Abstract:
To make accurate and reliable quantile estimates at ungauged catchments, two
approaches were followed and studied in Abbay river basin: hydrologic regionalization
and application of the event based Geomorphoclimatic Instantaneous Unit Hydrograph
( GcIUH) concept.
Abbay river basin was divided into 129 watersheds and 45 Geomorphologic and climate
parameters were extracted for each watershed using Arc Hydro/GIS, WinDisp and
New_LocClim softwares. Out of these the 21 most important parameters were selected
through Principal Component Analysis. Cluster analysis option of SPSS was used to
cluster (group) these 129 watersheds into a convenient riumber of groups depending on
the similarity of the 21 input parameters and with a reasonable classification threshold.
This grouped Abbay river basin into hydrologically homogeneous regions. This
hydrologic regionalization was perceived from a hydroclimatological and
physiogeographical point of view; and verified with representative recorded flow data
from within the basin.
After all, the research resulted in the delineation of five stable regions. Regions one and
two cover much of the area of the eastern half of the basin, while region three is the area
covering most of the boundary of the lakes Tana and Finchaa. Region four mainly covers
the area following the western border of the study area where as region five covers the
southern portion of the western half of the basin. Out of these five, regions one, two, four
and five have adequate number of recorded flow data. These four regions were tested for
homogeneity and heterogeneity using discordance tests and H statistics respectively, and
found homogeneous. On the other hand, the prediction power of the Geomorphoclimatic Instantaneous Unit
hydrograph concept was assessed in one of the catchments in Abbay river basin,
Andassa. The findings are very encouraging, suggesting that the GclUH concept can be
indeed become a useful tool in many regions where very little or no data are available to
the hydrologist
Further study on the companson of data and information transfer from a region of
completely different regional taxonomy and synthetic flow generation methods would
make the study more complete and useful for decision support system.
Key words: Abbay river basin; Regionalization; GcIUH; Ungauged catchments; Cluster analysis
