Application of Remote Sensing and GIS for Groundwater Potential Zone Mapping in Northern Ada'a Plain (Modjo Catchment)
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Date
2007-03
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Addis Ababa Universty
Abstract
An integrated approach with remote sensing, Geographic Information Systems (GIS) and more
traditional fieldwork techniques was adopted to map the groundwater potential sites in the central
rift valley area of Northern Ada`a Plain (Modjo Catchment). Catchment delineation was done in
ILWIS 3.3 DEMHYDROPROCESSING module. Digital image processing of enhanced color from
Landsat ETM+ was interpreted to produce thematic maps such as lithology, lineaments, land
use/cover and geomorphology. Contours and drainage lines were digitized for slope and drainage
density mapping. GIS analysis of distance for lineaments, density for drainage, slope for elevation
and reclassification were done for each factor maps. Selected springs and wells were visited to
study their topographic and hydrogeological setting. Digital Elevation Models (DEM) derived
from contours and acquired in the Shuttle Radar Topographic Mission (SRTM V-3) were
compared in relation to drainage and lineaments extraction, landform mapping and catchments
delineation. DEM derived from SRTM V-3 using DEMHYDROPROCESSING are better for
catchments delineation and landform mapping than those derived from contours. A model that
incorporates Weighted Linear Combination (WLC) was built using ARCGIS 9 model builder
engine. The model was executed and groundwater potential map was generated. The spatial
distributions of the various ground water potential zones obtained from the model generally show
regional patterns of lithology, landform and lineaments. Spatially the very good and good
categories are distributed along plain geomorphic units, near to lineaments, less dense drainage
density and where the lithology is affected by secondary structure and having interconnected pore
spaces. Groundwater potential zones demarcated through the model are in agreement with
borehole data collected from the area. The validity of the model developed was tested against the
borehole data, where out of 107 boreholes 50 are on very good and good zones, 37 on moderate
zones, 14 on fair and 6 on poor zones. Moreover out of 52 bore holes with discharge rate from 24
l/s to 69 l/s are on the very good and good zones, which reflects the actual ground water potential.
Although some wells exist in all ground water potential zones, the best yielding wells lie in the very
good and good ground water prospect zone. The results demonstrate that the integration of remote
sensing, GIS, traditional fieldwork, and geomorphology provide a powerful tool in the assessment and
management of water resources and development of groundwater exploration plans.
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Keywords
Modjo Catchment