Background

Tue, 2007-06-12 13:59 by hcroze · Forum/category:
Figure 2.  Water resources in the Amboseli ecosystem.  All indicated water courses are seasonal, as are the waterpoints indicated as dams.  Springs and boreholes are perennial but often secured from access by wildlife.

"Scarcity of permanent water is the salient feature of Amboseli’s surface hydrology; water is obviously a key limiting factor in the ecosystem. Apart from a handful of spring-fed rivulets that bubble from the northeastern piedmont of Kilimanjaro (such as Nolturesh), there are no perennial rivers in the ecosystem, only seasonal streams that flow for short periods during the rains (Fig. 2). The Eselenkei-Kiboko river drainage in the north and northeast portion of the ecosystem is highly seasonal. There is no surface runoff from the Chyulus: rainfall soaks almost on impact into the porous volcanic soils. There are also no permanent streams coming from the Kilimanjaro slopes or the catchment of Namanga Hill (also known as Oldonyo Orok, the ‘black mountain’) to the West.

"Springs and swamps. Water, which falls as rain onto the forested catchments and volcanic soils of Kilimanjaro and the Chyulu Hills, feeds through a little-understood underground drainage system and emerges at the southern margin of the basin in a number of springs that meander in channels northwards across the flat Amboseli plains. The volume of outflow determines the extent of surface water and height of the underground water table in the basin, which in turn affects the salinity of water in the rooting zones of trees...

"The springs feed an important series of west-east oriented swamps that are the lifeblood of the ecosystem: Enkong’u Narok and Lonkinya within the Amboseli National Park boundaries; then, eastward to Namelok, Kimana, Lenkati and near the Chyulu Hills, Esoitpus (Fig. 2). Thanks to the swamps, the ecosystem is today a haven for biodiversity, able to sustain the impressive populations of large herbivores, small mammals and birds, as well as the Maasai and their livestock, and high-intensity agriculture, especially in and around the Namelok and Kimana swamps.

"The extent of outflow from the springs seems to depend on variations in rainfall amount and runoff from Kilimanjaro’s forest zone. Rainfall variation may be random or cyclic, anything but constant (see below). The relationship between rainfall events and the recharging of catchments is not a simple correlation with annual amounts. There is some evidence from the Lake Victoria basin that pulses of high rainfall, such as in the late 1950s and early 1960s, which followed an extended period of lower precipitation, may have saturated catchment zones across Kenya and provided increased downstream flow for a number of years to follow (Lamb 1966, Mifflin 1991). Other possible drivers of water flow into the basin include runoff from outlying areas subject to intensive grazing and shifts in underground watercourses due to tectonic activity on Kilimanjaro. The evidence to distinguish between these factors is equivocal at best (Meijerink & van Wijngaarden 1997). It is clear, nevertheless, that prior to the late 1950s, the outflow from the basin-edge springs was relatively modest (Lovatt Smith 1997), and by 1957 both outflow and water table had begun to rise (Western and van Praet 1973) and have remained high to date (Mifflin 1991, Meijerink & van Wijngaarden 1997). "

[Extract from Croze and Lindsay (2008 in prep)]