Sulluh

It is a confined river, locally meandering in its narrow alluvial plain, with a slope gradient of {{convert|11|m/km}}. With its tributaries, the river has cut a deep gorge.{{cite book |last1=Amanuel Zenebe |first1=and colleagues |title= The Giba, Tanqwa and Tsaliet rivers in the headwaters of the Tekezze basin. In: Geo-trekking in Ethiopia's Tropical Mountains - The Dogu'a Tembien District |date=2019 |publisher=SpringerNature |isbn=978-3-030-04954-6 |doi=10.1007/978-3-030-04955-3_14 |s2cid=199099067 }}

The runoff footprint or annual total runoff volume is {{convert|133000000|m3}}.

Peak discharges up to {{convert|338|m3/sec}} occur in the second part of the rainy season (month of August) when there are strong rains and the soils are saturated with water in many places.

The percentage of total rainfall that directly leaves the catchment as storm runoff (also called runoff coefficient) is 13%.

The total amount of sediment that is transported by this river amounts to {{convert|614000|t}} per year. Median sediment concentration in the river water is {{convert|2.93|g/l}} but may go up to {{convert|43|g/l}}. The highest sediment concentrations occur at the beginning of the rainy season, when loose soil and dust is washed away by overland flow and ends up in the river.{{cite journal |last1=Vanmaercke |first1=M. and colleagues |title=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=Journal of Soils and Sediments |date=2010 |volume=10 |issue=4 |pages=611–627 |doi=10.1007/s11368-010-0203-9 |s2cid=53365853 |url=https://biblio.ugent.be/publication/854315 |hdl=1854/LU-854315 |hdl-access=free }}

As such water contains many nutrients (locally it is called "aygi"), farmers estimate that it strengthens their cattle, which they will bring to the river. All in all, average sediment yield is {{convert|890|t/km2}} and per year. All measurements were done at a purposively installed station near the mouth of the river, in the years 2004–2007.

File:TESFA trek (5498477203).jpg

Runoff mostly occurs in the form of high runoff discharge events that occur in a very short period (called flash floods). These are related to the steep topography, often little vegetation cover and intense convective rainfall. The peaks of such flash floods have often a 50 to 100 times larger discharge than the preceding baseflow. These flash floods mostly occur during the evening or night, because the convective rain showers occur in the afternoon.

File:Cuesta landscape on the road from Wukro to Hauzien.jpg

Evidence given by Italian aerial photographs of the catchment, taken in the 1930s show that 37% of the catchment was covered with woody vegetation (against 40% in 2014). This vegetation, and particularly the newly built conservation structures slow down runoff and impacts the runoff coefficient (9% in 1935 against 13% in 2014). As a consequence, discharges in the river were less than today.{{cite thesis | url=https://biblio.ugent.be/publication/8543686 | title=Hydrological response to land cover and management (1935-2014) in a semi-arid mountainous catchment of northern Ethiopia | year=2017 | publisher=Ghent University | type=dissertation | last1=Dinssa | first1=Etefa Guyassa }}

Up to the 1980s, there was strong pressure on the environment, and much vegetation disappeared.{{cite journal | url=https://www.sciencedirect.com/science/article/pii/S0169555X11000821 | doi=10.1016/j.geomorph.2011.02.018 | title=Linking long-term gully and river channel dynamics to environmental change using repeat photography (Northern Ethiopia) | year=2011 | last1=Frankl | first1=Amaury | last2=Nyssen | first2=Jan | last3=De Dapper | first3=Morgan | last4=Haile | first4=Mitiku | last5=Billi | first5=Paolo | last6=Munro | first6=R. Neil | last7=Deckers | first7=Jozef | last8=Poesen | first8=Jean | journal=Geomorphology | volume=129 | issue=3–4 | pages=238–251 | bibcode=2011Geomo.129..238F }} This river had its greatest discharges and width in that period.

The magnitude of floods in this river has however been decreased in recent years due to interventions in the catchment. On other steep slopes, exclosures have been established; the dense vegetation largely contributes to enhanced infiltration, less flooding and better baseflow.{{cite journal |last1= Descheemaeker|first1= K. and colleagues| title= Runoff on slopes with restoring vegetation: A case study from the Tigray highlands, Ethiopia. |journal= Journal of Hydrology |date=2006 |volume=331 |issue=1–2 |pages=219–241 |doi= 10.1016/j.still.2006.07.011|url= https://biblio.ugent.be/publication/378900|hdl= 1854/LU-378900 |hdl-access= free }} Physical conservation structures such as stone bunds{{cite journal |last1= Nyssen|first1= Jan|last2= Poesen|first2= Jean|last3= Gebremichael|first3= Desta|last4= Vancampenhout|first4= Karen|last5= d'Aes|first5= Margo|last6= Yihdego|first6= Gebremedhin|last7= Govers|first7= Gerard|last8= Leirs|first8= Herwig|last9= Moeyersons|first9= Jan|last10= Naudts|first10= Jozef|last11= Haregeweyn|first11= Nigussie|last12= Haile|first12= Mitiku|last13= Deckers|first13= Jozef|title= Interdisciplinary on-site evaluation of stone bunds to control soil erosion on cropland in Northern Ethiopia. |journal= Soil and Tillage Research |date=2007 |volume=94 |issue=1 |pages=151–163 |doi= 10.1016/j.still.2006.07.011|hdl= 1854/LU-378900|url= https://biblio.ugent.be/publication/378900|hdl-access= free}}{{cite journal |last1= Gebeyehu Taye and colleagues| title= Evolution of the effectiveness of stone bunds and trenches in reducing runoff and soil loss in the semi-arid Ethiopian highlands. |journal= Zeitschrift für Geomorphologie|date=2015 |volume=59 |issue=4 |pages=477–493 |doi= 10.1127/zfg/2015/0166| bibcode= 2015ZGm....59..477T }} and check dams also intercept runoff.{{cite journal |last1= Nyssen|first1= J.|last2= Veyret-Picot|first2= M.|last3= Poesen|first3= J.|last4= Moeyersons|first4= J.|last5= Haile|first5= Mitiku|last6= Deckers|first6= J.|last7= Govers|first7= G.|title= The effectiveness of loose rock check dams for gully control in Tigray, Northern Ethiopia. |journal= Soil Use and Management |date=2004 |volume=20 |pages=55–64 |doi= 10.1111/j.1475-2743.2004.tb00337.x|s2cid= 98547102}}{{cite journal |last1= Etefa Guyassa and colleagues|title= Effects of check dams on runoff characteristics along gully reaches, the case of Northern Ethiopia. |journal= Journal of Hydrology |date=2017 |volume=545 |issue=1 |pages=299–309 |doi= 10.1016/j.jhydrol.2016.12.019|bibcode= 2017JHyd..545..299G |url= https://biblio.ugent.be/publication/8518957 |hdl= 1854/LU-8518957 |hdl-access= free }}

Besides springs and reservoirs, irrigation is strongly dependent on the river’s baseflow. Such irrigated agriculture is important in meeting the demands for food security and poverty reduction. Irrigated lands are established in the narrow alluvial plains along the river in several places.

The valley bottoms in the lower gorge of this river have been identified as a transhumance destination zone.

Transhumance takes place in the summer rainy season, when the lands near the villages are occupied by crops. Young shepherds will take the village cattle down to the gorge and overnight in small caves. The gorges are particularly attractive as a transhumance destination zone, because there is water and good growth of semi-natural vegetation.{{cite journal |title=Transhumance in the Tigray highlands (Ethiopia) |journal=Mountain Research and Development |date=2009 |volume=29 |issue=3 |pages=255–264 |doi=10.1659/mrd.00033 |last1=Nyssen |first1=Jan |last2=Descheemaeker |first2=Katrien |last3=Zenebe |first3=Amanuel |last4=Poesen |first4=Jean |last5=Deckers |first5=Jozef |last6=Haile |first6=Mitiku |doi-access=free |hdl=1854/LU-854326 |hdl-access=free }}

Boulders and pebbles encountered in the river bed can originate from any location higher up in the catchment. In the uppermost stretches of the river, only rock fragments of the upper lithological units will be present in the river bed, whereas more downstream one may find a more comprehensive mix of all lithologies crossed by the river. From upstream to downstream, the following lithological units occur in the catchment.{{cite book |last1=Sembroni |first1=A. |last2=Molin |first2=P. |last3=Dramis |first3=F. |title=Regional geology of the Dogu'a Tembien massif. In: Geo-trekking in Ethiopia's Tropical Mountains — The Dogu'a Tembien District |date=2019 |publisher=SpringerNature |isbn=978-3-030-04954-6 |url=https://www.springer.com/gp/book/9783030049546}}

• Upper basalt
• Interbedded lacustrine deposits
• Lower basalt
• Adigrat Sandstone
• Edaga Arbi Glacials
• Antalo Limestone
• Quaternary freshwater tufa{{cite journal |last1=Moeyersons |first1=J. and colleagues |title=Age and backfill/overfill stratigraphy of two tufa dams, Tigray Highlands, Ethiopia: Evidence for Late Pleistocene and Holocene wet conditions. |journal=Palaeogeography, Palaeoclimatology, Palaeoecology |date=2006 |volume=230 |issue=1–2 |pages=162–178 |bibcode=2006PPP...230..165M |doi=10.1016/j.palaeo.2005.07.013 }}

Trekking routes have been established across and along this river.{{cite book |title=Description of trekking routes in Dogu'a Tembien. In: Geo-trekking in Ethiopia's Tropical Mountains - The Dogu'a Tembien District |series=GeoGuide |date=2019 |publisher=SpringerNature |doi=10.1007/978-3-030-04955-3 |isbn=978-3-030-04954-6 |s2cid=199294303 |url=https://www.springer.com/gp/book/9783030049546}} The tracks are not marked on the ground but can be followed using downloaded .GPX files.{{Cite web|url=https://www.openstreetmap.org/traces/tag/nyssen-jacob-frankl|title=Public GPS Traces tagged with nyssen-jacob-frankl}}

Trek 23 also allows visiting the confluence of Sulluh and Genfel at Shugu'a Shugu'i.

In the rainy season, flash floods may occur and it is advised not to follow the river bed. Frequently, it is then also impossible to wade across the river.{{cite book |chapter=Logistics for the Trekker in a Rural Mountain District of Northern Ethiopia|date=2019 |publisher=Springer-Nature |pages=537–556 |doi=10.1007/978-3-030-04955-3_37 |title=Geo-trekking in Ethiopia's Tropical Mountains |series=GeoGuide |last1=Nyssen |first1=Jan |isbn=978-3-030-04954-6 |s2cid=199198251 }}

• List of Ethiopian rivers

{{reflist}}

Category:Rivers of Ethiopia

Category:Tigray Region

Category:Dogu'a Tembien