scholarly journals Spatiotemporal Dynamics and Environmental Controlling Factors of the Lake Tana Water Hyacinth in Ethiopia

2020 ◽  
Vol 12 (17) ◽  
pp. 2706
Author(s):  
Abeyou W. Worqlul ◽  
Essayas K. Ayana ◽  
Yihun T. Dile ◽  
Mamaru A. Moges ◽  
Minychl G. Dersseh ◽  
...  
Keyword(s):  
Water Level ◽  
Air Temperature ◽  
Best Management Practices ◽  
Water Hyacinth ◽  
Lake Level ◽  
Management Practices ◽  
Satellite Image ◽  
Spatiotemporal Dynamics ◽  
Lake Tana ◽  
Spatial Coverage

The largest freshwater lake in Ethiopia, Lake Tana, has faced ecological disaster due to water hyacinth (Eichhornia crassipes) infestation. The water hyacinth is a threat not only to the ecology but also to the socioeconomic development of the region and cultural value of the lake, which is registered as a UNESCO reserve. This study aims to map the spatiotemporal dynamics of the water hyacinth using high-resolution PlanetScope satellite images and assesses the major environmental variables that relate to the weed spatial coverage dynamics for the period August 2017 to July 2018. The plausible environmental factors studied affecting the weed dynamics include lake level, water and air temperature, and turbidity. Water temperature and turbidity were estimated from the moderate resolution imaging spectroradiometer (MODIS) satellite image and the water level was estimated using Jason-1 altimetry data while the air temperature was obtained from the nearby meteorological station at Bahir Dar station. The results indicated that water hyacinth coverage was increasing at a rate of 14 ha/day from August to November of 2017. On the other hand, the coverage reduced at a rate of 6 ha/day from December 2017 to June 2018. However, the length of shoreline infestation increased significantly from 4.3 km in August 2017 to 23.4 km in April 2018. Lake level and night-time water temperatures were strongly correlated with water hyacinth spatial coverage (p < 0.05). A drop in the lake water level resulted in a considerable reduction of the infested area, which is also related to decreasing nutrient levels in the water. The water hyacinth expansion dynamics could be altered by treating the nutrient-rich runoff with best management practices along the wetland and in the lake watershed landscape.

scholarly journals Spatial and Temporal Dynamics of Water Hyacinth and Its Linkage with Lake-Level Fluctuation: Lake Tana, a Sub-Humid Region of the Ethiopian Highlands

Water ◽  
2020 ◽  
Vol 12 (5) ◽  
pp. 1435 ◽  
Author(s):  
Minychl G. Dersseh ◽  
Seifu A. Tilahun ◽  
Abeyou W. Worqlul ◽  
Mamaru A. Moges ◽  
Wubneh B. Abebe ◽  
...  
Keyword(s):  
Water Level ◽  
Water Hyacinth ◽  
Lake Level ◽  
Temporal Dynamics ◽  
Water Level Fluctuation ◽  
Suitable Habitat ◽  
Level Fluctuation ◽  
Lake Tana ◽  
Lake Level Fluctuation ◽  
The Impact

Water hyacinth originated from the Amazon Basin and has expanded to other parts of the world since the 1800s. In Ethiopia, the weed is affecting the socio-economic activities of the people whose livelihood is directly or indirectly dependent on Lake Tana. Still, the area covered by water hyacinth and the impact of water level fluctuation on the expansion of water hyacinth has not been known clearly. Therefore, the main objective of this study was to determine the spatiotemporal distribution of water hyacinth and relation with lake-level fluctuation. The area covered by water hyacinth was determined using monthly Sentinel-2 images, which were collected from November 2015 to December 2019. The impact of water level fluctuation on the expansion of water hyacinth was evaluated using hourly water level data converted to a monthly average to correlate with the area covered by the water hyacinth. In addition, MOD13Q1.006 data was used to evaluate the trend of the Normalized Difference Vegetation Index (NDVI) and its linkage with the weed. The maximum areas covered by water hyacinth were 278.3, 613.6, 1108.7, 2036.5, and 2504.5 ha in Feb 2015, October 2016, September 2017, December 2018, and in December 2019, respectively. Its areal coverage was declining from the northern corridors and increasing in eastern shores of the lake. The lake-level fluctuation was observed in the range of 1.5 to 3.98 m in this study. The annual mean maximum spatial values of the NDVI were in the range of 0.27 and 0.47. The area covered by water hyacinth was increasing significantly (P < 0.05) and positively correlated with the seasonal lake-level fluctuation. High water level enabled the expansion of the weed by extending its suitable habitat of shallow water to the flood plain. Based on the results of this study, lake-level fluctuations can have an adverse impact on the expansion of the weed.

scholarly journals Morphological dynamics of gully systems in the subhumid Ethiopian Highlands: the Debre Mawi watershed

SOIL ◽  
2016 ◽  
Vol 2 (3) ◽  
pp. 443-458 ◽  
Author(s):  
Assefa D. Zegeye ◽  
Eddy J. Langendoen ◽  
Cathelijne R. Stoof ◽  
Seifu A. Tilahun ◽  
Dessalegn C. Dagnew ◽  
...  
Keyword(s):  
Best Management Practices ◽  
Management Practices ◽  
Gully Erosion ◽  
Semiarid Region ◽  
Lake Tana ◽  
Ethiopian Highlands ◽  
Best Management ◽  
Humid Region ◽  
Sediment Loss ◽  
Gully Head

Abstract. Gully expansion in the Ethiopian Highlands dissects vital agricultural lands with the eroded materials adversely impacting downstream resources, for example as they accumulate in reservoirs. While gully expansion and rehabilitation have been more extensively researched in the semiarid region of Ethiopia, few studies have been conducted in the (sub)humid region. For that reason, we assessed the severity of gully erosion by measuring the expansion of 13 selected permanent gullies in the subhumid Debre Mawi watershed, 30 km south of Lake Tana, Ethiopia. In addition, the rate of expansion of the entire drainage network in the watershed was determined using 0.5 m resolution aerial imagery from flights in 2005 and 2013. About 0.6 Mt (or 127 t ha−1 yr−1) of soil was lost during this period due to actively expanding gullies. The net gully area in the entire watershed increased more than 4-fold from 4.5 ha in 2005 to 20.4 ha in 2013 (> 3 % of the watershed area), indicating the growing severity of gully erosion and hence land degradation in the watershed. Soil losses were caused by upslope migrating gully heads through a combination of gully head collapse and removal of the failed material by runoff. Collapse of gully banks and retreat of headcuts was most severe in locations where elevated groundwater tables saturated gully heads and banks, destabilizing the soils by decreasing the shear strength. Elevated groundwater tables were therefore the most important cause of gully expansion. Additional factors that strongly relate to bank collapse were the height of the gully head and the size of the drainage area. Soil physical properties (e.g., texture and bulk density) only had minor effects. Conservation practices that address factors controlling erosion are the most effective in protecting gully expansion. These consist of lowering water table and regrading the gully head and sidewalls to reduce the occurrence of gravity-induced mass failures. Planting suitable vegetation on the regraded gully slopes will in addition decrease the risk of bank failure by reducing pore-water pressures and reinforcing the soil. Finally, best management practices that decrease runoff from the catchment will reduce the amount of gully-related sediment loss.

scholarly journals Evaluation of Operation of Lake Tana Reservoir Future Water Use under Emerging Scenario with and without climate Change Impacts, Upper Blue Nile

2005 ◽  
Vol 4 (2) ◽  
pp. 654-663 ◽  
Author(s):  
Getachew Tegegne ◽  
Dr. Ing. Dereje Hailu ◽  
Prof. Dr. S. Moses Aranganathan
Keyword(s):  
Climate Change ◽  
Water Level ◽  
Water Use ◽  
Future Development ◽  
Lake Level ◽  
Climate Change Impacts ◽  
Base Line ◽  
Climate Change Scenarios ◽  
Weap Model ◽  
Lake Tana

This paper presents simulation of Lake Tana reservoir future water use under emerging scenario with and without climate change impacts. Two different development and climate change scenarios were developed to simulate Lake Tana water level i.e., i) Base line scenario (1991-2000) ,ii) Future development scenario on short term periods(2031-2040) , and ii) Future development scenario on long term periods (2091-2100). River head flow estimated by Soil and Water Assessment Tool (SWAT) was used as an input to Water Evaluation And Planning (WEAP) model to simulate the Lake level for each scenario. Based on WEAP model simulation results, demand coverage and reliability of 100% was observed in all scenarios for Tana-Beles hydropower project. For scenarios without climate change impacts, there are longer periods of time when mean monthly lake levels are below 1785 masl (i.e., the minimum lake level required for shipping). Under natural conditions (lake level without project), they exceed this level in 100%.under current conditions (Base line scenario, BLS), they exceed this level in 89% of the months. In the full development scenario (FDSCʹ), this will decrease to 83%. For all scenarios with climate change impacts, Lake water Level will not significantly be affected by climate change impacts.

scholarly journals Modeling on naturalization of inflow and outflow nutrients sources of Blue Nile River at the Lake Tana in Basaltic Plateau of Ethiopia

2020 ◽  
Author(s):  
Asimamaw Nigusie Asitatikie ◽  
Endalkachew Diress Nigussie
Keyword(s):  
Water Balance ◽  
Water Level ◽  
Lake Level ◽  
Maximum Amplitude ◽  
Nile River ◽  
Data Sets ◽  
Regression Analyses ◽  
Lake Tana ◽  
Different Seasons ◽  
Natural Characteristics

Abstract Lake Tana is the largest natural reservoir in Ethiopia and the head water of Abbay basin. However, after building of an irrigation weir and further lying Tunnel to Tana Belles, Lake Tana maximum amplitude of water level canges from 2.18 to 3.56 m that differ substantially in 1.38 m from amplitude of natural water level fluctuation. Understanding the natural characteristics of the Lake is important to know its water balance and for sustainable development. But it is difficult to study the natural characteristics of the Lake and its water balance using the regulated water level and outflow data sets. Thus it is evident that the regulated water level and outflow data sets have to be first naturalized before they are used for any analysis and modeling. Lake level and outflow data that have been collected since 1976 were considered to assess the regulation effect and then for naturalization. Inflows to the Lake from the main tributaries have also been collected to find if there are any correlations with either the Lake Level and/or the outflow. Regression analyses were used to develop the naturalization models. The regression analyses of flows from Gilgel Abay and Gummar with Lake Level shows that there is a very good correlation between them in different seasons. Besides, same has also been observed between Lake Level and out flow. These relationships can be used to naturalize the regulated outflow and water level.

scholarly journals Morphological dynamics of gully systems in the sub-humid Ethiopian Highlands: The Debre Mawi watershed

2016 ◽  
Author(s):  
Assefa Zegeye ◽  
Eddy J. Langendoen ◽  
Cathelijne R. Stoof ◽  
Seifu A. Tilahun ◽  
Dessalegn C. Dagnew ◽  
...  
Keyword(s):  
Best Management Practices ◽  
Management Practices ◽  
Gully Erosion ◽  
Lake Tana ◽  
Ethiopian Highlands ◽  
Best Management ◽  
Humid Region ◽  
Overland Runoff ◽  
Semi Arid Region ◽  
Gully Head

Abstract. Gully expansion in the Ethiopian highlands dissects vital agricultural lands with the eroded materials adversely impacting downstream resources, for example as they accumulate in reservoirs. While gully expansion and rehabilitation have been more extensively researched in the semi-arid region of Ethiopia, few studies have been conducted in the (sub) humid region. For that reason, we assessed the severity of gully erosion and identified gully-forming processes in 13 selected permanent gullies in the sub-humid Debre Mawi watershed, 30 km south of Lake Tana, Ethiopia. In addition, the rate of expansion of the entire drainage network in the watershed was determined using 50 cm resolution aerial imagery flown in 2005 and 2013. More than 0.7 million tons (or 155 t ha−1 yr−1) of soil was lost during this period due to actively expanding gullies. The net gully area in the entire watershed increased more than 4-fold from 4.5 ha in 2005 to 20.4 ha in 2013 (> 3 % of the watershed area), indicating the growing severity of gully erosion and hence land degradation in the watershed. Soil losses were caused by upslope migrating gully heads through a combination of gully head collapse and removal of the failed material by runoff. Collapse of gully banks and retreat of headcuts was most severe in locations where elevated groundwater tables saturated gully head and bank soils, destabilizing the soils by decreasing their shear strength. Elevated groundwater tables were thereby the most important cause of gully expansion. Additional factors that strongly relate to bank collapse were the height of the gully head and the size of the drainage area. Soil physical properties (e.g., texture and bulk density) only had minor effects. Conservation practices that address the most important controlling factors are principally the most effective ways of protecting gully development and expansion. These consist of lowering water table elevation and regrading the gully head and sidewall to reduce the occurrence of gravity-induced mass failures. Planting suitable vegetation on the gully face and around the boundary can also decrease the risk of bank failure by reducing pore-water pressures and reinforcing the soil. Best management practices affecting the runoff contributing catchment may decrease the overland runoff-induced gully head erosion.

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