The Ethiopian Rift Valley lakes: chemical characteristics of a salinity-alkalinity series

Hydrobiologia ◽  
1994 ◽  
Vol 288 (1) ◽  
pp. 1-12 ◽  
Author(s):  
Elizabeth Kebede ◽  
Zinabu G. Mariam ◽  
Ingemar Ahlgren
Keyword(s):  
Rift Valley ◽  
Ethiopian Rift ◽  
Chemical Characteristics ◽  
Rift Valley Lakes

Spatial and Temporal Variability in Suspended Sediment Yield for two tropical mountain catchments draining into the Southern Ethiopian Rift Valley.

2021 ◽  
Author(s):  
Tilahun Alemayehu Kasaye ◽  
Guchie Gulie ◽  
Margaret Chen ◽  
Gert Verstraeten
Keyword(s):  
Suspended Sediment ◽  
Sediment Yield ◽  
Rainy Season ◽  
Rift Valley ◽  
Sediment Load ◽  
Ethiopian Rift ◽  
Alluvial Fans ◽  
Tropical Mountain ◽  
Rift Valley Lakes ◽  
Gauging Station

<p>Complex terrain tropical mountainous catchments are typically characterized by intense rainfall events, flash floods and high erosion rates with large variability over short distances. Whilst these processes are known, little quantitative information on the spatiotemporal variability in suspended sediment yield (SY) of African tropical mountain environments is available. Here, we provide such data for two catchments in the Southern Ethiopian Rift Valley characterised by annual rainfall of 700 to 1000 mm concentrated in the rainy season from April to October. In total 6 gauging stations were installed along Elgo (298 km²) and Shafe (191 km²) rivers which have their headwaters in the Gamo Highlands (max. elevation 3500 m) and run into the rift valley lakes of Chamo (1107 m) and Abaya (1169 m), respectively. For each river, a gauging station was installed where they enter the lakes as well as at the apex of extensive alluvial fans that developed in the graben lowlands, enabling to quantify the buffering capacity of the fans. For Elgo, two extra stations in the highlands were installed to monitor downstream changes in SY. At all stations, discharge (Q) was measured at 10-min resolution using a pressure diver during in 2018-2019. Additionally, 1542 samples were taken to measure the suspended sediment concentration (SSC), and these were used to establish sediment rating curves in order to calculate total suspended SY from the continuous discharge records. Observed SSC varies between 0.04 and 111.48 g/l for discharges ranging between 0.005 and 227.20 m³/s, whereas annual SY varies between 1133 and 6373 t/km²/year. Both SSC and SY values are in line with those reported for other highland rivers in Ethiopia and in line with SY values for other tropical mountain catchments in the world. A strong temporal variability in SSC and SY is observed and can be explained mainly due to changes in hillslope sediment supply throughout the seasons. Peak sediment transport is mostly concentrated in the first two months (May to June) of the rainy seasons accounting for about 60% of the total SY of the season. At the start of the rainy season, topsoil is loose because of tillage operations that prepare the soil for cultivation. Furthermore, vegetation cover is at its lowest value. Throughout the rainy season, vegetation cover increases and hence soil erosion and sediment yield declines.  Comparing the SY of the various gauging stations shows that total sediment load increases in downstream direction, up to the apex of the alluvial fans. Whereas agricultural top soil erosion is most important in the upper parts of the landscape, gully erosion and river bank erosion also contribute much sediment in downstream direction. However, total suspended SY delivered to the lake-based gauging stations is 32 to 53% lower compared to the total suspended SY measured at the gauging station situated near the apex of the alluvial fans. This implies that a significant proportion of the sediment load is buffered by the fans and points to an important dis-connectivity between eroding mountains and rift valley lakes.</p>

scholarly journals Characterization of Water Level Variability of the Main Ethiopian Rift Valley Lakes

Hydrology ◽  
2015 ◽  
Vol 3 (1) ◽  
pp. 1 ◽  
Author(s):  
Mulugeta Belete ◽  
Bernd Diekkrüger ◽  
Jackson Roehrig
Keyword(s):  
Water Level ◽  
Rift Valley ◽  
Ethiopian Rift ◽  
Main Ethiopian Rift ◽  
Rift Valley Lakes

Groundwater-Mediated Response to Holocene Climatic Change Recorded by the Diatom Stratigraphy of an Ethiopian Crater Lake

1999 ◽  
Vol 52 (1) ◽  
pp. 63-75 ◽  
Author(s):  
Richard J. Telford ◽  
Henry F. Lamb
Keyword(s):  
Rift Valley ◽  
Significant Proportion ◽  
Ethiopian Rift ◽  
Crater Lakes ◽  
Groundwater Flux ◽  
Diatom Stratigraphy ◽  
Maar Lake ◽  
Rift Valley Lakes ◽  
Aulacoseira Granulata ◽  
Lake Salinity

The diatom stratigraphy of a 23-m sediment core from Lake Tilo, a maar lake in the Ethiopian Rift Valley, provides a 10,000-yr record of lake salinity and trophic status. Until 5500 14C yr B.P., the phytoplankton was dominated by Aulacoseira granulata, with only minor changes in the abundance of other diatoms; the lake was over 50 m deep, eutrophic, and oligosaline. At 5500 yr B.P., geothermal groundwater inflow, inferred from calcite and silica deposition rates, declined abruptly, and the lake became more oligotrophic, as indicated by a rapid rise in Cyclotella stelligera. About 4500 yr B.P., lake salinity began to increase, reaching approximately its present state ca. 2500 yr B.P., but with a temporary reversal to lower salinity at 4000–3500 yr B.P. The record shows no evidence of salinity increases equivalent to early Holocene low stands of the larger river-fed Rift Valley lakes, probably because of high rates of geothermal groundwater influx. It responded to reduced rainfall at 4500 yr B.P., when levels of the larger lakes also fell, because geothermal groundwater flux had diminished 1000 year earlier, independently of climate. Because geothermal groundwaters can form a significant proportion of a crater lake's hydrological budget and dominate its salinity budget, these results show that variable geothermal groundwater flux can override lake hydrochemical response to climate change. Palaeoclimatic interpretation of palaeosalinity proxies from the sediments of volcanic crater lakes should be approached with caution.

scholarly journals Why are Lake Abaya and Lake Chamo so different? A limnological comparison of two neighboring major Ethiopian Rift Valley lakes

Hydrobiologia ◽  
2018 ◽  
Vol 829 (1) ◽  
pp. 113-124 ◽  
Author(s):  
Fassil E. Teffera ◽  
Pieter Lemmens ◽  
Arne Deriemaecker ◽  
Jozef Deckers ◽  
Hans Bauer ◽  
...  
Keyword(s):  
Rift Valley ◽  
Ethiopian Rift ◽  
Rift Valley Lakes
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