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WUP-FIN training, 3-4 May, 2005, Bangkok
Hydrological modelling of the Nam Songkhram watershed
2
WUP-FIN Nam Songkhram Model Applications
VMod model for the entire watershed
HBV at least for the upper part of the Nam Songkhram upstream of Ban Tha Kok Daeng
3D lake and floodplain model for the lower part of the Nam Songkhram and tribuaries, including the largest floodplains
3
4
Elevation
13126 km2
Heights• min 135m• max 675 m
5
SAHATSAKHAN
KUMPHAWAPI
NONG_HAN PHANNA_NIKHOM
SAWANG_DAEN_DIN
PHEN
WARITCHAPHUM
SAKON_NAKHON
THA_UTHEN NAKHON_PHANOM
SISONGKHRAM
BAN_PHAENG PHON_PHISAI
BUNG_KAN
BAN_THA_KOK_DAENG SO_PHISAI
BAN_THA_KOK_DAENG/TEMP
Weather data
16 precipitation stations
Temperature data from one station
Evaporation, one station used
Some data gaps• Temperature missing
1994-2002• Some months missing
in Pan evaporation
6
1175
1432
2366
1339 1254
1128
1564
2290
2665
1796
1446
2943
1976
1984
1850 1979
Average yearly precipitation
7
Modelling: HBV
HBV model has been set up for the basin upstream of Ban Tha Kok Daeng
The size of the model area is 5029 km2
Ban Tha Kok Daeng
8
Modelling: HBV
Simple optimisation of the model parameters completed
Model results in calibration period (1987-1991) very good
• Measured to computed R2 0.93
Model result in test period (1992-1995) moderately good
• Measured to computed R2 0.76
9
Modelling :VMod
2D distributed hydrological model coupled with a 1D hydrodynamic river, reservoir and lake model
Physical model of the application area that takes into account variability in elevations, soil properties, vegetation, land use etc.
10
Landuse/Irrigated area
Landuse (1997) types are• Water• Agriculture• Irrigated agriculture• Evergreen/mixed forest• Deciduous forest/scrub
89% of landuse agriculture or irrigated agriculture
Irrigated 3280 km2 (24% of catchment, 2001)
New landuse data (2002)
11
Soils
Five soil types
80 % acrisol/plintic acrisol
Low water retention and conductivity
water
floodplain
alluvial soils
(plinthic) acrisol
slope complex
12
Modelling: VMod
1 km model grid (resolution can and probably will be increased)
Flow network computed from DEM and corrected
The number of landuse and soil classes has been reduced to make the calibration and use of the model easier and clearer
5 landuse classes
5 soil classes
13
Modelling: VMod
Irrigated agricultural land has been separated into it’s own land use class
River dimension and parameters have been modified
Still more work to be done with the river dimensions and flood plains
Calibration of the model has been started with the measurements from Ban Tha Kok Daeng
Ban_Tha_Kok_Daeng 68,108
14
Computed flow at Ban Tha Kok Daeng compared to measured data
The results (right) are much better than the previous results(left), but there is still room for more improvement
R2 is 0.92 in calibration period, 0.84 in test period
VMod flow computations
07/89 01/90 07/90 01/91 07/91 01/92 07/92
200
400
600
800
1000
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R2 is 0.92 in calibration period (1989-6/1992)
R2 is 0.84 in test period (1992-1995)
VMod flow computations
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VMod Model user interface
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VMod: Future tasks
Include the new data provided by the TNMC into the model
Develop further the agricultural water practices (water trapping, discharge and evaporation from paddy fields etc.)
Check the floodplains in the hydrological model
Add structures that may affect flow
Check river dimensions (cross sections)
Further calibration of the model
Include water quality and erosion components to the model and calibrate these
Clarify and execute scenarios (e.g. irrigation, land use and climatological changes)
18
Modelling: 3D
The EIA 3D lake and floodplain model has been set up for the lower Nam Sonkhram area• Begins at Ban Tha Kok
Daeng• Includes part of the
Mekong mainstream (endpoint Nakhon Phanom)
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Modelling: 3D
The main tribuaries of the Nam Songkhram have been included in the model (Nam Oon, Nam Yam, Huai Hi...)
Model calculation have been visually compared to data from inundated areas
Effect of Mekong mainstream waterlevel (backwater effect)
Sensitivity to parameter values has been analysed
Channel dimension and elevations have been modified (still in progress)
20
Flood duration
Flood arrival time
(First calculations)
21
Flood depth-
Mekong water level low
Flood depth-
Mekong water level high
22
3D: Future tasks
Include new river cross sections in to the model
Check grid heights
Include structures that affect flow (enbankments, dams, weirds)
Calibrate and verify the model
Include water quality calculations
Clarify and execute scenarios (e.g. irrigation, land use and climatological changes)
23
VIV Watershed Models
Two models:• HBV – simple rainfall-runoff model• VMod – distributed physically based/conceptual
hydrological model
Used e.g. for the watershed hydrological investigations and as a input for the 3D Lake model
24
HBV model
A simple rainfall-runoff model
Conceptual hydrological model
Catchment is handled as a homogeneous unit (lumped model)
Model parameters apply to the whole area
The model has three storages (surface, mid and ground) and river and lake storage
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HBV - Model Structure
Ssurf (surface storage)
Smid (mid storage)
Sground (groundw. st.)
Precipitation PET
Sriver (river st.)
etr
yield
Infiltration
Percolation
Ssurf (surface storage)
Smid (mid storage)
Sground (groundw. st.)
Precipitation PET
Sriver (river st.) qriver
qgw
qmid
etr
Infiltration
Percolation Slake (lake st.)
qlake
26
HBV – User Interface
27
HBV - Input
Input data (daily values)
Size of modelled catchment (km2)
Lake surface height (m) – lake surface area (km2) curve (optional)
Precipitation (mm/d), one station, or weighted sum of several stations
Potential evaporation computed from one of the following• Pan evaporation (mm/d) • Min and max temperature (°C), • Average temperature (°C), cloudiness (%) • Average temperature (°C), short wave radiation (MJ/d), wind
speed (m/s), relative humidity (%)
Average outflow (m3/s), one station
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HBV – Output and Results
01/01/1998 03/07/1998 01/01/1999 03/07/1999 02/01/2000
0
50
100
150
200
Computed result as daily values
Average outflow (m3/s)
Optionally• Model state variables (mm)
• Evaporation (mm/d)
• Corrected precipitation (mm)
• Lake surface height (m)
• Lake area (km2)
02/06/199403/07/199402/08/199402/09/199402/10/199401/11/199402/12/199401/01/199501/02/199503/03/199503/04/199503/05/1995
200
400
600
800
1000
1200
1400
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VMod
Distributed physically based/conceptual hydrological model
Takes into account variability in elevations, soil properties, vegetation, land use etc.
Based on grid representation
Possible uses:• Effect of land-use changes to catchment hydrology• Simulation of the effect of land-use changes to water
quality • Simulation of the effect of climate changes to catchment
hydrology
30
Model grid - 3d view
View from Vortsjarvi river watershed (in Estonia)
31
VMod - Model User Interface
Database
GUI - GIS data handling - timeseries data handling - model run management - data visualisation - statistical data analysis
GIS data - raster - vector
Timeseries - meteorological - hydrological
Model
32
VMod – User Interface
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VMod – Model Structure
precipitation dataevaporation data data interpolation
grid box module
ground water module
river/lake module
elevation data
landuse data
2d model grid
interpolated precipitation interpolated temperature
evaporationinfiltration/overflow
Storage sizeFlow in soil layers
river flowslake surface height
computed valuesmodulesmodel data
precipitation dataevaporation data data interpolation
surface layer
soil layers
river/lake module
elevation data
Landuse and soil data
2d model grid
interpolated precipitation interpolated temperature
evaporationinfiltration/overflow
river flowslake surface height
computed valuesmodulesmodel data
Flow to rivers/soil layers
34
VMod model structure
One grid box computation Model grid & flow network
Flow from grid boxesabove
overflow
interflow
kerros 2
kerros 1
Pintakerros
Evapotranspiration
ground water flow
Flow to river
Soil layer 2
Soil Layer 1
Surface layer
Wilting pointField capacity
Maximum capacity
Precipitation
35
VMod processes
Interpolation and correction of weather data• Precipitation and temperature• Height correction based on elevation
Interception of precipitation in vegetation Infiltration of water in the soil
• Calculated based on the Green-Ampt model
Water accumulation in pond storage and surface runoff• If the soil is unable to infiltrate all water
36
VMod processes
Evaporation from interception storage, ground surface and through vegetation from soil
• Calculated from potential evapotranspiration (PET)• Affected by pond and interception storages, soil moisture, and
vegetation data
Plant growth• Seasonal crop growth based on temperature sum • Perennial plants leaf area index change based on temperature
sum
Water movements• Between soil layers• From grid cell to another• From grid cell to river or lake
In winter conditions more processes available
37
Surface runoff
Surface runoff is generated when• Soil cannot infiltrate all water• Pond storage is full
Surface runoff is assumed to occur as sheet flow in the width of the entire grid cell
In surface runoff water flows• To the next lowest grid cell• To a river in the grid cell
The amount of surface runoff depends on• Ground surface flow resistance• Ground slope
38
Soil model
Soil is divided in two layers
Layers divided in two parts at field capacity• Water content above field capacity water can flow out of
soil layer• Water content below field capacity water can’t flow out of
soil layer, but is available to plants From soil layer water flows
• To the next lowest grid cell• To a river in the grid cell
Amount of flow is influenced by• Horizontal conductivity of the soil• Ground water height• Grid cell slope
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River model
Routing of water in rivers
Uses kinematic approximation of the St. Venant equations
Flow speed in rivers depends on• Channel cross section• Bottom slope• Water depth• Water level in the downstream
grid cell (optional)
Solved numerically
40
Lake model and other models
Lake model• Lakes are handled as storages
• Water level changes are linearly related to volume changes• Volume changes are computed from inflow, outflow, precipitation
and lake evaporation
• Outflow from the lake depends on the water height in the lake
• Rating curve can also be used
Erosion model
Water quality model
41
VMod – Input
Precipitation (mm/d), at least one station
Potential evaporation computed from one of the following• Pan evaporation (mm/d) • Min and max temperature (°C), • Average temperature (°C), cloudiness (%) • Average temperature (°C), short wave radiation (MJ/d),
wind speed (m/s), relative humidity (%)
Average outflow (m3/s), at least one station
Water quality measurements
42
VMod – Input
Digital elevation model of the catchment (e.g. 50m resolution)
Land use data for the catchment
Soil type data for the catchment (in new version of VMod)
Catchment boundary line
Shorelines of lakes in the catchment
Optionally digitized river network of the catchment
43
VMod – Output and Results
Average river flow (m3/s) at any point within the catchment
Other model variables at any point within the catchment
• Evaporation (mm/d)• Corrected precipitation (mm)• Lake surface height (m)• Ground water height (m)• …
Siem Reap
05/99 06/99 07/99 08/99 09/99 10/99 11/99 12/99 01/00
0
10
20
30
40
50
60
m3
/s
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Watershed Model’s Benefits
Integration of the spatial and temporal environmental information
Water resource investigations
Gaining better understanding of hydrological processes
Support for lake modeling
Forecasting possibilities
Water quality estimation
MRCS/WUP-FINwww.eia.fi/wup-fin