Farming systems in Lake Tana basin, Ethiopia: Land surface management and its impact on runoff response
- JanNyssen
- EnyewAdgo
- MeketeDessie
Afwatering van de akkers in Ethiopië, een vloek of zegen?
Van jongs af aan staan kinderen in Ethiopië al mee op het veld met hun vader om de akkers te bewerken. De manier waarop hij dit doet, heeft hij geleerd van zijn vader die het op zijn beurt ook heeft geleerd van zijn vader enz. Zo worden akkers op grote schaal afgewaterd, waarbij de techniek gebaseerd is op duizenden jaren akkerbouw met de ploeg. Echter is deze techniek weinig omschreven, laat staan geanalyseerd. We nemen jullie mee in onze zoektocht naar het gebruik van drainagevoren, en de gevolgen ervan.
Wanzaye, een plaats van contrasten
Voor het onderzoek, uitgevoerd in samenwerking met de Bahir Dar University en een VLIR project, hadden we ons geen geschiktere omgeving dan Wanzaye kunnen inbeelden. Gelegen in Noord- Ethiopië, aan de voet van de hellingen rond het grootste meer van Ethiopië (Tanameer, ongeveer drieduizend km²) bevinden we ons in een tropisch bergklimaat met een lang droogseizoen en een regenseizoen van juni tot september. De vulkanische voorgeschiedenis van het gebied maakt dat de bodem hier enorm vruchtbaar is. Daarnaast omhelst het Tanabekken een gebied dat zich leent tot energieproductie door middel van waterkrachtcentrales, visvangst en toerisme, en dat een enorme biodiversiteit bezit.
Wanzaye telt ongeveer 500 uiterst gastvrije inwoners die leven van hun landbouwopbrengsten en kleinschalige handel. Dit maakt dat ze zeer kwetsbaar zijn voor de onvoorspelbaarheid van de neerslag, bevolkingsgroei en landdegradatie. Landbouwers zien hun bodems afspoelen en ravijnen groeien doorheen het regenseizoen. Drie verschillende landbeheersystemen worden in Wanzaye en omgeving door de landbouwers toegepast op hun akkertjes, afhankelijk van hun visie op de impact op bodemerosie: (1) een meter hoge stenen muurtjes die leiden tot terrasvorming, (2) een eeuwenoude techniek van drainagevoortjes (feses) en (3) een combinatie van beide.
Terrasmuurtjes en/of drainagevoren
Stenen muurtjes zorgen ervoor dat geërodeerde bodemdeeltjes niet met het afstromende regenwater worden afgevoerd maar worden vastgehouden op het akkerland. Het maken ervan is een zeer arbeidsintensieve karwij die wordt georganiseerd door de overheid (Ministerie van Landbouw) als gemeenschapswerk. De landbouwers zijn het er unaniem over eens dat de bouw van terrasmuurtjes de beste manier is om landdegradatie te beperken.
Tijdens het regenseizoen trekken de boeren met hun ossenspan schuin hellende drainagevoortjes (feses) om het teveel aan water weg te draineren (zie figuur). In Wanzaye zijn zulke voortjes gemiddeld 27 cm breed en 12 cm diep. Het gebruik van artificiële afwatering heeft vele voordelen voor een akkerland: het vermindert de bodemcompactie, het bevordert luchtcirculatie door de bodem en ook de wortelzone is dieper. Daarnaast worden drainagevoortjes ook als bodemconserveringsmaatregel toegepast om ongecontroleerde waterstromen over het akkerland te vermijden. Desalniettemin wordt artificiële drainage vaak als een slechte praktijk aanzien, omdat de geconcentreerde stroom zowel op het akkerland als stroomafwaarts gaat leiden tot insnijding. Kortom, wetenschappers hebben tot nog toe weinig consensus bereikt over de finale balans van de positieve en negatieve effecten van drainagevoren.
Landdegradatie verder hellingafwaarts
Om een idee te krijgen van de mate van stroomafwaartse erosie in relatie tot de drie verschillende landbouwtechnieken werd er gebruik gemaakt van topografische drempelwaardes voor ravijnontwikkeling. Die topografische drempelwaardes worden bepaald aan het ravijnhoofd, rekening houdende de hellingshoek en met het de oppervlakte van het bekken. Neerslag die afstroomt over het akkerland (runoff), zal stroomafwaarts niet tot ravijnerosie leiden als de topografische condities (hellingshoek en oppervlakte van het bekken) klein genoeg zijn, d.w.z. onder de drempelwaardes liggen voor een specifiek landbeheersysteem. We onderzochten hoe deze drempelwaardes voor de drie verschillende landbeheersystemen in relatie tot elkaar staan.
Bijgestaan door een lokale vertaler en het gebruik van een GPS werden 75 bekkens afgebakend, waarvan 26 met enkel gebruik van feses, 27 met enkel gebruik van stenen muurtjes (terrasbekkens) en 22 waar zowel terrasmuurtjes als feses werden aangewend. Aan de hand van een digitaal hoogtemodel werden de topografische factoren berekend en uitgezet op een grafiek. Hieruit bleek dat de drempelwaarde het hoogst ligt voor terrasbekkens en het laagst voor fesesbekkens wat betekent dat die laatsten het gevoeligst zijn voor de ontwikkeling van ravijnen. Tot nog toe werd deze analyse enkel toegepast om verschillende landgebruiken (bos, weiland, akkerland…) met elkaar te vergelijken, maar niet de beheertechnieken op de akkers zelf.
Erosie op het akkerland
Op terrein ondervonden we dat naast de stroomafwaartse erosie, ook de landdegradatie op het akkerland zelf niet te verwaarlozen was. Echter staat internationaal onderzoek rond dit fenomeen nog in zijn kinderschoenen. Metingen in Wanzaye toonden dat on-site geulerosie in 41% van de gevallen veroorzaakt was door een slechte werking van feses, terwijl slechts 16% veroorzaakt was door een slechte constructie van terrasmuurtjes. Daarnaast werd ook een positieve correlatie gevonden tussen het totaal volume geulerosie en de densiteit van de voortjes, en een negatieve in relatie tot de densiteit van de stenen muurtjes. Een ander gegeven dat de bevindingen ondersteunt, vonden we terug in de debieten die op twaalf plaatsen werden opgemeten door medewerkers. We stelden een positieve relatie vast tussen de densiteit van de voortjes en de debieten van het afstromende water waardoor er meer erosie kan plaatsvinden (ten gevolge van grotere kracht van het water) in de drainagevoortjes bij een hogere feses densiteit.
Als nuance bij bovenstaande bevindingen komt nog dat feses in het studiegebied worden gemaakt met een hellingshoek die kleiner is dan de helling van het akkerland. Hierdoor zal het water minder snel stromen door de feses dan bij rechtstreeks afstromen over het land en dus ook minder bodemerosie veroorzaken.
Naar een finale balans ?
We hebben bevestigd dat het gebruik van terrasmuurtjes een positief effect heeft bij het streven naar een verminderde landdegradatie. Voor het gebruik van traditionele drainagevoren is het resultaat echter minder eenduidig. We vonden zowel bewijzen die aantoonden dat dit erosie in de hand werkt als aanwijzingen van verminderde landdegradatie. Onze zoektocht eindigt hier dus niet, en het totale plaatje van het gebruik van drainagevoren moet verder aangevuld worden waarbij moderne wetenschap toelaat om verbeteringen te suggereren.
Bibliografie
Achten, W.M.J., Dondeyne, S., Mugogo, S., Kafiriti, E., Poesen, J., Deckers, J., Muys, B. (2008) “Gully erosion in South Eastern Tanzania: spatial distribution and topographic thresholds”. Zeitschrift für Geomorphology. 52 (2), 225-235.
Alt, S., Jenkins, A., Lines, K.R. (2009) Saving soil- A Landholder’s Guide to Preventing and Repairing Soil Erosion. New South Wales: NSW Department of Primary Industry.
Amsalu, A., de Graaf, J. (2007) “Determinants of adoption and continued use of stone terraces for soil and water conservation in an Ethiopian highland watershed”. Ecological Economics. 61 (2-3), 294-302.
Aquastat (2005) Country Profiles: Ethiopia. Water Report 29, FAO.
Araya, A., Stroosnijder, L. (2010) “Effects of tied ridges and mulch on barley (Hordeum vulgare) rainwater use efficiency and production in Northern Ethiopia”. Agricultural Water Management. 97 (6), 841-847.
Araya, T., Cornelis, W.M., Nyssen, J., Govaerts, B., Bauer, H., Gebreegziabher, T., Oicha, T., Raes, D., Sayre, K.D., Haile, M., Deckers, J. (2011) “Effects of conservation agriculture on runoff, soil loss and crop yield under rainfed conditions in Tigray, Northern Ethiopia”. Soil Use and Management. 27 (3), 404-414.
Araya, T., Cornelis, W.M., Nyssen, J., Govaerts, B., Getnet, F., Bauer, H., Amare, K., Raes, D., Haile, M., Deckers, J. (2012) “Medium-term effects of conservation agriculture based cropping systems for sustainable soil and water management and crop productivity in the Ethiopian Highlands”. Field Crops Research. 132, 53-62.
Arcement, G.J., Schneider, V.R. (1989) Guide for Selecting Manning's Roughness Coefficients for Natural Channels and Flood Plains. U.S. Geological Survey Water-Supply Paper 2339. U.S. Department of Transportation. Federal Highway Administration.
Archibold, O.W., Levesque, L.M.J., de Boer, D.H., Aitken, A.E., Delanoy, L. (2003) “Gully retreat in a semi-urban catchment in Saskatoon, Saskatchewan”. Applied Geography. 23 (4), 261-279.
Ashagre, B.B. (2009) Formulation of Best Management Option For a Watershed Using Swat (Anjeni watershed, Blue Nile Basin, Ethiopia). Unpublished Thesis. Cornell University, Ithaca, NY, USA.
Astatke, A., Jabar, M., Mohamed-Saleem, M.A., Erkossa, T. (2002) “Development and testing of low cost animal drawn minimum tillage implements: experience on Vertisols in Ethiopia”. Agricultural Mechanization in Asia, Africa, and Latin America. 33 (2), 9-14.
Auzet, A.V., Boiffin, J., Papy, F., Ludwig, B., Maucorp, J. (1993) “Rill erosion as a function of the characteristics of cultivated catchments in the North of France”. Catena. 20 (1-2), 41–62.
Awulachew, S.B., McCartney, M., Steenhuis, T.S., Ahmed, A.A. (2008) A Review of Hydrology, Sediment and Water Resource Use in the Blue Nile Basin. Colombo, Sri Lanka: International Water Management Institute. IWMI Working Paper 131.
Awulachew, S.B., Ahmed, A.A., Haileselassie, A., Yilma, A.D., Bashar, K.E., McCartney, M., Steenhuis, T. (2010) Improved Water and Land Management in the Ethiopian Highlands and its Impact on Downstream Stakeholders Dependent on the Blue Nile. CGIAR Challenge Program on Water and Food.
Bankoff, G. (2013) “The 'English Lowlands' and the North Sea basin system: A history of shared risk”. Environment and History. 19 (1), 3-37.
Barnes, H.H. (1967) Roughness Characteristics of Natural Channels. U.S. Geological Survey Water-Supply Paper. Washington, D.C.: U.S. Government Printing Office.
Barthès, B., Roose, E. (2002) “Aggregate stability as an indicator of soil susceptibility to runoff and erosion; validation at several levels”. Catena. 47 (2), 133-149.
Baruah, T.C., Barthakur, H.P. (1997) A Textbook of Soil Analysis. Vikas, New Delhi.
Bates, P.D., Anderson, M.D., Price, D., Hardy, R. and Smith C. (1996) “Analysis and development of hydraulic models for flood plain flow”. In: Anderson, M.G., Walling, D.E., Bates, P.D. (Eds.) Flood Plain Processes. Chichester: Wiley & Sons. pp. 215-254.
Bayabil, H.K., Tilahun, S.A., Collick, A.S., Yitaferu, B., Steenhuis, T.S. (2010) “Are runoff processes ecologically or topographically driven in the (sub) humid Ethiopian highlands? The case of the Maybar watershed”. Ecohydrology. 3 (4), 457-466.
Begin, Z.B., Schumm, S.A. (1979) “Instability of Alluvial Valley Floors - Method for Its Assessment”. Transactions of the ASAE. 22 (2), 347-350.
Ben-Hur, M., Shainberg, I., Bakker, D., Keren, R. (1985) "Effect of soil texture and CaCO3 content on water infiltration in crusted soil as related to water salinity". Irrigation Science. 6 (4), 281-294.
Bennett, H.H. (1939) Soil Conservation. New York: Agro-Bios.
Bennet, S.J., Casali, J., Robinson, K.M., Kadavy, K.C. (2000) “Characteristics of actively eroding ephemeral gullies in an experimental channel”. Transactions of the ASAE. 43 (3), 641–649.
Berndt, R.D., Coughlan, K.J. (1977) “The nature of changes in bulk density with water content in a cracking clay”. Australian Journal of Soil Research. 15 (1), 27-37.
Beuselinck, L., Govers, G., Poesen, J., Degraer, G. (1998) "Grain-size analysis by laser diffractometry: comparison with the sieve-pipette method". Catena. 32 (3-4), 193-208.
Bewket, W., Sterk, G. (2003) “Assessment of soil erosion in cultivated fields using a survey methodology for rills in the Chemoga watershed”. Agriculture Ecosystems & Environment. 97 (1-3), 81-93.
Biazin, B., Stroosnijder, L., Temesgen, M., Abdul Kedir, A., Sterk, G. (2011) “The effect of long-term maresha ploughing on soil physical properties in the Central Rift Valley of Ethiopia”. Soil & Tillage Research. 111 (2), 115-122.
Billi, P., Dramis, F. (2003) “Geomorphological investigation on gully erosion in the Rift Valley and the northern highlands of Ethiopia”. Catena. 50 (2-4), 353-368.
Blaikie, P., Brookfield, H.C., Allen, B. (1994) Land Degradation and Society. London: Routledge.
Bonilla, C.A., Johnson, O.I. (2012) "Soil erodibility mapping and its correlation with soil properties in Central Chile". Geoderma. 189-190, 116-123.
Bouyoucos, G.J. (1935) “The clay ratio as a criterion of susceptibility of soils to erosion”. Journal of the American Society of Agronomy. 27, 738-741.
Bragg, O.M. (2002) “Hydrology of peat-forming wetlands in Scotland”. Science of the Total Environment. 294 (1-3), 111-129.
Brenner, C., Strohmeier, S., Ziadat, F., Klik, A. (2013) Soil Conservation Measures in the Ethiopian Highlands: The Effectiveness of Stone Bunds on Soil Erosion Processes. Paper presented at the EGU General Assembly 2013, Vienna, Austria. Geophysical Research Abstracts, Vol. 15, EGU2013-5392-3.
Brubaker, S.C., Holzhey, C.S., Brasher, B.R. (1992) "Estimating the water-dispersible clay content of soils". Alliance of Crop, Soil, and Environmental Science Societies. 55 (4), 1226-1232.
Burkard, M.B., Kostachuk, R.A. (1995) “Initiation and evolution of gullies along the shoreline of Lake Huron”. Geomorphology. 14, 211–219.
Carter, M.R. (1990) "Relative measures of soil bulk density to characterize compaction in tillage studies on fine sandy loam". Canadian Journal of Soil Sciences. 70 (3), 425-433.
Casali, J., Lopez, J.J., Giraldez, J.V. (1999) “Ephemeral gully erosion in southern Navarra (Spain)”. Catena. 36 (1-2), 65-84.
Chiu, C., Said, C. (1995) “Maximum and mean velocities and entropy in open-channel flow”. Journal of Hydraulic Engineering. 121 (1), 26–35.
Chorley, R.J., Morgan, M.A. (1962) “Comparison of morphometric features, Unaka Mountains, Tennessee and North Carolina, and Dartmoor, England”. Geologogical Society of America Bulletin. 73 (1), 17-34.
Chow,V.T. (1959) Open-Channel Hydraulics. New York: McGraw-Hill Book Co.
Colot, C. (2012) Soil-landscape Relation at Regional Scale in Lake Tana Basin (Ethiopia). Unpublished thesis. KULeuven: Department of Soil and Water Management.
Conway, D. (2000) “The climate and hydrology of the Upper Blue Nile River”. The Geographical Journal. 166 (1), 49-62.
Coon, W.F. (1995) Estimates of Roughness Coefficients for Selected Nztural Stream Channels with Vegetated Banks in New York. New York: New York State Department of Transportation. U.S. Geological Survey Open-File Report 93-161. Ithaca.
Costa, J.E., O’Connor, J.E. (2013) “Geomorphically effective floods”. In: Costa, J.E., Miller, A.J., Potter, K.W., Wilcock, P.R. (Eds.) Natural and Anthropogenic Influences in Fluvial Geomorphology. Washington: American Geophysical Union.
Cowan, W.I. (1956) “Estimating hydraulic roughness coefficients”. Agricultural Engineering. 37 (7), 473-475.
Dargahi, B., Setegn, S.G. (2011) “Combined 3D hydrodynamic and watershed modeling of Lake Tana, Ethiopia”. Journal of Hydrology. 398 (1-2), 44-64.
Deckers, J.A., Nachtergaele, F.O., Spaargaren, O.C. (Eds.) (1998). World Reference Base for Soil Resource: Introduction. Acco Leuven/Amersfoort. Belgium.
Descheemaeker, K., Nyssen, J., Poesen, J., Raes, D., Haile, M., Muys, B., Deckers, S. (2006) “Runoff on slopes with restoring vegetation: A case study from the Tigray highlands, Ethiopia”. Journal of Hydrology. 331 (1-2), 219-241.
Descheemaeker, K., Poesen, J., Borselli, L., Nyssen, J., Raes, D., Haile, M., Muys, B., Deckers, J. (2008) “Runoff curve numbers for steep hillslopes with natural vegetation in semi-arid tropical highlands, northern Ethiopia”. Hydrological Processes. 22 (20), 4097-4105.
Dessie, M., Verhoest, N.E., Admasu, T., Pauwels, V.R., Poesen, J., Adgo, E., DEckers, J., Nyssen, J. (2014) “Effects of the floodplain on river discharge into Lake Tana (Ethiopia)”. Journal of Hydrology. submitted.
Dickhudt, P.J., Friedrichs, C.T., Sanford, L.P. (2011) "Mud matrix solids fraction and bed erodibility in the York River estuary, USA, and other muddy environments". Continental Shelf Research. 31 (10), S3-S13.
Dile, Y.T., Raghavan, S. (2014) “Evaluation of CFSR climate data for hydrologic prediction in data-scarce watersheds: an application in the Blue Nile River Basin”. Journal of the American Water Resources Association. 1-16.
Driessen, P., Deckers, J., Spaargaren, O., Nachtergaele, F. (2001) Lecture Notes on the Major Soils of the World. Rome: Food and Agricultural Organization of the United Nations.
Dunaway, D., Swanson, S.R., Wendel, J., Clary, W. (1994) "The effect of herbaceous plant-communities and soil textures on particle erosion of alluvial streambanks". Geomorphology. 9 (1), 47-56.
Easton, Z.M., Fuka, D.R., White, E.D., Collick, A.S., Ashagre, B.B., McCartney, M., Awulachew, S.B., Ahmed, A.A., Steenhuis, T.S. (2010) “A multi basin SWAT model analysis of runoff and sedimentation in the Blue Nile, Ethiopia”. Hydrology and Earth System Sciences. 14 (10), 1827-1841.
Engida, A.N. (2010) Modelisation Hydrosedimentaire dans le Basin Versant du Lac Tana en Ethiopie. PhD dissertation. Université de Grenoble : spécialité Terre, Univers, Environnement.
Erkossa, T., Stahr, K., Gaiser, T. (2005) “Effect of different methods of land preparation on runoff, soil and nutrient losses from a Vertisol in the Ethiopian highlands”. Soil Use and Management. 21 (2), 253-259.
Fares, A., Buss, P., Dalton, M., El-Kadi, A.I., Parsons, L.R. (2004) "Dual field calibration of capacitance and neutron soil water sensors in a shrinking-swelling clay soil". Vadose Zone Journal. 3 (4), 1390-1399.
FAO (2007) Guidelines and Computer Programs for the Planning and Design of Land Drainage Systems. Irrigation and Drainage Paper, Volume 62. Food and Agriculture Organization of the United Nations, Rome (233 pages).
FAO (2012) Peatlands. Guidance for Climate Change Mitigation Through Conservation, Rehabilitation and Sustainable Use. Mitigation of Climate Change in Agriculture Programme. Food and Agriculture Organization of the United Nations, Rome (114 pages).
Feleke, A. (1987) “Effect of vegetative cover, tillage and planting system on run-off, soil erosion and other soil physical properties”. Agricultural Mechanization in Asia, Africa and Latin America. 18 (2), 23–28.
Ferdowsian, R., Ryder, A., Kelly, J. (1997) “Evaluation of deep, open drains in North Stirling Area”. Department of Agriculture and Food, Government of Western Australia. R161.
Foster, G.R. (1986) “Understanding ephemeral gully erosion”. In: National Research council, Board on Agriculture. Soil Conservation: An Assessment of the National Resources Inventory, Volume 2. Washington, DC: The National Academies Press, pp. 90-125.
Fox, W.E. (1964) “A study of bulk density and water in a swelling soil”. Soil Science. 98 (5), 307-316.
Friedel, J.K., Munch, J.C., Fischer, W.R. (1996) "Soil microbial properties and the assessment of available soil organic matter in a haplic Luvisol after several years of different cultivation and crop rotation". Soil Biology & Biochemistry. 28 (4-5), 479-488.
Fryirs, K.A., Brierley, G.J. (2012) Geomorphic Analysis of River Systems: An Approach to Reading the Landscape. Wiley-Blackwell.
Gardner, W.H. (1986) “Water Content”. In: Klute, A. (Ed.) Methods of Soil Analysis. Part 1. Physical and Mineralogical Methods. pp. 493-544.
Gebreegziabher, T., Nyssen, J., Govaerts, B., Getnet, F., Behailu, M., Haile, M., Deckers, J. (2009) “Contour furrows for in situ soil and water conservation, Tigray, Northern Ethiopia”. Soil & Tillage Research. 103 (2), 257-264.
Gebremichael, D., Nyssen, J., Poesen, J., Deckers, J., Haile, M., Govers, G., Moeyersons, J. (2005) “Effectiveness of stone bunds in controlling soil erosion on cropland in the Tigray Highlands, northern Ethiopia”. Soil Use and Management. 21 (3), 287-297.
Gessess, G.D. (2014) “Assessment of soil erosion in the Blue Nile basin”. In: Melesse, A., Abtew, W., Setegn, S.G. Nile River Basin: Ecohydrological Challenges, Climate Change and Hydropolitics. Springer. pp. 193-219.
Girmay, G., Singh, B.R., Nyssen, J., Borrosen, T. (2009) “Runoff and sediment-associated nutrient losses under different land uses in Tigray, Northern Ethiopia”. Journal of Hydrology. 376 (1-2), 70-80.
Govers, G., Everaert, W., Poeseu, J., Rauws, G., De Ploey, J., Latridou, J.P. (1990) “A long flume study of the dynamic factors affecting the resistance of a loamy soil to concentrated flow erosion”. Earth Surface Processes and Landforms. 15 (4), 313–328.
Graf, W.L. (2010) “Network characteristics in suburbanizing streams”. Water Resources Research. 13 (2), 459-463.
Gregory, K.J., Walling, D.E. (1968) “The variation of drainage density within a catchment”. International Association of Scientific Hydrology. 13(2), 61-68.
Gregory, K.J., Walling, D.E. (1973) Drainage Basin Form and Process: A Geomorphological Approach. Wiley.
Haile, G.W., Fetene, M. (2012). “Assessment of soil erosion hazard in Kilie catchment, East Shoa, Ethiopia”. Land Degradation & Development. 23 (3), 293-306.
Harden, C.P. (1992) “Incorporating roads and footpaths in watershed-scale hydrologic and soil-erosion models”. Physical Geography. 13 (4), 368-385.
Haregeweyn, N., Poesen, J., Nyssen, J., Verstraeten, G., de Vente, J., Govers, G., Deckers, S., Moeyersons, J. (2005) “Specific sediment yield in Tigray-Northem Ethiopia: Assessment and semi-quantitative modelling”. Geomorphology. 69 (1-4), 315-331.
Haregeweyn, N., Berhe, A., Tsunekawa, A., Tsubo, M., Meshesha, D.T. (2012a) “Integrated watershed management as an effective approach to curb land degradation: A case study of the enabered watershed in Northern Ethiopia”. Environmental Management. 50 (6), 1219-1233.
Haregeweyn, N., Fikadu, G., Tsunekawa, A., Tsubo, M., Meshesha, D.T. (2012b) “The dynamics of urban expansion and its impacts on land use/land cover change and small-scale farmers living near the urban fringe: A case study of Bahir Dar, Ethiopia”. Landscape and Urban Planning. 106 (2), 149-157.
Hawkins, R.H., Ward, T.J., Woodward, D.E., Van Mullem, J.A. (2009) “Curve Number Hydrology. State of the Practice”. American Society of Civil Engineers, Virginia.
Hebrard, O., Voltz, M., Andrieux, P., Moussa, R. (2006) “Spatio-temporal distribution of soil surface moisture in a heterogeneously farmed Mediterranean catchment”. Journal of Hydrology. 329 (1-2), 110-121.
Herweg, K., Ludi, E. (1999) “The performance of selected soil and water conservation measures-case studies from Ethiopia and Eritrea”. Catena. 36 (1-2), 99-114.
Hicks, D.M., Mason, P.D. (1998) Roughness Characteristics of New Zealand Rivers. Water Resources Publications.
Hillel, D. (2004) Introduction to Environmental Soil Physics. Amsterdam: Elsevier.
Hirpa, F.A., Gebremichael, M., Hopson, T. (2010) “Evaluation of High-Resolution Satellite Precipitation Products over Very Complex Terrain in Ethiopia”. Journal of Applied Meteorology and Climatology. 49 (5), 1044-1051.
Hoaglin, D.C., Iglewicz, B., Tukey, J.W. (1986) “Performance of Some Resistant Rules for Outlier Labeling”. American Statistical Association. 81 (396), 991-999.
Holden, S.T., Shiferaw, B. (2000) Development Paths and Policies for Sustainable Land Mangement in Andit Tid, North Shewa. An Exploration of Policy Alternatives. Paper presented at the National Workshop on Policies for Sustainable Land Management in Addis Ababa, May 22–23.
Holden, J., Chapman, P.J., Labadz, J.C. (2004) “Artificial drainage of peatlands: hydrological and hydromchemical process and wetland restoration”. Progress in Physical Geography. 28 (1), 95-123.
Hood, M.J., Clausen, J.C., Warner, G.S. (2007) “Comparison of Stormwater Lag Times for Low Impact and Traditional Residential Development”. Journal of the American Water Resources Association. 43 (4), 1036-1046.
Hooke, J.M. (1979) “An analysis of the processes of river bank erosion”. Journal of Hydrology. 42 (1-2), 39-62.
Hopp, L., McDonnell, J.J. (2009) “Connectivity at the hillslope scale: Identifying interactions between storm size, bedrock permeability, slope angle and soil depth”. Journal of Hydrology. 375 (3-4), 378-391.
Horton, R. E. (1932) “Drainage basin characteristics”. American Geophysical Union. 13 (1), 350-361.
Horton, R. E. (1933) “The role of infiltration in the hydrologic cycle”. Transactions American Geophysical Union. 14 (1), 446-460.
Horton, R. E. (1945) “Erosional development of streams and their drainage basins”. Geologogical Society of America Bulletin. 56 (3), 275-370.
Hudec, P.P., Simpson, F., Akpokodje, E.G., Umenweke, M.O. (2005) “Anthropogenic contribution to gully initiation and propagation in southeastern Nigeria”. Reviews in Engineering Geology. 16, 149-158.
Hurni, H. (1989) Soil for the Future. Environmental Research for Development Cooperation. Berne: Uni Press 62, University of Berne.
Hurni, H. (1990) “Degradation and conservation of soil resources in the Ethiopian Highlands”. Mountain Research and Development. 8 (2-3), 123–130.
Hurni, H., Tato, K., Zeleke, G. (2005) “The implications of changes in population, land use, and land management for surface runoff in the upper Nile Basin area of Ethiopia”. Mountain Research and Development. 25 (2), 147-154.
Ireland, H.A., Sharpe, C.F.S., Eargle, D.H. (1939) Principles of Gully Erosion in the Piedmont of South Carolina. Washingon: U.S. Department of Agriculture.
James, A.L., Roulet, N.T. (2009) “Antecedent moisture conditions and catchment morphology as controls on spatial patterns of runoff generation in small forest catchments”. Journal of Hydrology. 377 (3-4), 351-366.
Jarrett, R. (1984) “Hydraulics of high‐gradient streams”. Journal of Hydraulic Engineering. 110 (11), 1519–1539.
Jarret, R.D. (1987) “Errors in slope-area computations of peak discharges in mountain streams”. Journal of Hydrology. 96 (1-4), 53-67.
Kamara, C.S., Haque, I. (1987) "Soil moisture related properties of vertisols in the Ethiopian highlands". In: Jutzi, S.C., Haque, I., McIntire, J., Stares, J.E.S. (Eds.) Management of Vertisols in Sub-Saharan Africa. Proceedings of a conference held at ILCA, Addis Ababa, Ethiopia, 31 August-4 September 1987. ILCA, Addis Ababa. pp. 183-200.
Kassa, T., Van Rompaey, A., Poesen, J. (2010) “Land suitability assessment for different irrigation methods in korir watershed, northern Ethiopia”. Journal of the Drylands. 3 (2), 214-219.
Kebbede, G., Jacob, M.J. (1988) “Drought, famine and the political-economy of environmental degradation in Ethiopia”. Geography. 73 (318), 65-70.
Kebede, S., Travi, Y., Alemayehu, T., Marc, V. (2006) “Water balance of Lake Tana and its sensitivity to fluctuations in rainfall, Blue Nile basin, Ethiopia”. Journal of Hydrology. 316 (1-4), 233-247.
Kebede, S., Admasu, G., Travi, Y. (2011) “Estimating ungauged catchment flows from Lake Tana floodplains, Ethiopia: an isotope hydrological approach”. Isotopes in Environmental and Health Studies. 47 (1), 71-86.
Kim, J., Kim, W., Lee, C., Kim, Y.J. (2009) "Characteristics of roughness coefficient associated with discharge in gravel-bed river". In: Zhang, C., Tang, H. Advances in Water Resources and Hydraulic Engineering. Beijing: Tsingua University Press. pp. 963-968.
Knapen, A., Poesen, J. (2010) “Soil erosion resistance effects on rill and gully initiation points and dimensions”. Earth Surface Processes and Landforms. 35 (2), 217-228.
Koivusalo, H., Ahti, E., Lauren, A., Kokkonen, T., Karvonen, T., Nevalainen, R., Finer, L. (2008) “Impacts of ditch cleaning on hydrological processes in a drained peatland forest”. Hydrology and Earth System Sciences. 12 (5), 1211-1227.
Koul, D.N., Panwar, P. (2012) "Soil carbon buildup and bioeconomics of different landuses in humid subtropics of West Bengal, India". Annals of Forest Research. 55 (2), 253-264.
Krüger, H.J., Berhanu, F., Yohannes, G.M., Kefane, K. (1996) “Creating an inventory of indigenous soil and water conservation measures in Ethiopia”. In: Reij, C., Scoones, I., Toulmin, C. (Eds.) Sustaining the Soil: Indigenous Soil and Water Conservation in Africa. London: EarthScan Publications, pp. 170–180.
Kumar, R., Chatterjee, C. (2005) “Regional flood frequency analysis using L-moments for North Brahmaputra region of India”. Journal of Hydrologic Engineering. 10 (1), 1-7.
Kuron, H. und Jung, L. (1957) “Uber die Erodiebarkeit einiger Boden”. International Association of Scientific Hydrology-Bulletin 1. pp. 161-165.
Kuru, A. (1978) “The Environmental Impact of Agriculture in Ethiopia”. Environmental Conservation. 5 (3), 213-221.
Lanckriet, S., Derudder, B., Naudts, J., Bauer, H., Deckers, J., Haile, M. and Nyssen, J. (2014) “A political ecology perspective of land degradation in the northern Ethiopian highlands”. Land Degradation and Development. Online early view. DOI: 10.1002/ldr.2278.
Le Bissonnais, Y., Singer, M.J., Bradford, J.M. (1993) “Assessment of soil erodibility: the relationship between soil properties, erosion processes and susceptibility to erosion”. In: Wicherek, S. (Ed.) Farm Land Erosion: in Temperate Plains Environment and Hills. Elsevier Science Publishers, pp. 87– 96.
Lemenih, M., Karltun, E., Olsson, M. (2005) "Assessing soil chemical and physical property responses to deforestation and subsequent cultivation in smallholders farming system in Ethiopia". Agricultue Ecosystems & Environment. 105 (1-2), 373-386.
Lepsch, I.F., Menk, J.R.F., Oliveria, J.B. (1994) “Carbon storage and other properties of soils under agriculture and natural vegetation in Sao Paulo State, Brazil”. Soil Use and Management. 10 (1), 34–42.
Le Roux, J.J., Sumner, P.D. (2012) “Factors controlling gully development: Comparing continuous and discontinuous gullies”. Land Degradation and Development. 23 (5), 440-449.
Ligdi, E.E., Morgan, R.P.C. (1995) “Contour grass strips - a laboratory simulation of their role in soil-erosion control”. Soil Technology. 8 (2), 109-117.
Liu, B. M., Collick, A. S., Zeleke, G., Adgo, E., Easton, Z. M., Steenhuis, T. S. (2008) “Rainfall-discharge relationships for a monsoonal climate in the Ethiopian highlands”. Hydrological Processes. 22 (7), 1059–1067.
Luthin, J.N. (1966) Drainage Engineering. New York: Wiley.
Manning, R. (1891) “On the flow of water in open channels and pipes”. Transactions of the Institution of Civil Engineers of Ireland. 20, 161-207.
Marcus, W.A., Roberts, K., Harvey, L., Tackman, G. (1992) "An evaluation of methods for estimating Mannings-n in small mountain streams". Mountain Research and Development. 12 (3), 227-239.
Martinez-Casasnovas, J.A., Ramos, M.C., Ribes-Dasi, M. (2005) “On-site effects of concentrated flow erosion in vineyard fields: some economic implications”. Catena. 60 (2), 129-146.
Martinez-Mena, M., Albaladejo, J., Castillo, V.M. (1998) “Factors influencing surface runoff generation in a Mediterranean semi-arid environment: Chicamo watershed, SE Spain”. Hydrological Processes. 12 (5), 741-754.
McHugh, O.V., Steenhuis, T.S., Abebe, B., Fernandes, E.C.M. (2007) “Performance of in situ rainwater conservation tillage on dry spell mitigation and erosion control in the drought-prone North Wello zone of the Ethiopian highlands”. Soil & Tillage Research. 97 (1), 19-36.
McIntyre, D.S. (1984) “The physics of volume change in cracking clay soils and the one dimensional misconception”. In: McGarity, J.W., Hoult, E.H., So, H.B. (Eds). The properties and Utilization of Cracking Clay Coils. Reviews in Rural Science No. 5. University of New England, Armidale, NSW, Australia. pp. 116-122.
Mekuria, A., Vlek, P.L.G., Denich, M. (2012) “Application of the caesium-137 technique to soil degradation studies in the Southwestern Highlands of Ethiopia”. Land Degradation & Development. 23 (5), 456-464.
Meshesha, D.T., Tsunekawa, A., Tsubo, M. (2012) “Continuing land degradation: Cause-effect in Ethiopia's Central Rift Valley”. Land Degradation & Development. 23 (2), 130-143.
Meyers, W.R.C. (1978) “Velocity and discharge in compound channels”. Journal of Hydraulic Engineering. 113 (6), 753-766.
Million, A. (1996) “Traditional ditches in northern Shewa, Ethiopian highlands”. In: Reij, C., Scoones, I., Toulmin, C.C. (Eds.) Sustaining the Soil: Indigenous Soil and Water Conservation in Africa. London, UK: IIED. pp. 163–169.
Miserez, A. (2013) Soil Erodibility and Mapping in Different Hydrological Land Systems of Lake Tana Basin, Ethioopia. Unpublished thesis. KULeuven.
Moeyersons, J., Nyssen, J., Poesen, J., Deckers, J., Haile, M. (2006) “On the origin of rock fragment mulches on Vertisols: A case study from the Ethiopian highlands”. Geomorphology. 76 (3-4), 411-429.
Monsieurs, E., Dessie, M., Poesen, J., Deckers, J., Verhoest, N., Nyssen, J., Adgo, E. (2014) “Seasonal surface drainage of sloping farmland and its hydrogeomorphic impacts”. Land Degradation & Development. Online early view. DOI: 10.1002/ldr.2286.
Montgomery, D.R.D., Dietrich, L.W.E. (1994) “Landscape dissection and drainage area-slope thresholds”. In: Kirby, M.J. (Ed.) Process Models and Theoretical Geomorphology. Chichester: John Wiley & Sons. pp. 221-246.
Morgan, R.P.C., Mngomezulu, D. (2003) “Threshold conditions for initiation of valley-side gullies in the Middle Veld of Swaziland”. Catena. 50 (2-4), 401-414.
Morrison, J.E., Gerik, T.J., Chichester, F.W., Martin, J.R., Chandler, J.M. (1990) “A no-tillage farming system for clay soils”. Journal of Production Agriculture. 3 (2), 219–227.
Moussa, R., Voltz, M., Andrieux, P. (2002) “Effects of the spatial organization of agricultural management on the hydrological behaviour of a farmed catchment during flood events”. Hydrological Processes. 16 (2), 393-412.
Mwendera, E., Mohamed, S.M. (1997) “Infiltration rates, surface runoff, and soil loss as influenced by grazing pressure in the Ethiopian highlands”. Soil Use and Management. 13 (1), 29– 35.
Nachtergaele, J., Poesen, J., Sidorchuk, A., Torri, D. (2002) “Prediction of concentrated flow width in ephemeral gully channels”. Hydrological Processes.16 (10), 1935-1953.
Ngatcha, B.N.,Ekodeck, G.E., Mpele, M., Ntana, P.E. (2011) “Hydrological and geotechnical investigations of mass movements in an equatorial city (Yaounde, Cameroon)”. Environmental Earth Sciences. 62 (8), 1733-1747.
Nyalemegbe, K.K., Darkwa, E.O., Yangyuoru, M., Mawunya, F.D., Acquah, D.K., Oteng, J.W., Terry, P.J., Willcocks, T.J.(2010) “The effect of camber bed drainage landforms on soil nutrient distribution and grain yield of maize on the vertisols of the Accra Plains of Ghana”. West African Journal of Applied Ecology. 16 (1), 1-8.
Nyssen, J., Poesen, J., Haile, M., Moeyersons, J., Deckers, J. (2000) "Tillage erosion on slopes with soil conservation structures in the Ethiopian highlands". Soil & Tillage Research. 57 (3), 115-127.
Nyssen, J., Haile, M., Poesen, J., Deckers, J., Moeyersons, J. (2001) “Removal of rock fragments and its effect on soil loss and crop yield, Tigray, Ethiopia”. Soil Use and Management. 17 (3), 179–187.
Nyssen, J., Poesen, J., Moeyersons, J., Lavrysen, Haile, M., Deckers, J. (2002a) “Spatial distribution of rock fragments in cultivated soils in northern Ethiopia as affected by lateral and vertical displacement processes”. Geomorphology. 43 (1-2), 1-16.
Nyssen, J., Poesen, J., Moeyersons, J., Luyten, E., Veyret-Picot, M., Deckers, J., Haile, M., Govers, G. (2002b) “Impact of road building on gully erosion risk: A case study from the northern Ethiopian Highlands”. Earth Surface Processes and Landforms. 27 (12), 1267-1283.
Nyssen, J., Poesen, J., Moeyersons, J., Deckers, J., Haile, M., Lang, A. (2004) “Human impact on the environment in the Ethiopian and Eritrean highlands - a state of the art”. Earth-Science Reviews. 64 (3-4), 273-320.
Nyssen J, Vandenreyken H, Poesen J, Moeyersons J, Deckers J, Mitiku Haile, Salles C, Govers G. (2005) “Rainfall erosivity and variability in the Northern Ethiopian Highlands”. Journal of Hydrology. 311 (1-4), 172 –187.
Nyssen, J., Poesen, J., Gebremichael, D., Vancampenhout, K., D'Aes, M., Yihdego, G., Govers, G., Leirs, H., Moeyersons, J., Naudts, J., Haregeweyn, N., Haile, M., Deckers, J. (2007) “Interdisciplinary on-site evaluation of stone bunds to control soil erosion on cropland in Northern Ethiopia”. Soil & Tillage Research. 94 (1), 151-163.
Nyssen, J., Poesen, J., Moeyersons, J., Haile, M., DEckers, J. (2008) “Dynamics of soil erosion rates and controlling factors in the Northern Ethiopian Highlands – towards a sediment budget”. Earth Surface Processes and Landforms. 33 (5), 695-711.
Nyssen, J., Clymans, W., Descheemaeker, K., Poesen, J., Vandecasteele, I., Vanmaercke, M., Zenebe, A., Van Camp, M., Haile, M., Haregeweyn, N., Moeyersons, J., Martens, K., Gebreyohannes, T., Deckers, J., Walraevens, K. (2010) “Impact of soil and water conservation measures on catchment hydrological response-a case in north Ethiopia”. Hydrological Processes. 24 (13), 1880-1895.
Nyssen, J., Govaerts, B., Araya, T., Cornelis, W.M., Bauer, H., Haile, M., Sayre, K., Deckers, J. (2011) “The use of the marasha ard plough for conservation agriculture in Northern Ethiopia”. Agronomy for Sustainable Development. 31 (2), 287-297.
Oti, N.N. (2004) "Discriminant functions for classifying erosion degraded lands at otamiri, south eastern Nigeria". Journal of Agriculture, Food, Environment and Extension. 3 (1), 34-40.
Oygarden, L., Kvaerner, J., Jenssen, P.D. (1997) “Soil erosion via preferential flow to drainage systems in clay soils”. Geoderma. 76 (1-2), 65-86.
Pathak, P., Wani, S.P., Sudi, R. (2005) Gully Control in SAT Watersheds. Global theme on agroecosystems Report no 15. Patancheru 502 324, Andhara Pradesh, India: International Crops Research Institute for the Semi-Arid Tropics.
Patton, P.C., Schumm, S.A. (1975) “Gully Erosion, Northwestern Colorado - Threshold Phenomenon”. Geology. 3 (2), 88-90.
Poesen, J., Ingelmosanchez, F., Mucher, H. (1990) “The Hydrological Response of Soil Surfaces to Rainfall as Affected by Cover and Position of Rock Fragments in the Top Layer”. Earth Surface Processes and Landforms. 15 (7), 653-671.
Poesen, J. (1993) “Gully typology and gully control measures in the European loess belt”. In: Wicherek, S. (Ed.) Farm Land Erosion in Temperate Plains Environment and Hills. Amsterdam: Elsevier, pp. 221– 239.
Poesen, J., Torri, D., Bunte, K. (1994) “Effects of rock fragments on soil erosion by water at different spatial scales: a review”. Catena. 23 (1-2), 141–166.
Poesen, J., Hooke, J.M. (1997) “Erosion, flooding and channel management in the Mediterranean environments of southern Europe”. Progress in Physical Geography. 21 (2), 157– 199.
Poesen, J., Vandekerckhove, L., Nachtergaele, J., Oostwoud Wijndenes, D., Verstraeten, G., Van Wesemael, B. (2002) “Gully erosion in Dryland Environments”. In: Bull, L.J., Kirby, M.J. (Eds.) Dryland Rivers: Hydrology and Geomorphology of Semi-arid Channels. Chichester: John Wiley & Sons Ltd. pp. 229-263.
Poesen, J., Nachtergaele, J., Verstraeten, G., Valentin, C. (2003) “Gully erosion and environmental change: importance and research needs”. Catena. (50 (2-4), 91-133.
Poesen, J., Vanwalleghem, T., de Vente, J., Knapen, A., Verstraeten, G., Martínez-Casasnovas, J.A. (2006) “Gully erosion in Europe”. In: Boardman J, Poesen J. (Eds.) Soil Erosion in Europe. Chichester, UK: John Wiley & Sons, Ltd.
Poff, B., Leao, D., Tecle, A., Neary, D.G. (2005) “Determining watershed boundaries and area using GPS, DEMs, and traditional methods: a comparison”. In: van Riper, C., Mattson, D.J. (Eds.) The Colorado Plateau II. Biophysical, Socioeconomic, and Cultural Research. Arizona, USA: University of Arizona Press.
Ponce, V.M., Hawkins, R.H. (1996) “Runoff curve number: has it reached maturity?”. Journal of Hydrologic Engineering. 1 (1), 11-19.
Poppe, L. (2012) Geomorphology of Lake Tana Basin, Ethiopia. Unpublished thesis. UGent: Department of Geography.
Poppe, L., Frankl, A., Poesen, J., Teshager Admasu, Mekete Dessie, Enyew Adgo, Deckers, J., Nyssen, J. (2013) “Geomorphological map of the Lake Tana basin (Ethiopia)”. Journal of Maps. 9 (3), 431-437.
Qureshi, A.S., Ahmad, W., Ahmad, A.A. (2013) “Optimum groundwater table depth and irrigation schedules for controlling soil salinity in central Iraq”. Irrigation and Drainage. 62 (4), 414-424.
Reij, C., Scoones, I., Toulmin, C. (1996) Sustaining the Soil: Indigenous Soil and Water Conservation in Africa. London: Earthscan Publications Ltd.
Rientjes, T.H.M., Haile, A.T., Kebede, E., Mannaerts, C.M.M., Habib, E., Steenhuis, T.S. (2011) “Changes in land cover, rainfall and stream flow in Upper Gilgel Abbay catchment, Blue Nile basin-Ethiopia”. Hydrology and Earth System Sciences. 15 (6), 1979-1989.
Robinson, M. (1990) Impact of Improved Land Drainage on River Flows. Institute of Hydrology, Rep. No. 113. Crowmarsh Gifford, Wallingford, Oxon, U.K.
Rodriguez-Blanco, M.L., Taboada-Castro, M.M., Taboada-Castro, M.T. (2013) “Linking the field to the stream: Soil erosion and sediment yield in a rural catchment, NW Spain”. Catena. 102, 74-81.
Schneiderman, E.M., Pierson, D.C., Lounsbury, D.G., Zion, M.S. (2002) “Modeling the hydrochemistry of the Cannonsville watershed with generalized watershed loading functions (GWLF)”. Journal of the American Water Resources Association. 38 (5), 1323-1347.
Schot, P.P., Dekker, S.C., Poot, A. (2004) “The dynamic form of rainwater lenses in drained fens”. Journal of Hydrology. 293 (1-4), 74-84.
Schürz, C., Schwen, A., Strohmeier, S., Klik, A. (2013) Do Stone Bunds Affect Soil Physical Properties? A Case Study in Northern Ethiopia. Paper presented at the EGU General Assembly 2013, Vienna, Austria. Geophysical Research Abstracts, Vol. 15, EGU2013-4880-1.
Schuyt, K.D. (2005) “Economic consequences of wetland degradation for local populations in Africa”. Ecological Economics. 53 (2), 177-190.
Setegn, S.G., Srinivasan, R., Dargahi, B., Melesse, A.M. (2009) “Spatial delineation of soil erosion vulnerability in the Lake Tana Basin, Ethiopia”. Hydrological Processes. 23 (26), 3738-3750.
Setegn, S.G., Srinivasan, R., Melesse, A.M., Dargahi, B. (2010) “SWAT model application and prediction uncertainty analysis in the Lake Tana Basin, Ethiopia”. Hydrologycal Processes. 24 (3). 357-367.
Shahin, M. (1988) Hydrology of the Nile basin, International Institute for Hydraulic and Environmental Engineering. The Netherlands: Elsevier.
Shiferaw, M. (2002) Linking Indigenous with ‘Conventional’ Measures for Substainable Land Management in the Highlands of Ethiopia: A Case Study of Digil Watershed, East Gojjam. Unpublished thesis. Addis Ababa University: College of Social Sciences.
Shiferaw, T. (2012) Effects of Inorganic Fertilizer Types and Sowing Methods of Variable Seed Rates on Yield and Yield Components of Tef [Eragostis Tef (Zucc.)Trotte] In Ada'A Woreda, Central Ethiopia. Unpublished thesis. Haramaya University, Ethiopia.
Sidle, R.C., Ziegler, A.D., Negishi, J.N., Nik, A.R., Siew, R., Turkelboom, F. (2006) “Erosion processes in steep terrain - truths, myths, and uncertainties related to forest management in Southeast Asia”. Forest Ecology and Management. 224 (1-2), 199–225.
Simane, B., Zaitchik, B.F., Ozdogan, M. (2013) “Agroecosystem Analysis of the Choke Mountain Watersheds, Ethiopia”. Sustainability. 5 (2), 592-616.
Simon, A., Rinaldi, M. (2006) “Disturbance, stream incision, and channel evolution: The roles of excess transport capacity and boundary materials in controlling channel response”. Geomorphology. 79 (3-4), 361-383.
Singh, G.R., Prakash, O.M. (1985) "Characteristics and Erodibility of Some Hill Soils in Uttar Pradesh under Varying Land Use, Slope and Terracing Conditions". Journal of the Indian Society of Soil Science. 33 (4), 858-864.
Singh, S., Agnihotri, S.P. (1987) “Rill and gully erosion in the sub humid tropical riverine environment of Teonthar Tahsil, Madhya Pradesh, India”. Geografiska Annaler Series A-Physical Geography. 69 (1), 227-236.
Sivapragasam, C., Muttil, N. (2005) “Discharge rating curve extension - A new approach”. Water Resources Management. 19 (5), 505-520.
Skaggs, R. W., Brevé, M. A., Gilliam, J. W. (1994) “Hydrologic and water quality impacts of agricultural Drainage”. Critical Reviews in Environmental Science and Technology. 24 (1), 1-32.
Smit, H., Tefera, G. (2011) Understanding Land Degradation on a Hill Slope of the Choke Mountains in Ethiopia. Conference paper -Building resilience to Climate Change in the Blue Nile highlands, Addis Ababa, Ethiopia.
Spaling, H., Smit, B. (1995) “A conceptual-model of cumulative environmental-effects of agricultural land drainage”. Agricultural Ecosystems & Environment. 35 (2), 99-108.
Srivastava, K.L., Abiye, A., Tekalign, M., Hailu, R., Selamyihun, K. (1993) “Land, soil and water management”. In: Tekalign M, Abiye A, Srivastava KL, Asgelil D (Eds). Improved Management of Vertisols for Sustainable Crop-livestock Production in the Ethiopian Highlands: Synthesis Report 1986-92. Technical committee of the joint vertisol project, Addis Ababa, Ethiopia. pp. 75-84
Steegen, A., Govers, G., Takken, I., Nachtergaele, J., Poesen, J., Merckx, R. (2001) “Factors controlling sediment and phosphorous export from two Belgian agricultural catchments”. Journal of Environmental Quality. 30 (4),1249–1258.
Steenhuis, T.S., Collick, A.S., Easton, Z.M., Leggesse, E.S., Bayabil, H.K., White, E.D., Awulachew, S.B., Adgo, E., Ahmed, A.A. (2009) “Predicting discharge and sediment for the Abay (Blue Nile) with a simple model”. Hydrological Processes. 23 (26), 3728-3737.
Sukiyah, E., Hirnawan, T.F., Muslim, D. (2010) "The Erosion Model Based on Grainsize Distribution Ratios of Weathering Product of Quaternary Volcanic Deposits". Facing the Challenges-Building the Capacity. FIG Congress, Sydney, Australia.
Sutcliffe, J.V., Parks, Y.P. (1999) The Hydrology of the Nile. IAHS Special Publication no. 5. Oxfordshire, UK: International Association of Hydrological Sciences.
Swiechowicz, J. (2011) “The development of ephemeral gullies in cultivated areas of Wisnicz Foothills, Poland”. Landform Analysis. 17, 209-214.
Takken, I., Govers, G., Steegen, A., Nachtergaele, J., Guérif, J. (2001) “The prediction of runoff flow directions on tilled fields”. Journal of Hydrology. 248 (1-4), 1–13.
Tana-Beles WME Reports (2011). Baseline for Watershed Development. N°37 Main Report for Natural Resources Survey, Bahir Dar.
Tardif, S., St-Hilaire, A., Roy, R., Bernier M., Payette, S. (2009) “Statistical properties of hydrographs in minerotrophic fens and small lakes in mid-latitude Québec, Canada”. Canadian Water Resouces Journal. 34 (4), 365-380.
Taye, G., Poesen, J., Van Wesemael, B., Vanmaercke, M., Teka, D., Deckers, J., Goosse, T., Maetens, W., Nyssen, J., Hallet, V., Haregeweyn, N. (2013) “Effects of land use, slope gradient, and soil and water conservation structures on runoff and soil loss in semi-arid Northern Ethiopia”. Physical Geography. 34 (3), 236-259.
Tebebu, T. Y., Abiy, A. Z., Dahlke, H. E., Easton, Z. M., Zegeye, A. D., Tilahun, S. A., Collick, A. S., Kidnau, S., Moges, S., Dadgari, F., Steenhuis, T. S. (2010) “Surface and subsurface flow effect on permanent gully formation and upland erosion near Lake Tana in the Northern Highlands of Ethiopia”. Hydrology and Earth System Sciences. 14 (11), 2207-2217.
Temesgen, M., Rockström J., Savenije H.H.G., Hoogmoed W.B., Alemu, D. (2008) “Determinants of tillage frequency among smallholder farmers in two semi-arid areas in Ethiopia”. Physics and Chemistry of the Earth. 33 (1-2), 183–191.
Tesfaye, K., Walker, S. (2004) “Matching of crop and environment for optimal water use: the case of Ethiopia”. Physics and Chemistry of the Earth. 29 (15-18), 1061-1067.
Thomasson, A.J. (1975) “Hydrological and environmental aspects”. In: Thomasson, A.J. (Ed.) Soils and Field Drainage. Technical Monograph No. 7. Soil Survey of England and Wales, Harpenden; 62-65.
Tilahun, S.A., Guzman, C.D., Zegeye, A.D., Engda, T.A., Collick, A.S., Rimmer, A., Steenhuis, T.S. (2013) “An efficient semi-distributed hillslopeerosion model for the subhumid Ethiopian Highlands”. Hydrology and Earth System Sciences. 17 (3), 1051-1063.
Torri, D., Poesen, J. (2014) “A reviewof topographic threshold conditions for gully head development in different environments”. Earth-Science Reviews. 130, 73–85.
Toy, T.J., Foster, G.R., Renard, K.G. (2002) Soil Erosion: Processes, Prediction, Measurement, and Control. New York: John Wiley and Sons Ltd.
Trafford, B.D. (1973) The Relationship Between Field Drainage and Arterial Drainage - Theoretical Aspects. FDEU Technical Bulletin. 73/10.
Tukey, J.W. (1977) Exploratory Data Analysis. Eading, MA: Addison-Wesley.
Turkelboom, F., Poesen, J., Trebuil, G. (2008) “The multiple land degradation effects caused by land-use intensification in tropical steeplands: A catchment study from northern Thailand”. Catena.75 (1), 102-116.
Valentin, C., Poesen, J., Li, Y. (2005) “Gull erosion: impacts, factors and control”. Catena. 63 (2-3), 132-153.
Vandaele, K., Poesen, J., Govers, G., vanWesemael, B. (1996) “Geomorphic threshold conditions for ephemeral gully incision”. Geomorphology. 16 (2), 161-173.
Vandekerckhove, L., Poesen, J., Wijdenes, D.O., de Figueiredo, T. (1998) “Topographical thresholds for ephemeral gully initiation in intensively cultivated areas of the Mediterranean”. Catena. 33 (3-4), 271-292.
van Ledden, M., van Kesteren, W.G.M., Winterwerp, J.C. (2004) "A conceptual framework for the erosion behaviour of sand-mud mixtures". Continental Shelf Research.24 (1), 1-11.
Vanmaercke, M., Zenebe, A., Poesen, J., Nyssen, J., Verstraeten, G., Deckers, J. (2010) “Sediment dynamics and the role of flash floods in sediment export from medium-sized catchments: a case study from the semi-arid tropical highlands in northern Ethiopia”. Journal of Soil and Sediments. 10 (4), 611-627.
Vanwalleghem, T., Van Den Eeckhaut, M., Poesen, J., Deckers, J., Nachtergaele, J., Van Oost, K., Slenters, C. (2003) “Characteristics and controlling factors of old gullies under forest in a temperate humid climate: a case study from the Meerdaal Forest (Central Belgium)”. Geomorphology. 56 (1-2), 15-29.
Vanwalleghem, T., Poesen, J., Nachtergaele, J., Verstraeten, G. (2005) “Characteristics, controlling factors and importance of deep gullies under cropland on loess-derived soils”. Geomorphology. 69 (1-4), 76-91.
van Wambeke, A.R. (1962) “Criteria for classifying tropical soils by age”. Journal of Soil Science. 13 (1), 124-132.
Veldhuisen, C., Russel, P. (1999) “Forest road drainage and erosion initiation in four west-cascade watersheds”. TFW Effectiveness Monitoring Report. Timber/Fish/Wildlife monitoring advisory group and the northwest Indian fisheries commission. (http://www.dnr.wa.gov/Publications/fp_tfw_mag1_99_001.pdf)
Wanjogu, S.N., Muya, E.M., Macharia, P.N., Kamoni, P.T. (2006) Sustainable Land Management in Kiambindu, Kiarukungu, Kyeekolo and Kisioki Samllholder Irrigation Schemes. Kenya Soil Survey Advisory Site Evaluation Report. Kenya Agricultural Research Institute.
Watson, A.M., Ormerod, S.J. (2004) “The microdistribution of three uncommon freshwater gastropods in the drainage ditches of British grazing marshes”. Aquatic Conservation: Marine and Freshwater Ecosystems. 14 (3), 221-236.
Wei, W., Chen, L.D., Fu, B.J., Huang, Z.L., Wu, D.P., Gui, L.D. (2007) “The effect of land uses and rainfall regimes on runoff and soil erosion in the semi-arid loess hilly area, China”. Journal of Hydrology. 335 (3-4), 247-258.
Westphal, E. (1975) Agricultural Systems in Ethiopia. Wageningen: Centre for Agricultural Publishing and Documentation.
Wilkinson, M.E., Quinn, P.F., Benson, I. and Welton, P. (2010) Runoff Management: Mitigation Measures for Disconnecting Flow Pathways in the Belford Burn Catchment to Reduce Flood Risk. Proceedings of the British Hydrological Society International Symposium 2010, Newcastle upon Tyne.
Wischmeier, W.H., Mannering, J.V. (1969) “Relation of soil properties to its erodibility”. Soil Science Society of America. 33,131-137.
Wischmeier, W.H., Smith, D.D. (1978) Predicting Rainfall Erosion Losses: A Guide to conservation Planning. Agriculture Handbook, vol. 537. Washington: United States Department of Agriculture.
Woodward, D.E. (1999) “Method to predict cropland ephemeral gully erosion”. Catena. 37 (3-4), 393– 399.
Yitbarak, T.W., Belliethathan, S., Stringer, L.C. (2012) “The onsite cost of gully erosion and cost-benefit of gully rehabilitation: A case study in Ethiopia”. Land Degradation & Development. 23 (2), 157-166.
Zegeye., A.D., Steenhuis, T.S., Blake, R.W., Kidnau, S., Collick, A.S., Dadgari, F. (2010). “Assessment of soil erosion processes and farmer perception of land conservation in Debre Mewi watershed near Lake Tana, Ethiopia”. Ecohydrology & Hydrobiology. 10 (2-4), 197-306.
Zeleke, G. (2000) Landscape Dynamics and Soil Erosion Process Modeling in the North-western Ethiopian Highlands. Berne, Switzerland: Geographica Bernensia. African Studies Series A 16.
Ziadat, F.M., Taimeh, A.Y. (2013) “Effects of rainfall intensity, slope, land use and antecedent moisture on soil erosion in arid environment”. Land Degradation & Development. 24 (6), 582–590.
Ziegler, A., Sutherland, R.A., Giambelluca, T,W. (2000) “Runoff generation and sediment production on unpaved roads, footpaths and agricultural land surfaces in northern Thailand”. Earth Surface Processes and Landforms. 25 (5), 519-534.
Zhang, Y.G., Wu, Y.Q., Lin, B.Y., Zheng, Q.H., Yin, J.Y. (2007) “Characteristics and factors controlling the development of ephemeral gullies in cultivated catchments of black soil region, Northeast China”. Soil & Tillage Research. 96 (1-2), 28-41.
Zhang, Z.Y., Kong, L.L., Zhu, L., Mwiya, R.M. (2013) “Effect of drainage ditch layout on nitrogen loss by runoff from an agricultural watershed”. Pedosphere. 23 (2), 256–264.
Websites
CountrySTAT. http://213.55.92.108/countrystat/home.aspx?c=ETH. 24/03/2013.
Repeated Measures ANOVA. https://statistics.laerd.com/statistical-guides/repeated-measures-anova…. 08/04/2014.
