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

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4

Elevation

13126 km2

Heights• min 135m• max 675 m

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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

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1175

1432

2366

1339 1254

1128

1564

2290

2665

1796

1446

2943

1976

1984

1850 1979

Average yearly precipitation

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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

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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

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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.

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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)

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Soils

Five soil types

80 % acrisol/plintic acrisol

Low water retention and conductivity

water

floodplain

alluvial soils

(plinthic) acrisol

slope complex

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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

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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

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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)

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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)

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Flood duration

Flood arrival time

(First calculations)

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Flood depth-

Mekong water level low

Flood depth-

Mekong water level high

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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)

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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

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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

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HBV – User Interface

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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

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Model grid - 3d view

View from Vortsjarvi river watershed (in Estonia)

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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