4. Generating water resource distribution
map
4-1:Definition of water resource distribution map
The water resource distribution map shows
the amount of available water at each grid cell,
assuming that water can be pumped from the
neighboring river. The available water on a grid
cell is estimated, using the elevation difference
and the distance between the closest river and
an object-grid-cell. As shown in figure 4-1, the
distance is defined along the route through
which the water flowed down.
Figure 4-1 Elevation difference
and distance of runoff route
4-2:Estimation of the available water
The authors apply “potential energy” concept
in order to take the elevation difference into account. And it is assumed the available
water is in inverse proportion to the distance in order to take the distance into
account.
4-3:Generating water resource distribution map
Drainage network whose discharge is more than “D” is extracted from the
discharge map in chapter 3. Constant
“D” is determined for each river from
the annual least discharge. If the
runoff on a grid cell runs down along
DDM and reaches the drainage
network like figure 4-1, the elevation
difference and the distance are
calculated for each grid cell. When
the workload is given as constant “W”,
the formula for finding the available
water is:
AW[ m
3/y]: available water, W[ KWy]:
workload, g[ m/s
2 ]: acceleration of
gravity, E[ m]: elevation difference,
d[ m]: distance from the drainage
network.
We can calculate the available
water on all grid cells by the
above-mentioned formula. For
example, water resource distribution
map of Mekong basin is shown at
figure 4-2.
Figure 4-2 Water Resource Distribution Map on Mekong Basin
5. Conclusions and Future works
5-1:Conclusions
We generated Discharge Map using water balance model and DDM. But water
balance model has several problems. At first, the estimation of evapotranspiration is
overestimated in winter because water balance model takes the snowfall as the
rainfall. Secondly, the estimation of runoff is not very accurate because the model
doesn’t separate groundwater runoff from surface runoff.
We generated Water Resource Distribution Map using Discharge map. But this
output has problems. The author does not take reservoirs and dams into account in
calculating the available water. If reservoirs and dams are taken into account, water
resource distribution map will become a more accurate. The improved result may
help in planning of irrigation system in order to enhance the agricultural productivity
as well as food demand of increasing world population.
5-2:Future work
Demand for water can be estimated using population and agricultural productivity
at each grid cell. Comparing the demand for water with the available water, we are
able to evaluate whether each river can meet the demand or not.
6. References
-
An and Tateishi (1995): Estimates of Global Land Evapotranspiration and Water
Resources Using GIS Techniques
- Ochi S. (1999): Algorithm for Generating Drainage Direction Matrix using
DEM(GTOPO30) and DCW, Photogrammetry and Remote Sensing ,Vol.38, No.3
- Nogami M. (1998); An Algorithm and a C-Program Source for Automated Drainage
Network Extraction, Theory and Application of GIS, Vol. 6, No.1
