Agriculture Reference
In-Depth Information
or all of the resources are used, whichever happens first. The Supply
Preference parameter allows users to define which source should be used in
priority to supply water to a demand site. WEAP will attempt to supply all
of the demand with sources having highest preference level, only using lower-
level sources if the high-level sources do not have sufficient supply (WEAP,
2009).
When the WEAP model is run it simulates monthly time steps of each year,
each scenario and all aspects of the water system, including demand site
requirements
and
coverage,
streamflow,
in-streamflow
requirement
satisfaction, and reservoir storage.
Model results can be generated in WEAP in the form of tables and charts.
The results in table formats can be imported into Microsoft excel for
processing.
8.3.2 Model setup
The WEAP model was setup to best fit the water resources and water-use of
the study area. The study models the expected level of irrigation
development and other water uses over a period of 20 years with changing
climatic conditions. The water year for the study area is May to April. Data
for the 2005/2006 water year is used for the current account. The model
represents: (1) the three catchment areas together with their characteristics;
(2) the surface water and groundwater characteristics (quantity); (3) the
water uses and their corresponding sources as well as return flows; (4) the
water reservoirs in the catchments; (5) water losses (evaporation and return
flows); (6) hydrological interactions between streamflow and groundwater;
and (7) the rainfall variability in the study area.
In the WEAP model setup, in each of the three catchments, the main river
has three tributaries. This is a simplification of the actual situation, where
the river has several small tributaries on which the small reservoirs have
been developed. As a result the small reservoirs are also lumped onto the
tributaries. In the WEAP model a combined set of tributaries also have their
small reservoirs lumped onto the resulting tributary. In lumping the small
reservoirs, their volumes V (in m
3
) and surface areas A (in m
2
) are summed
up separately then compared with the small reservoir characteristics
developed by Liebe et al. (2005) and confirmed by Annor et al. (2009)
(Equation 8.1). The volume elevation curve is then generated from Equation
8.2 which Liebe et al. (2005) used, with d being the maximum depth (m).
The volume elevation curve of the lumped small reservoirs is also guided by
the stochastic analysis performed on an ensemble of reservoirs in the Upper
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