1. WUP-FIN training, 3-4 May, 2005, Bangkok Hydrological modelling of the Nam Songkhram watershed

2. 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. 3

4. 4 Elevation 13126 km 2 Heights min 135m max 675 m

5. 5 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. 6  1175  1432  2366  1339  1254  1128  1564  2290  2665  1796  1446  2943  1976  1984  1850  1979 Average yearly precipitation

7. 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 km 2 Ban Tha Kok Daeng

8. 8 Modelling: HBV Simple optimisation of the model parameters completed Model results in calibration period (1987-1991) very good Measured to computed R 2 0.93 Model result in test period (1992-1995) moderately good Measured to computed R 2 0.76

9. 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. 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 km 2 (24% of catchment, 2001) New landuse data (2002)

11. 11 Soils Five soil types 80 % acrisol/plintic acrisol Low water retention and conductivity water floodplain alluvial soils (plinthic) acrisol slope complex

12. 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. 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

14. 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

15. 15 R2 is 0.92 in calibration period (1989-6/1992) R2 is 0.84 in test period (1992-1995) VMod flow computations

16. 16 VMod Model user interface

17. 17 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. 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)

19. 19 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. 20 Flood duration Flood arrival time (First calculations)

21. 21 Flood depth- Mekong water level low Flood depth- Mekong water level high

22. 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. 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. 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

25. 25 HBV - Model Structure

26. 26 HBV – User Interface

27. 27 HBV - Input Input data (daily values) Size of modelled catchment (km 2 ) Lake surface height (m) – lake surface area (km 2 ) 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 (m 3 /s), one station

28. 28 HBV – Output and Results Computed result as daily values Average outflow (m 3 /s) Optionally Model state variables (mm) Evaporation (mm/d) Corrected precipitation (mm) Lake surface height (m) Lake area (km 2 )

29. 29 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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31. 31 VMod - Model User Interface

32. 32 VMod – User Interface

33. 33 VMod – Model Structure precipitation data evaporation data data interpolation grid box module ground water module river/lake module elevation data landuse data 2d model grid interpolated precipitation interpolated temperature evaporation infiltration/overflow Storage size Flow in soil layers river flows lake surface height computed valuesmodulesmodel data precipitation data evaporation data data interpolation surface layer soil layers river/lake module elevation data Landuse and soil data 2d model grid interpolated precipitation interpolated temperature evaporation infiltration/overflow river flows lake surface height computed valuesmodulesmodel data Flow to rivers/soil layers

34. 34 VMod model structure One grid box computation Model grid & flow network Flow from grid boxes above overflow interflow kerros 2 kerros 1 Pintakerros Evapotranspiration ground water flow Flow to river Soil layer 2 Soil Layer 1 Surface layer Wilting point Field capacity Maximum capacity Precipitation

35. 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. 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. 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. 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

39. 39 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. 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. 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 (m 3 /s), at least one station Water quality measurements

42. 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. 43 VMod – Output and Results Average river flow (m 3 /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) …

44. 44 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

45. MRCS/WUP-FIN www.eia.fi/wup-fin