| Abstract | The scarcity of water, acutely experienced when the dry season begins with limited water,
no efficient criteria for water allocation and limited scope for further expansion of water
supplies, can be pertinently addressed by a flexible system of allocation based on suitable
decision-making criteria. The overall objective of the study is to develop a model for
allocating water to the conflicting users taking the technical, equitable, economic and
environmental aspects into consideration. The specific objectives are to develop a hydroeconomic
equity support water allocation model to maximize the level of satisfaction
and/or maximize the net economic benefit from different sectors in the basin; to estimate
the net economic return from different water use sectors; to study the current allocation
system and to evaluate the demand and supply situation in the Chao Phraya River basin of
Thailand and; to apply the developed model to the Chao Phraya basin to improve
allocation efficiency and user satisfaction level.
The study develops an integrated water allocation model (IWAM), which mainly
comprises a reservoir operation model (ROM), a module for estimation of net economic
return (NER) to different water use sectors and a water allocation model (WAM). ROM
determines the available water, which is used as an input to WAM. The water allocation
model considers two single objective functions. The first single objective function (OF1)
allocates water to maximize the level of satisfaction. This objective function is formulated
in two ways; maximization of average level of satisfaction of all the sectors (OF1a) and
maximization of minimum level of satisfaction among the sectors (OF1b). A minimum
operator is used in OF1b to distribute the stress level equally among the different water use
sectors. The second single objective function (OF2) allocates water to maximize the net
economic benefits from different water use sectors. The model also considers a multiobjective
function (OF12), which is a combination of two single objectives. A classical
approach to linear programming is applied to optimize the allocation with OF1, OF2 or
OF12. The SICCON (simultaneous compromise constraint) Technique and the Weighting
Technique is used to optimize water allocation when OF12 is used. The optimization tool
Solver in Microsoft Excel is used and the optimization program is written in visual basic
with a user-friendly interface. Different techniques have been used to estimate the NER of
50, 21738, 205, 3 and 10 US$/1000m3 to water use in agriculture, domestic, industry,
hydropower, and salinity control sectors.
iv
The study reviews the existing allocation system and analyses the current allocation
practices in the Chao Phraya River basin in Thailand where acute shortages are often
experienced during the dry season. The developed model is applied to the Chao Phraya
River basin and the allocation results are compared with the existing system of allocation
in terms of level of satisfaction and the economic benefits from different water use sectors
for the dry season of 2004. The operation of Bhumibol and Sirikit reservoirs in the basin is
simulated using the ROM and the applicability of IWAM is demonstrated with several
scenarios by giving priority, specific % of normal demand (minimum demand to be
satisfied) and giving different weights in case of multiobjective function. When OF1 is
considered, the model first allocates water to a sector with the lowest normal demand and
then to the sector with next higher normal demand whereas in OF2 the model first allocates
water to sector with highest net economic return, followed by the next higher one. When
priorities or specific % of demand are considered the model allocates water first to those
sectors with priority or specified minimum demand over other sectors. OF12 with
maximization of minimum level of satisfaction and net economic benefit using SICCON
Technique is considered as a compromised allocation between the two objectives, with
possible equal distribution of stress and higher economic benefit of about 720 million
USD when compared to that of the actual release in the Chao Phraya River basin.
The significance of the model results lies in the flexibility in allocating water to different
sectors with maximization of level of satisfaction and net economic benefit with the
limited available water. The model can be made economically efficient by estimating the
marginal net benefits from different water use sectors to infer NER, instead of average net
benefit used in the present study. Further, the concept of benefit sharing of the proposed
water allocation model can be improved and adapted to a transboundary river basin. |