Giba River

Giba is a river of northern Ethiopia. It starts at the confluence of Genfel and Sulluh (which rises in the mountains of Mugulat) (3298 metres above sea level) and flows westward to the Tekezé River.[2] Future Lake Giba will occupy the plain where Sulluh, Genfel and Agula'i Rivers meet, and hence be the future source of Giba River.

Giba drainage network

Giba River
The Giba River at Addi Lihtsi
Giba River in Tigray Region
Location
CountryEthiopia
RegionTigray Region
Districts (woreda)Dogu’a Tembien , Inderta, Saharti Samre, Abergele
Physical characteristics
SourceGenfel River
 • locationShugu'a Shugu'i in Emni Ankelalu
 • elevation1,770 m (5,810 ft)
2nd sourceSulluh River
MouthTekezé River
 • location
Down from Jo’amare in Kola Tembien
 • coordinates
13.605°N 38.635°E / 13.605; 38.635
 • elevation
970 m (3,180 ft)
Length121 km (75 mi)
Basin size5,200 km2 (2,000 sq mi)
Width 
 • average40 m (130 ft)
Discharge 
 • locationOld bridge in Debre Nazret[1]
 • maximum1,740 m3/s (61,000 cu ft/s)
Discharge 
 • locationUpstream of the confluence with Tanqwa in Barashuwa[1]
 • maximum551 m3/s (19,500 cu ft/s)
Basin features
River systemPermanent river
Tributaries 
 • leftIlala, May Gabat
 • rightInda Sillasie River, Tanqwa
WaterbodiesFuture Lake Giba, Gereb Segen and many small reservoirs
BridgesQarano, Old bridge (Debre Nazret), Abergele
TopographyMountains and deep gorges

Hydrography

It is a confined river, locally meandering in its narrow alluvial plain, with a slope gradient of 7 metres per kilometre. With its tributaries, the river has cut a deep gorge.[3]

Pool in Giba

Tributaries

Main tributaries, from downstream to upstream, are[2]

Hydrology

Hydrological characteristics

The runoff footprint or annual total runoff volume is 558 million m³. Peak discharges up to 1740 m³ per second 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 8%.[1]

1960s bridge on Giba River at the east of Debre Nazret

The total amount of sediment that is transported by this river amounts to 3.96 million tonnes per year. Median sediment concentration in the river water is 10 grammes per litre, but may go up to 42 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.[4] 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.[3] All in all, average sediment yield is 1065 tonnes per km² and per year. All measurements were done at a purposively installed stations, on Giba and Tanqwa rivers, just upstream of their junction, in the years 2006 and 2007.[4]

Flash floods

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.[3]

Changes over time
Giba River near the outlet of May Gabat, at left a flowering incense tree

Evidence given by Italian aerial photographs of the catchment, taken in the 1930s show that 49% of the catchment was covered with woody vegetation (against 35% in 2014). This vegetation could slow down runoff and the runoff coefficient was smaller (5% in 1935 against 8% in 2014). As a consequence, discharges in the river were less and the river was narrower than today.[5] Up to the 1980s, there was strong pressure on the environment, and much vegetation disappeared.[6] This river had its greatest discharges and width in that period.

Giba river at Inda Mihtsun

The magnitude of floods in this river has however been decreased in recent years due to interventions in the catchment. At Gemgema, Afedena, May Be'ati and on many other steep slopes, exclosures have been established; the dense vegetation largely contributes to enhanced infiltration, less flooding and better baseflow.[7] Physical conservation structures such as stone bunds[8][9] and check dams also intercept runoff.[10][11]

Irrigated agriculture

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.[3] Irrigated lands are established in the narrow alluvial plains all along the river, mostly using pump irrigation. Very often tropical fruits are grown in these gorges as the climate is warmer than the overall surrounding highlands.

Transhumance towards the river gorge

The valley bottoms in the gorge of this river, for instance at Inda Mihtsun, 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.[12]

Boulders and pebbles in the river bed
Giba cascading over Antalo Limestone near the confluence with May Gabat

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.[13]

Logically, in the uppermost stretches of the river, only the pebbles and boulders 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.

Lower Giba bridge

Natural boundary

During its course, this river three different district (“woreda”) borders.[15] On the various parts:

Trekking along the river

Trekking routes have been established across and along this river.[16] The tracks are not marked on the ground but can be followed using downloaded .GPX files.[17]

  • Trek 15, along the middle course of Giba
  • Trek 22, across the Giba gorge in Debre Nazret
  • Trek G, across the Giba gorge in Amanit
  • Treks S1 and S2, across the Giba gorge in Abergele (woreda)

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.[18]

gollark: This is not really right though. Instead of simulating some ridiculously complex alternate universe without the thing, the human could just be anomalously made to not infer anything from the weirdness caused by the antimeme/not perceive its changes.
gollark: Okay, never mind, I can kind of work it out?
gollark: I don't understand what you're saying here.
gollark: It's actually a web application using a horrible gevent-based thing where somehow I have to press ctrl-C 3 times to stop it.
gollark: 🐝, I may have to rewrite the osmarks.tk™ horrible accursed python script controlling everything™ asynchronously.

See also
  • List of Ethiopian rivers

References
  1. Amanuel Zenebe, and colleagues (2013). "Spatial and temporal variability of river flows in the degraded semi-arid tropical mountains of northern Ethiopia". Zeitschrift für Geomorphologie. 57 (2): 143–169. doi:10.1127/0372-8854/2012/0080.
  2. Jacob, M. and colleagues (2019). Geo-trekking map of Dogu'a Tembien (1:50,000). In: Geo-trekking in Ethiopia's Tropical Mountains - The Dogu'a Tembien District. SpringerNature. ISBN 978-3-030-04954-6.
  3. Amanuel Zenebe, and colleagues (2019). 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. SpringerNature. doi:10.1007/978-3-030-04955-3_14. ISBN 978-3-030-04954-6.
  4. Vanmaercke, M. and colleagues (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 Soils and Sediments. 10 (4): 611–627. doi:10.1007/s11368-010-0203-9.
  5. Etefa Guyassa, 2017. PhD thesis. Hydrological response to land cover and management (1935-2014) in a semi-arid mountainous catchment of northern Ethiopia
  6. Frankl, A., Nyssen, J., De Dapper, M., Mitiku Haile, Billi, P., Munro, R.N., Deckers, J. Poesen, J. 2011. Linking long-term gully and river channel dynamics to environmental change using repeat photography (North Ethiopia). Geomorphology, 129 (3-4): 238-251.
  7. Descheemaeker, K. and colleagues (2006). "Runoff on slopes with restoring vegetation: A case study from the Tigray highlands, Ethiopia". Journal of Hydrology. 331 (1–2): 219–241. doi:10.1016/j.still.2006.07.011.
  8. Nyssen, Jan; Poesen, Jean; Gebremichael, Desta; Vancampenhout, Karen; d'Aes, Margo; Yihdego, Gebremedhin; Govers, Gerard; Leirs, Herwig; Moeyersons, Jan; Naudts, Jozef; Haregeweyn, Nigussie; Haile, Mitiku; Deckers, Jozef (2007). "Interdisciplinary on-site evaluation of stone bunds to control soil erosion on cropland in Northern Ethiopia". Soil and Tillage Research. 94 (1): 151–163. doi:10.1016/j.still.2006.07.011. hdl:1854/LU-378900.
  9. Gebeyehu Taye and colleagues (2015). "Evolution of the effectiveness of stone bunds and trenches in reducing runoff and soil loss in the semi-arid Ethiopian highlands". Zeitschrift für Geomorphologie. 59 (4): 477–493. doi:10.1127/zfg/2015/0166.
  10. Nyssen, J.; Veyret-Picot, M.; Poesen, J.; Moeyersons, J.; Haile, Mitiku; Deckers, J.; Govers, G. (2004). "The effectiveness of loose rock check dams for gully control in Tigray, Northern Ethiopia". Soil Use and Management. 20: 55–64. doi:10.1111/j.1475-2743.2004.tb00337.x.
  11. Etefa Guyassa and colleagues (2017). "Effects of check dams on runoff characteristics along gully reaches, the case of Northern Ethiopia". Journal of Hydrology. 545 (1): 299–309. doi:10.1016/j.jhydrol.2016.12.019.
  12. Nyssen, Jan; Descheemaeker, Katrien; Zenebe, Amanuel; Poesen, Jean; Deckers, Jozef; Haile, Mitiku (2009). "Transhumance in the Tigray highlands (Ethiopia)". Mountain Research and Development. 29 (3): 255–264. doi:10.1659/mrd.00033.
  13. Sembroni, A.; Molin, P.; Dramis, F. (2019). Regional geology of the Dogu'a Tembien massif. In: Geo-trekking in Ethiopia's Tropical Mountains — The Dogu'a Tembien District. SpringerNature. ISBN 978-3-030-04954-6.
  14. Moeyersons, J. and colleagues (2006). "Age and backfill/overfill stratigraphy of two tufa dams, Tigray Highlands, Ethiopia: Evidence for Late Pleistocene and Holocene wet conditions". Palaeogeography, Palaeoclimatology, Palaeoecology. 230 (1–2): 162–178. Bibcode:2006PPP...230..165M. doi:10.1016/j.palaeo.2005.07.013.
  15. Jacob, M. and colleagues (2019). Geo-trekking map of Dogu'a Tembien (1:50,000). In: Geo-trekking in Ethiopia's Tropical Mountains - The Dogu'a Tembien District. SpringerNature. ISBN 978-3-030-04954-6.
  16. Description of trekking routes in Dogu'a Tembien. In: Geo-trekking in Ethiopia's Tropical Mountains - The Dogu'a Tembien District. SpringerNature. 2019. ISBN 978-3-030-04954-6.
  17. https://www.openstreetmap.org/traces/tag/nyssen-jacob-frankl
  18. Nyssen, Jan (2019). "Logistics for the Trekker in a Rural Mountain District of Northern Ethiopia". Geo-trekking in Ethiopia's Tropical Mountains. GeoGuide. Springer-Nature. pp. 537–556. doi:10.1007/978-3-030-04955-3_37. ISBN 978-3-030-04954-6.
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