Information on the location and availability of groundwater resources in the seven countries of Central American is both limited and variable. For example, while understanding is somewhat greater in Nicaragua and Costa Rica, in Belize existing aquifers and their annual discharge have hardly been studied. Still general information is available for most countries and is summarized in Table 6.2 and general patterns are discussed here.
In general terms, the higher parts of the watersheds in Central America are underlain by volcanic aquifers. In the lower river basins and inland valleys, aquifers of recent alluviums predominate, whereas in the middle parts of the river basins the aquifers are a mixture of volcanic materials, colluvial alluvials and, of lesser importance, aquifers of sedimentary rocks (Losilla et a/., 2001). Although important alluvial aquifers do exist throughout the region and some important sedimentary rock aquifers are found in Honduras, Guatemala and Belize, of particular importance to groundwater use are the highly porous soils throughout the Pacific volcanic chain that permit very high levels of rainwater infiltration to recharge the local aquifer systems (GWP, 2005). Their presence has been important historically for attracting settlements and population concentrations in the region's Pacific watersheds where, in most cases, the springs and eventual pumping from local wells have met the demand for water. Volcanic aquifers now provide potable water for most major Central American cities including Guatemala, Tegucigalpa, San Salvador, Managua and San Jose.
Unfortunately, the volcanic aquifers consist mainly of interstratifications of tuffs, gaps and quaternary as well as some tertiary lava, which present high permeability and fissure flows. In many cases, these make the aquifers highly vulnerable to human contamination from the cities they help to support. The heterogeneity of these aquifers, with differential horizontal and vertical flows, also makes them quite complicated to study and therefore to manage.
In general, the recharge of the main aquifers in Central America is accomplished by rainwater infiltration and to a lesser degree by a connection with surface water and excess of irrigation water application.
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