Agriculture Reference
In-Depth Information
8.2 M
ETHODOLOGY AND
D
ATA
C
OLLECTION
The study involved data collection and modelling followed by analysis of
modelling results. The data collected range from water users and their
demand, dam and reservoir characteristics, groundwater storage data, water
supply sources and return flow receivers, streamflow data and climate data
such as rainfall and evaporation. Field surveys and field measurements were
conducted to estimate irrigation water consumption and extent of irrigation
development for various irrigation technologies. The extent of irrigation
development of various technologies were verified with data from the
Ministry of Agriculture (MOFA) and Agricultural Extension Officers and
were confirmed with satellite images taken over the study area within the
same period. Dam and reservoir characteristics were obtained from
institutional reports. Information on groundwater availability was taken
mainly from the water balance study conducted in the Atankwidi catchment
by Martin (2006).
There was lack of adequate data for a full rainfall-runoff analysis. Two years
of streamflow data were available for two of the catchments (Yarigatanga
and Atankwidi) and 44 years of rainfall data from the closest station to the
catchments. As a result only two years of rainfall and streamflow data could
be used for the rainfall-runoff analysis.
The Water Evaluation and Planning software (WEAP) modelling software
was used for analysing the impact of upscaling irrigation development.
WEAP is a tool for examining alternative water development and
management strategies (WEAP, 2009). It operates on water balance
accounting principles. WEAP is distinguished by its integrated approach to
simulating water systems and by its policy orientation. It is not reliable for
detailed hydrological and water quality analysis, but it has the flexibility of
working with other hydrology and water quality software such as Modflow
and QUAL2K.
The analysis using the WEAP model involved five steps, beginning with the
parameterization of the model, followed by the calibration and validation
stages, then the development of scenarios, and finally the analysis of the
results.
Analysis of the impact on Lake Volta and on hydro-power generation was
based on a historical data set of lake levels, turbine releases and electricity
generation, and the development of a straightforward spreadsheet-based
Waflex model (Savenije, 1995).
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