Tana river delta, Kenya


 

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The Tana River is the longest in Kenya being over 1000km long and it has a catchment area of 95,000 km² (or 120,000 km² according to other estimates), starting on Mount Kenya and entering the ocean in northeastern Kenya near Kipini.

An average of 4,000 million m³ of freshwater are discharged annually with peak flows occurring between April and June and a shorter high flow period during November/December. The Tana River also discharges some 3 million tonnes of sediment per year. It enters the ocean about halfway between Malindi and Lamu, near Kipini, into Ungwana (Formosa) Bay. However, before it does, and about 30km upstream, it gives off a branch which leads to the complex of tidal creeks, flood plains, coastal lakes and mangrove swamps known as the Tana Delta. The Delta covers some 1,300 km² behind a 50m high sand dune system which protects it from the open ocean in Ungwana Bay.

The current mouth of the river near Kipini is not its natural mouth but used to be the estuary of a smaller river, the Ozi. The mouth of the Tana was located about 30 km. southward, now called Mto Tana. In the 1860's, a channel was dug to connect Belazoni (along the Tana river) to Kau (on the Ozi) and after a particularly heavy flooding event at the end of the 19th century, the river broke through and this artifical connection widened and became the principal mouth - the Mto Tana only functioning during periods of flooding. In the 1960's, a new breakthrough occured in the southern delta, whereby the southern delta was now also connected to the ocean at Shekiko. This part of the delta now consists of a network of tidal creeks, with extensive mangrove cover interspersed with seasonally flooded grassland dotted with palms and Acacia. Some of the creeks have been cut off from the Tana river, but the most western creek, Matolo, still has a functional connection to the main river course.

The high sediment loads carried by the Tana and Sabaki river are partly attributable to poor land use practices in their upper catchments which are important agricultural lands.

 
The Tana delta has mangroves along the main river course between Ozi and Kipini (including large areas with tall Heritiera littoralis - about the only place in Kenya where these are found) and in the tidal delta south of the main river where mangroves (dominated by Avicennia marina, but Rhizophora mucronata, Ceriops tagal, Bruguiera gymnorrhiza, Xylocarpus granatum, Sonneratia alba are also found). Although their numbers have declined considerably, this area is still home to crocodiles, hippos, elephant, ...
 
Sampling was carried out in April 2004 along the salinity gradient of the Tana river (from around Ozi and into the plume at sea where much of the salinity gradient was found) and in the tidal mangrove creeks in the southern delta. Overall, surface water was sampled at ~65 locations for in situ measurements of t°, salinity, pH, and %O2, and samples taken for later analysis of total alkalinity (and DIC & pCO2), TSM, POC, DOC, d13C-DIC, d13C-POC, d15N-PN, d18O-DO, chlorophyll-a, Ca, Mg, Si, NO3, PO4, ... (part of these are carried out by the Chemical Oceanography Unit, University of Liège). Porewater samples were collected from an additional 7 locations in the intertidal mangrove zone.
 

Murky waters of the Tana river, near Kipini (Kenya). Mangrove
 vegetation dominated by Avicennia marina and Heritiera
 littoralis
. Hippos pop up their heads every few minutes
 along this stretch.

Tana river, upstream towards Ozi. Terrestrial floodplain
 forests replace the mangroves along the river banks.

Mto Tana - the former river mouth untill late 19th century or early
 20th century, which has now become a very shallow and
narrow channel.

Shekiko - the site where the water broke through the sand dunes
 in the 1960's now the main connection between the southern
delta and the ocean

Matolo creek - still with a functional connection to the main
 Tana river

View over the mangroves in the delta from the sand dunes in Shekiko

   
 
Literature on the Tana delta :

 

Brakel WH (1984) Seasonal dynamics of suspended sediment plumes from the Tana and Sabaki rivers, Kenya: analysis from Landsat imagery. Remote Sensing of Environment 16: 165-173

Andrews P, Groves CP & Hornes JFM (1975) Ecology of the lower Tana river flood plain (Kenya). Journal of the East Africa Natural History Society and National Museum, no. 151 (31 pp.)

Maingi JK & Marsh SE (2002) Quantifying hydrological impacts following dam construction along the Tana river, Kenya. Journal of Arid Environments 50: 53-79

Ferguson W (1995) The mangrove ecosystems in the Tana river delta. Unpublished report of the environmental impact assessment of hydropower dams in the Tana River (Grand Falls and Mutonga dams).

There are plenty of papers that deal with the more upstream regions of the lower Tana - most of them are focussed on the floodplain forests and the Tana River Primate Reserve. Also two recent papers on this area are :

Allison EH, & Badjeck MC (2004) Livelihoods, Local Knowledge and the Integration of Economic Development and Conservation Concerns in the Lower Tana River Basin. Hydrobiologia 527: 19-24, and :
Terer T, Ndiritu GG, and Gichuki NN (2004) Socio-economic values and traditional strategies of managing wetland resources in Lower Tana River, Kenya. Hydrobiologia 527: 3-14.

For those who want to dig somewhat deeper:

Chanler, William Astor: Through jungle and desert; travels in Eastern Africa. The first edition was printed in London by Macmillan and Co., 1896.
There is a reprint by Elibron Classics, printed in 2001. Contains a fold-out map of the Tana district.

Krapf, J.L  : Travels, researches and missionary labours during an eighteen years' residence in Eastern Africa; with an appendix respecting the snow-capped Mountains of Eastern Africa, the sources of the Nile, the languages of Abyssinia and Eastern Africa, by E. G. Ravenstein.
First edition printed in London by  Trübner and Co (1860) (there is also a print of the book in Boston from the same year, but without the illustrations) - again, not easy to find. There is a reprint from 1968 by Frank Cass (London), but it is also out of print.

Denhardt C &  Denhardt G (1884) Bermerkungen zur Originalkarte des unteren Tana-Gebietes. Zeitschrift der Gesellschaft für Erdkunde [Berlin]19; 122-160, 194-217.
These were the 2 famous German brothers who made a deal with Sultan Ahmad of Witu in 1895 to make 'Wituland' a German protectorate. See the following article for a short background.

Ravenstein EG (1890) Mr. J.R.W. Piggott's Journey to the upper Tana, 1889. Proc. R. Geogr. Soc. 12: 129-136.
Not much on the lower Tana river, it does make a good read.

Sampson HC (1933) The Tana river region of Kenya Colony. J. Roy. Soc. Arts 84: 92-111.  A certain Worsley writes about the Tana delta as a comment : "Altogether, it is not an attractive region; I was glad to get out of it" !

Gedge E. (1892) A recent exploration, under captain F.G. Dundas, R.N., up the river Tana to Mount Kenya. Royal Geographical Society, London, 21 pp + folding map.
Has a brief description of the area around Mto Tana - now a small mangrove creek but in those days the Tana river mouth. He describes the presence of large areas of mangroves, and states that this is one of the main areas from which mangrove poles are exported to Lamu. This likely implies that there used to be a lot of Rhizophora mangroves in the area - which is no longer the case.

Kirkman JS: Ungwana on the Tana (Paris, Mouton & Co., 1966). This is an in-depth report on the excavations of the Ungwana ruins, just outside Kipini. See here for an introduction to the historical sites around the Tana delta

 
Links to relevant internet sites :
Tana delta Factsheet (BirdLife International) has some information on the ecological importance of the area and on conservation issues.

Tana Delta Camp : for people interested in visiting the area, this is just about the only place to stay in the southern part of the delta - magnificently situated on the slope of the dunes, overlooking the ocean and the mangrove creeks (photo on the lower right above is taken from there).


Last update : December, 2004

http://www.vub.ac.be/ANCH/CV/tana.html