Water Table Level

[Hydrologist, Dr. Mike Lane, was asked to comment on AERP water table measurements and the Amboseli hydrology question in general. He wrote...]

At 11:11 02/12/2003 +0300, Aquasearch Ltd wrote:

Harvey, Cynthia, Joyce ....

Typo: in last sentence of last paragraph in my email of yesterday I should have written " ... the Trust or the Project".

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Playtime

First shot at analysis shows that generally well water levels (metres below bench mark):-

a) correlate well with sunspot number (gross climatic variable)
b) correlate fairly with adjusted rainfall (Altmann et al 2002) (local climatic variable)
c) correlate poorly with oxygen 18 (from Indian Ocean coral carbonates: Cole et al 2000), pretty much what one would expect (near-recent to recent climate change)
d) correlate poorly with Indian Ocean sea surface temperature (Malindi) (Cole op cit), but there is only a short annual time series terminating in 1989 (near-recent to recent climatic change)

Nothing quantitative so far, but what there is immediately poses numerous questions, of which the following are perhaps the most germane: -

i) what age is well water (i.e. immediately local recharge, or lateral recharge)?
ii) how has water quality changed with well water levels, and over time?
iii) is there any correlation between broader catchment land use change and water level?
iv) how much water is abstracted per unit time, and has this changed significantly over time?

In respect of i) above this calls for water quality analyses (both major and trace chemical, and exotics such as noble gas concentration, 3H, 13C/14C or CFCs), and is unlikely to have been carried out.

In respect of ii) above, has water quality (gross parameters like salinity, specific conductivity, pH, alkalinity etc ...) been monitored? Just curious!

In respect of iii) above I have yet to develop this further. This will possibly turn out to be the critical variable over historic time, and will probably call for some pretty heavy space imagery analysis (cover type mapping can take advantage of a host of techniques - false colour IR, textural change, synthetic aperture radar, thermal mapping etc ...) but of course this is limited to recent history. Palaeoclimate reconstruction is likely to be important for historic cover-type mapping.

In respect of iv) above, does the camp keep records of pumping times or costs, periodicity, abstraction volume etc ... from these wells? Experience elsewhere in EA suggests probably does not - but then again, it is a scientific camp rather than any other type ...

More curiosity
Do you know whether any research body has undertaken analysis of cores from the Amboseli lake bed or other permanent water body (the Simek delta seems an obvious site) for biogenic opal, palynology, environmental isotopes (18O and 2H) or other palaeoclimatic parameters? I think I would have heard if someone has (palaeoclimatic reconstruction being a passion of mine), but I don't spend as much time in the Amboseli area as I would like!

I think it will be vitally important to reconstruct palaeoclimate - or perhaps more accurately, historic climate (past 300 years or so) - in describing and quantifying the variables and assessing the dimensions of change in water resources availability over time. This is important if resources availability projections are to be made (I think they should: the Amboseli ecosystem is acutely sensitive to water availability).

The decline in Kilimanjaro icecap area/volume (Thompson et al 2002 and many others) may affect recharge to deep aquifers (i.e. those exploited by Embarinkoi, Kitenden, Maarba and Naiperra: and the major spring units within and east of the Park), though the little I know of this hydrologic system suggests that rainfall at middle elevations (2,500 - 3,500 m amsl?) is more likely to be the critical variable. I'll see if I can search out (farming) rainfall records for the Shira Plateau area - they will be useful, and Tanzanian rainfall data are surprisingly frequently available, back as far as the early part of the last century (but much more limited from the mid/late 1970s).

There is a possible research project - or programme - here. It may be possible to obtain funding from the IAEA (International Atomic Energy Authority) for isotope/tracer work, though this would have to go through Government. There are relatively few Kenyan researchers active in the isotope field, but we have some good ones (Eric Odada and Dan Olago at UoN: Anthony Gachanja at MAJI House). So far as I know I am the only private sector isotope bod around - its a pretty small field and we do not use it properly in Kenya (if at all). I used 2H and 18O in assessing recharge to the Merti aquifer in north eastern province in my M.Sc. thesis in 1995: unsuccessfully, as it turned out, but subsequent research shows it to have been the right approach.

I'm already in the process of drawing up a broad study proposal for a basin-wide water resources availability study ( building on some throwaway suggestions made to the Kitirua Trust in early 2003). I'll develop the themes made above in this.

Any comments so far?

Cheers,

Mike.

Altmann J, Altmann SC, Altmann SA & Roy SB, 2002: Dramatic change in local climate patterns in the Amboseli basin, Kenya. Afr. Jour. Ecol. 40, 248-251.
Cole JE, Dunbar RB, McClanahan TR & Muthiga N, 2000: Tropical Pacific forcing of decadal variability in the western Indian Ocean over the past two centuries, Science 287, 617-619.
Lonnie LG, Mosley-Thompson E, Davis ME, Henderson KA, Brecher HH, Victor S. Zagorodnov VS, Mashiotta TA, Lin P-L, Mikhalenko VM, Hardy DR & Beer J, 2002: Kilimanjaro Ice Core Records: Evidence of Holocene Climate Change in Tropical Africa. Science 298, 589-593.