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Raingauge at Kejema

Hydrological studies in Umbulo Wacho


Geological Background

The Umbulo Wacho project area is located 15 km west of Awassa and is approximately 3000 ha. The study area forms part of the Awassa caldera which is within the African rift valley which is tectonically active and widening. The project area forms a basin infilled with volcanic ash deposits. The project area is defined as the catchment area draining into a temporary pond (lake in the previous report) called Derba pond by the Ethiopian Geological Survey. The project area contains several gullies and Derba pond drains out through a known geological fault.

Gullies in Umbulo Wacho


Gully flowing through Derba Pond

One of the drainage holes in the fault through Derba Pond Full and empty 24hrs later



Analysis of the meteorological data available from the National Meteorological Station at Awassa shows that the mean annual rainfall is estimated to be 985 mm. The distribution from average rainfall records is unimodal, on average some rainfall occurring in all months, mainly from April to October. Average mean temperatures are 15-20°c, relative humidity between Oct-Jun is 67 % and between Jul-Sep, 78 %. Evaporation between Oct- Jan is 300 mm, Feb - May 300 mm, Jun- Sep 550 mm. The pond surface area is approximately 1 km2.

5 collecting raingauges were installed as well as one recording raingauge at the Bureau of Agricultures extention office in Korangoge, just outside of the project area.

Map of the Umbulo Wacho project area


Farmer recorded rainfall for 2005

All farmers had read their raingauges, however the extention agents and the University researchers had not collated all the data, hence why there is no full record for farmer 1. Annual rainfall ranged from 600mm- 1000mm across the project area

Rainfall at farmer raingauges in Umbulo Wacho

Copyright © Martin Hollingham