ft: Cumulative loss at time t (L)
Sf: Wetting Front Suction Head (L)
ft                 ΔΘ :Moisture Deficit (-)
Φ                               Φ: Porosity (-)
θr
Θi: Initial Moisture Content (-)
θe
Li: START INITIAL LOSS
θi          Δθ                L(0): START INFILTRATION
L(END): FINAL INFILTRATION
LossInitialConstant

Basic Concept for LossInitialConstant
Et = Et (Impervious) + Et (pervious)
Et (Impervious) = Pt
0           if ΣPt < Ia
Et (pervious) =     Pt – fc     if ΣPt > Ia and Pt > fc
0           if ΣPt > Ia and Pt < fc

Et : Excess at time t
Pt : Precipitation at time t
Ia: Initial Loss
fc: Constant Loss Rate
LossSCSCurveNumber

Pe = Accumulated precipitation excess at time t (mm)
P = Accumulated rainfall depth at time t (mm)
Ia = Initial abstraction (initial loss) (mm)
S = Potential maximum retention (mm)

(For SI Unit)
CN = Curve number (30 < CN < 100)
Unit hydrograph
Precipitation (mm)

Loss Rates (Green Ampt, Initial
Constant or SCS Curve Number

Excess (mm)
Unitgraph Size
# of unitgraph ordinates
Unitgraph (Snyder, SCS or Clark)
Unit Runoff (m3/s per mm of excess)
Unitgraph Convolution

Runoff (m3/s)
Unitgraph Clark
Parameters
Time of Concentration:
The time of flow from the farthest point on the watershed to the outlet
Storage Time:
Storage constant R with the linear reservoir model
St = R*Ot

Process of the Unitgraph Clark
1. Estimate the contribution area with A         t
1.5
t
2. time-area relationship
t
 1.414  fort  c
t 
A          c       2
Ot  C A I t  C B Ot 1
1.5
At               t               tc
 1  1.4141  
 t        fort 
A                c               2             t
CA 
3. Calculate the average inflow It to the storage at time t                           R  0 .5  t
4. Calculate the unitgraph ordinates with the following equations                CB  1  C A
Ot 1  Ot
Ot 
2
Snyder’s Unit Hydrograph
Input Variables                                           Output Variable:
tp : Snyder Lag (hr)                                     unitgraph ordinates (m3/s per mm of excess)
Cp: Snyder Cp
A: Basin Area (km2)
tR: Time interval                                                                         tpR=tp-(tr-tR)/4
Standard UH                                                                                   (when tpR≠5.5tR)
(when tpR=5.5tR)

Discharge per unit area
tr
tR
Discharge per unit area

tp                                                                  tpR
qP=2.75*Cp/tp
qp                                                                 qpR                       qPR=qP*tp/tpR
W75

W50

tb
Time                                                                      Time
SCS Dimensionless Hydrograph

CA        qp: Peak runoff (m3/s)
Tr                            qp             C:2.08 for SI
Tp        A: Basin Area (km2)
Excess Rainfall                          Tp: Time of rise
Tr
Tr/2                                Tp        tp   Tr: Excess Duration (hour)
2        Tp: lag time (hour)
tp
t p  0.6Tc     Tc: Time of concentration (hour)

Direct Runoff

qp
Tp
tb
BaseflowHEC1
(A) total flow > recession threshold at falling limb
or total flow is at rising limb
Qb  Q0  K t
Qb: base flow
Q0: initial base flow
K: recession constant
T: time                      Discharge
( t t r )                                         recession
Qt  Qr  K                                        Total flow    threshold
Qt: total flow
Qr: flow where recession starts
tr: time when recession starts
Time
(B) total flow < recession threshold at falling limb

Qb  Qt  DirectRuno ff                         Baseflow
Muskingum Routing
Prism Storage
Wedge Storage

St  ( PrismStorage)  (WedgeStorage)
 KOt  KX ( I t  Ot )                 Oi  (ca  cb ) I i 1  cb I i  (1  ca )Oi 1
St  St 1 I t  I t 1 Ot  Ot 1      where
            
t           2           2                      2t
ca 
2 K (1  x)  t
St: Storage at time t
It: Inflow at time t                   t  2 KX
cb 
Ot: Outflow at time t                2 K (1  x)  t
K: Muskingum K
X: Muskingum X
Muskingum Routing

Feasible region for         2
Muskingum model parameter

t 1
1      K   1      K
   
2(1  x) t 2 x
0        0.5          1.0
X
Feasible region
EarthDistance in ArcMap
LibHydro in ArcMap
Model Builder Input Box
for LossInitialConstant
Loss Initial Constant
Excess with Loss Initial Constant Method

0.16
0.14
0.12
Height(mm)

0.1
Precipitation
0.08
Excess
0.06
0.04
0.02
0
1:00 AM
2:00 AM
3:00 AM
4:00 AM
5:00 AM
6:00 AM
7:00 AM
8:00 AM
9:00 AM
11:00 PM
12:00 AM

10:00 AM
time
Model Builder Input Box
for Snyder Unitgraph
Snyder Unitgraph

Rainfall and Runoff Time Series
0.16                                                                1.6
0.14                                                                1.4
Precipitation
Precipitation (mm)

0.12                                                                1.2

Runoff(cms)
Runoff
0.1                                                                1
0.08                                                                0.8
0.06                                                                0.6
0.04                                                                0.4
0.02                                                                0.2
0                                                                  0
9:36 PM   12:00 AM   2:24 AM   4:48 AM   7:12 AM   9:36 AM    12:00 PM
Time
Model Builder Process

```
To top