Page 85 - Arabian Studies (V)

Water Resources ancl Agriculture in Qatar 75
and variable rainfall and an aerial view of the peninsula will
perhaps convince the observer that the country is entirely devoid of
vegetation. Six types of plant community have however been recog­
nised (Obeid, 1975) and these repeat themselves wherever similar
soil and water conditions occur. The six community types are (1)
Coastal sabkhah, (2) Coastal sand, (3) Rawdah depression, (4)
Sand dune, (5) Acacia tortilis and (6) Ziziphus nummularia. The
plant communities of the sibakh and coastal sands are predomi­
nately halophytes (Halopeplis perfoliata, Zygophyllum Cocci-
neum). The rawdah community type is confined to the colluvium
depressions of the same name with mixed and pure stands of A.
tortillis (.satnur), Z. nummilaria (sidr) and Lycium shawii (‘awasij)
forming the permanent feature of the landscape and the most
outstanding vegetational feature of Qatar. However there is consi­
derable variation in floristic composition of these depression
communities. Those of the northern half of the country have
deeper soils whereas, as one moves southward, these have become
partially infilled with aeolian sand and exhibit a different vegeta­
tional pattern. The density of vegetation is also greater in the
depressions of the south where the sand has the effect of inter­
cepting storm run-off and thus allowing a denser cover of Acacia-
Ziziphus-Lyciwn association with Fagonia indica as the dominant
ground species. The A. tortillis community type also occurs as pure
stands in habitats outside the depressions, particularly along dry
watercourses and, in contrast to its co-dominant of the depressions,
Z. nummilaria, is not found outside these and is often present as
pure stands in the depressions of southern Qatar.

5. Hydrology and Hydrogeology
There is no permanent surface water in Qatar. Direct and indirect
recharge from rainfall to groundwater is the sole natural water
resource of the country. Two thirds of the land surface is made up
of some 850 continguous depressions of interior drainage with
catchments varying from as small as 0.25 km2 to 45 km2 of a total
aggregate area of 6,942 km.2 and, while direct recharge from rain­
fall undoubtedly takes place during very rare heavy storms, the
major recharge mechanism is an indirect one through run-off from
the surrounding catchment and ponding in the depression floor. Of
this, a proportion is evaporated and the remainder recharged to
groundwater through the shallow rawdah soils. Run-off observa­
tions show that surface run-off may vary from 45 per cent as a
result of high intensity storm to 18-20 per cent from average storms
above 10 mm/day. Of the amount reaching the depression 70 per