scholarly journals Surface and subsurface flow effect on permanent gully formation and upland erosion near Lake Tana in the northern highlands of Ethiopia

2010 ◽  
Vol 14 (11) ◽  
pp. 2207-2217 ◽  
Author(s):  
T. Y. Tebebu ◽  
A. Z. Abiy ◽  
A. D. Zegeye ◽  
H. E. Dahlke ◽  
Z. M. Easton ◽  
...  
Keyword(s):  
Water Table ◽  
Gully Erosion ◽  
Grazing Land ◽  
Cross Sectional ◽  
Lake Tana ◽  
Erosion Rates ◽  
Remotely Sensed Imagery ◽  
Reservoir Siltation ◽  
Upland Erosion ◽  
Elevated Water

Abstract. Gully formation in the Ethiopian Highlands has been identified as a major source of sediment in water bodies, and results in sever land degradation. Loss of soil from gully erosion reduces agricultural productivity and grazing land availability, and is one of the major causes of reservoir siltation in the Nile Basin. This study was conducted in the 523 ha Debre-Mawi watershed south of Bahir Dar, Ethiopia, where gullies are actively forming in the landscape. Historic gully development in a section of the Debre-Mawi watershed was estimated with semi structured farmer interviews, remotely sensed imagery, and measurements of current gully volumes. Gully formation was assessed by instrumenting the gully and surrounding area to measure water table levels and soil physical properties. Gully formation began in the late 1980's following the removal of indigenous vegetation, leading to an increase in surface and subsurface runoff from the hillsides. A comparison of the gully area, estimated from a 0.58 m resolution QuickBird image, with the current gully area mapped with a GPS, indicated that the total eroded area of the gully increased from 0.65 ha in 2005 to 1.0 ha in 2007 and 1.43 ha in 2008. The gully erosion rate, calculated from cross-sectional transect measurements, between 2007 and 2008 was 530 t ha−1 yr−1 in the 17.4 ha area contributing to the gully, equivalent to over 4 cm soil loss over the contributing area. As a comparison, we also measured rill and interrill erosion rates in a nearby section of the watershed, gully erosion rates were approximately 20 times the measured rill and interrill rates. Depths to the water table measured with piezometers showed that in the actively eroding sections of the gully the water table was above the gully bottom and, in stable gully sections the water table was below the gully bottom during the rainy season. The elevated water table appears to facilitate the slumping of gully walls, which causes the gully to widen and to migrate up the hillside.

scholarly journals Surface and subsurface flow effect on permanent gully formation and upland erosion near Lake Tana in the Northern Highlands of Ethiopia

2010 ◽  
Vol 7 (4) ◽  
pp. 5235-5265 ◽  
Author(s):  
T. Y. Tebebu ◽  
A. Z. Abiy ◽  
H. E. Dahlke ◽  
Z. M. Easton ◽  
A. D. Zegeye ◽  
...  
Keyword(s):  
Water Table ◽  
Crop Yields ◽  
Gully Erosion ◽  
Rill Erosion ◽  
Grazing Land ◽  
Lake Tana ◽  
Erosion Rates ◽  
Reservoir Siltation ◽  
Upland Erosion ◽  
Elevated Water

Abstract. Gully formation in the Ethiopian Highlands has been identified as a major source of sediment in water bodies, and results in sever land degradation. Loss of soil from gully erosion lowers crop yields, reduces grazing land availability, and is one of the major causes of reservoir siltation in the Nile Basin. This study was conducted in the 523 ha of Debre-Mawi watershed south of Bahir Dar, Ethiopia, where gullies are actively forming in the landscape. Historic gully development in a section of the Debre-Mawi watershed was estimated with semi structured farmer interviews, remotely sensed imagery, and estimates of current gully volumes. Gully formation was assessed by instrumenting the gully and surrounding area to measure water table levels and soil physical properties. Gully formation began in the 1980's following the removal of indigenous vegetation, leading to an increase in surface and subsurface runoff from the hillsides. A comparison of the gully area, estimated from a 0.58 m resolution quick bird image, with the current gully area mapped with a GPS, indicated that the total eroded area of the gully increased from 0.65 ha in 2005 to 1.0 ha in 2007 and 1.43 ha in 2008. The gully erosion rate between 2007 and 2008 was 530 t ha-1yr-1 in the 17.4 ha area contributing to the gully, equivalent to over 4 cm soil loss over the contributing area. As a comparison, we also measured rill and inter-rill erosion rates in a nearby section of the watershed, gully erosion rates were approximately 20 times the measured rill and inter rill rates. Depths to the water table measured with piezometers showed that in the actively eroding sections of the gully the water table was above the gully bottom and, in stable gully sections the water table was below the gully bottom during the rainy season. The elevated water table facilitates the slumping of gully walls, which causes widening and up-migration on the hillside.

The effects of a permanently elevated water table in an acid sulphate soil on reed canary grass for combustion

2013 ◽  
Vol 375 (1-2) ◽  
pp. 149-158 ◽  
Author(s):  
Kenedy E. Epie ◽  
Seija Virtanen ◽  
Arja Santanen ◽  
Asko Simojoki ◽  
Frederick L. Stoddard
Keyword(s):  
Water Table ◽  
Reed Canary Grass ◽  
Acid Sulphate Soil ◽  
Acid Sulphate ◽  
Elevated Water Table ◽  
Canary Grass ◽  
Elevated Water

scholarly journals Estimation of soil loss using remote sensing and GIS-based universal soil loss equation in northern catchment of Lake Tana Sub-basin, Upper Blue Nile Basin, Northwest Ethiopia

2020 ◽  
Vol 9 (1) ◽  
Author(s):  
Veera Narayana Balabathina ◽  
R. P. Raju ◽  
Wuletaw Mulualem ◽  
Gedefaw Tadele
Keyword(s):  
Remote Sensing ◽  
Land Use ◽  
Soil Erosion ◽  
Soil Loss ◽  
Erosion Rate ◽  
Soil Erodibility ◽  
Lake Tana ◽  
Erosion Rates ◽  
Soil Erosion Rate ◽  
Soil Loss Equation

Abstract Background Soil erosion is one of the major environmental challenges and has a significant impact on potential land productivity and food security in many highland regions of Ethiopia. Quantifying and identifying the spatial patterns of soil erosion is important for management. The present study aims to estimate soil erosion by water in the Northern catchment of Lake Tana basin in the NW highlands of Ethiopia. The estimations are based on available data through the application of the Universal Soil Loss Equation integrated with Geographic Information System and remote sensing technologies. The study further explored the effects of land use and land cover, topography, soil erodibility, and drainage density on soil erosion rate in the catchment. Results The total estimated soil loss in the catchment was 1,705,370 tons per year and the mean erosion rate was 37.89 t ha−1 year−1, with a standard deviation of 59.2 t ha−1 year−1. The average annual soil erosion rare for the sub-catchments Derma, Megech, Gumara, Garno, and Gabi Kura were estimated at 46.8, 40.9, 30.9, 30.0, and 29.7 t ha−1 year−1, respectively. Based on estimated erosion rates in the catchment, the grid cells were divided into five different erosion severity classes: very low, low, moderate, high and extreme. The soil erosion severity map showed about 58.9% of the area was in very low erosion potential (0–1 t ha−1 year−1) that contributes only 1.1% of the total soil loss, while 12.4% of the areas (36,617 ha) were in high and extreme erosion potential with erosion rates of 10 t ha−1 year−1 or more that contributed about 82.1% of the total soil loss in the catchment which should be a high priority. Areas with high to extreme erosion severity classes were mostly found in Megech, Gumero and Garno sub-catchments. Results of Multiple linear regression analysis showed a relationship between soil erosion rate (A) and USLE factors that soil erosion rate was most sensitive to the topographic factor (LS) followed by the support practice (P), soil erodibility (K), crop management (C) and rainfall erosivity factor (R). Barenland showed the most severe erosion, followed by croplands and plantation forests in the catchment. Conclusions Use of the erosion severity classes coupled with various individual factors can help to understand the primary processes affecting erosion and spatial patterns in the catchment. This could be used for the site-specific implementation of effective soil conservation practices and land use plans targeted in erosion-prone locations to control soil erosion.

Rapid morphological evolution during beach breaching and closure at a bar-built estuary

2021 ◽  
Author(s):  
Mara Orescanin ◽  
Tyonna McPherson ◽  
Paul Jessen
Keyword(s):  
Sediment Transport ◽  
River Discharge ◽  
Morphological Evolution ◽  
Water Levels ◽  
Low Flow ◽  
Long Term Stability ◽  
Erosion Rates ◽  
Discharge Rates ◽  
Elevation Changes ◽  
Elevated Water

<p>The Carmel River runs 58 km from the Santa Lucia Mountains through the Carmel Valley eventually entering a lagoon at Carmel River State Beach near Carmel, California, USA. During the dry summer months, the lagoon is closed, with no connection to the coastal ocean.  However, during the wet winter months, the river often breaches through the lagoon allowing water to freely flow between the river and Carmel Bay. Sediment transport, in part owing to river discharge and in part owing to ocean forcing (tides and waves), contributes heavily to whether the lagoon is open or closed: when there are low flow conditions, waves and tides can decrease flow rates in the breach, allowing sediment to settle. The sediment budget is expected to be a closed system, owing to the rocky headlands and long-term stability (no yearly regression or transgression) of the shoreline, despite managed attempts to control breach and closure timing. However, it is currently unknown 1) how velocity profiles evolve during breaching, and 2) how much sediment moves during such an event. The hypothesis is that the breach mouth can completely disappear and re-emerge over a single breach-closure cycle, leading to meter-scale daily accretion and erosion rates of berm height if berm elevation is significantly lower than the expected steady-state berm height. Furthermore, it is hypothesized that during active breaching, discharge rates through the breach channel are larger than upstream river discharge rates owing to elevated water levels within the back lagoon. This study uses a RiverSurveyor M9 Acoustic Doppler Profiler to measure outflow discharge and GPS topographic surveys to quantify elevation changes. A velocity profile can be built which will estimate the sediment transport potential within the breach. The information obtained will help identify and better understand the river discharge thresholds which contribute to frequent breaching as well as estimates of morphological evolution during breaching, which are currently unknown, and can assist in determining likelihood of successful managed breaching and closure events. </p>

scholarly journals Reconstructing long-term gully dynamics in Mediterranean agricultural areas

2017 ◽  
Vol 21 (1) ◽  
pp. 235-249 ◽  
Author(s):  
Antonio Hayas ◽  
Tom Vanwalleghem ◽  
Ana Laguna ◽  
Adolfo Peña ◽  
Juan V. Giráldez
Keyword(s):  
Land Use ◽  
Temporal Resolution ◽  
Land Use Changes ◽  
Mediterranean Area ◽  
Gully Erosion ◽  
Aerial Photographs ◽  
High Temporal Resolution ◽  
Erosion Rates ◽  
Erosion Processes

Abstract. Gully erosion is an important erosive process in Mediterranean basins. However, the long-term dynamics of gully networks and the variations in sediment production in gullies are not well known. Available studies are often conducted only over a few years, while many gully networks form, grow, and change in response to environmental and land use or management changes over a long period. In order to clarify the effect of these changes, it is important to analyse the evolution of the gully network with a high temporal resolution. This study aims at analysing gully morphodynamics over a long timescale (1956–2013) in a large Mediterranean area in order to quantify gully erosion processes and their contribution to overall sediment dynamics. A gully network of 20 km2 located in southwestern Spain has been analysed using a sequence of 10 aerial photographs in the period 1956–2013. The extension of the gully network both increased and decreased in the study period. Gully drainage density varied between 1.93 km km−2 in 1956, a minimum of 1.37 km km−2 in 1980, and a maximum of 5.40 km km−2 in 2013. The main controlling factor of gully activity appeared to be rainfall. Land use changes were found to have only a secondary effect. A new Monte Carlo-based approach was proposed to reconstruct gully erosion rates from orthophotos. Gully erosion rates were found to be relatively stable between 1956 and 2009, with a mean value of 11.2 t ha−1 yr−1. In the period 2009–2011, characterized by severe winter rainfalls, this value increased significantly to 591 t ha−1 yr−1. These results show that gully erosion rates are highly variable and that a simple interpolation between the starting and ending dates greatly underestimates gully contribution during certain years, such as, for example, between 2009 and 2011. This illustrates the importance of the methodology applied using a high temporal resolution of orthophotos.

Preventing Acid Mine Drainage with an Elevated Water Table: Long-Term Column Experiments and Parameter Analysis

2010 ◽  
Vol 213 (1-4) ◽  
pp. 437-458 ◽  
Author(s):  
Mariam Ouangrawa ◽  
Michel Aubertin ◽  
John W. Molson ◽  
Bruno Bussière ◽  
Gérald J. Zagury
Keyword(s):  
Acid Mine Drainage ◽  
Water Table ◽  
Mine Drainage ◽  
Parameter Analysis ◽  
Column Experiments ◽  
Acid Mine ◽  
Elevated Water Table ◽  
Elevated Water

Small permanent gullies: modelling and application to a semiarid region

2020 ◽  
Author(s):  
Pedro Henrique Lima Alencar ◽  
José Carlos de Araújo ◽  
Adunias dos Santos Teixeira
Keyword(s):  
Water Table ◽  
Cross Sections ◽  
Land Degradation ◽  
Gully Erosion ◽  
Drainage Area ◽  
Semiarid Region ◽  
Country Road ◽  
Brazilian Semiarid ◽  
Key Drivers ◽  
Shallow Soils

<p>Gullies are key drivers of land degradation, are important sources of sediment and increase sediment and pollutant connectivity in the catchment. They also play an important role in desertification areas, changing the water-table height and in farmlands, reducing productive areas. In this study, we attempted to model small permanent gullies, common in the Brazilian Semiarid Region, where the shallow soils limit the size of gullies cross-sections to a depth of no more than one meter. To model this process, we coupled the models of Foster and Lane (1983) and Sidorchuk (1999), in order to consider the effect of permanent gullies not considered in the first. Both models need as input the discharge peak and its duration, however, these data are frequently not available. We tested four different rain intensities (average, 60-minute, 30-minute and 15-minute), finding that the most intense 30 minutes represent the best the effects of the storms over gully erosion. The coupling of the two models is defined by a threshold that indicates when the equations for sidewall erosion proposed by Sidorchuk should be applied. To validate the model, we measured three gullies in the Brazilian Semiarid Region. The gullies were initiated in 1958 after the construction of a country road and have drainage area below 1 ha. The model yielded a Nash-Sutcliffe coefficient of 0.85.</p>

scholarly journals Gully erosion in Northeast China -- a case study on history, erosion rates and causes

2021 ◽  
Author(s):  
Yanru WEN ◽  
Till Kasielke ◽  
Hao Li ◽  
Harald Zepp ◽  
Bin Zhang
Keyword(s):  
Northeast China ◽  
Arable Land ◽  
Gully Erosion ◽  
Study Region ◽  
Erosion Rates ◽  
Erosion History ◽  
Aerial Vehicle ◽  
Agricultural Use ◽  
Steep Slopes ◽  
Gully Density

Mollisols are of major importance for food security worldwide but are increasingly degraded by soil erosion. Mollisols in Northeast China have been converted into agricultural use only recently, but gullies are widely distributed and gully erosion history, rates and causes remained unclear. We chose a study typical village to estimate initiation years and development rates of the gully systems from 1968 to 2018 by using aerial and satellite imagery. The outlet fan deposits of a large gully system were dated by Caesium-137 (137Cs) and artefacts. To verify the results, we collected information from local farmers. Gully volumes were measured by structure-from-motion technique using photos taken from an unmanned aerial vehicle. Our results showed that gully systems had already appeared on the steep slopes and along unpaved roads in 1968 and had become more complex by 2018 despite terracing and afforestation. Based on gully morphology and 137Cs, gully erosion was estimated to have started in the 1950s to 1960s when the original grassland and forest were completely converted into arable land. From 1968 to 2018, the gully density increased from 1.2 to 2.3 km km-2. The gully heads retreated at speeds from 1.5 to 2.5 m yr-1, and the soil loss from gully erosion ranged from 25.7 to 44.7 Mg yr-1 ha-1. These data demonstrate the severity of gully erosion in study region and underline the importance of appropriate countermeasures, such as maintenance of abandoned terraces under reforested land and better design and construction of roads within the arable land.

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