Groundwater recharge

[KEVN]

From a TVNI email discussion I (Elise) recently got this - with good
links to very relevant scientific sources.
Groundwater recharge was a key issue in the IEK conference, and for
Kenya it will be centre stage for years to come...

Hi All,

Sorry if I am boring you but some might be interested.

This link is also relevant re groundwater in India, particularly for
those with India experience (which I don't have):
http://www.scidev.net/en/news/scientists-develop-improved-groundwater-forecastin.html
More details of the research here: http://www.ias.ac.in/currsci/apr102009/933.pdf

The term "recharge" only appears in a paper in the bibliography
(Ahmed, S., Engerrand, C., Sreedevi, P. D., Kumar, D., Subrahmanyam,
K., Ledoux, E. and Marsily, G. de, Geostatistics, aquifer modeling and
artificial recharge). Several searches later a 2007 paper by "Benoît
Dewandel, Jean-Marie Gandolfi, Faisal K. Zaidi, Shakeel Ahmed and
K. Subrahmanyam" was located: http://www.ias.ac.in/currsci/apr252007/1093.pdf
This is definitely worth reading for those interested in the use of
the VS in groundwater recharge, as it discusses the role of artificial
recharge structures on groundwater levels in that particular South
Indian geology.

The upper 10-15 metres of material has low permeability but is
underlain by a fissured layer 15-20 metres thick of high
permeability. To my thinking, the role of Vetiver hedges/terraces in
slowing the monsoonal run-off might increase the volume of water
passing through the upper layer. Each terrace could allow rapid
infiltration into its trapped sediment, but retain that water to
slowly seep into and through the upper saprolite layer.

There is discussion in the paper about the estimate of the role of dug
"tanks" on infiltration (page 1098) from which a theoretical figure
could possibly be derived for Vetiver terraces, but the proven impact
in Ethiopia seems to be better evidence. I remain suspicious of
models of catchment behaviour that rely heavily on estimates of many
parameters. At least the authors do admit that artificial recharge
structures will have to be built, although they may have serious
negative impact on water quality. They feel that the artificial
recharge structures could add 2mm to recharge on a catchment scale.
Do we have any estimates from Ethiopia on the depth of recharge
derived from the extensive vetiver plantings?

The authors conclude that if the current cropping patterns persist,
and the only change is the use of artificial recharge structures, that
230ha of the 53 Sq Km catchment will need to be converted into
recharge structures will consequent loss of that land. Some how the
VS seems a very valid answer to their groundwater problems. Maybe
someone should contact the authors?

Regards,
Don


On Wed, Apr 29, 2009 at 9:51 AM, Don Miller <donmi...@gmail.com>
wrote:

Hi All,

Check out this site: http://www.scidev.net/en/news/world-s-major-rivers-drying-up-.html

The hydrological question is - would the reduced run-off and greater
groundwater recharge resulting from widespread Vetiver planting
improve the situation, make it worse, or have little impact on river
flows? It could certainly be effective in smoothing out seasonal
fluctuations, and by improving groundwater recharge the value of wells
would increase, possibly reducing the need to rely on rivers for water
supply.

Note that the areas of greatest river flow reduction are mostly within
Vetiver's climate zone, with the exception of northern China.

Cheers
Don

--
Don Miller
Agricultural Advisor
c/- PO Box 758
Port Vila
Vanuatu
mobile: +678 7769388
donmi...@gmail.com