Hydrogeological interpretation is based on the inventory of well records from Bohol collected during water sources survey in 1998 and information on geological formations from geologic maps and related literature. The municipality of Valencia is covered by four (4) sedimentary rock formations namely, Carmen Formation, Sierra Bullones Limestone, Maribojoc Limestone and Quaternary Alluvium.
Sierra Bullones Limestone, which caps the mountain range in southeastern part of Bohol, has the largest outcrop area at 58.04 sq. km. or 44.85% of municipal area. This unit is massive, cavernous, fossiliferous and marly in places. Becuase of its location in the mountains and high elevation, this formation does not have groundwater development potential. However, due to high permeability, infiltrated water is drained toward lower areas where it would resurface in form of springs. Carmen formation, which has a large extent over the municipality (49.24 sq. km. or 38.05% of the municipality), is not considered potential source of pumpable groundwater because of widespread occurrence of shale, sandstone, siltstone and marl of low permeability.
Maribojoc Limestone covers 17.93 sq. km. or 13.86% of the municipal area. The limestone is highly coralline, bedded to massive, soft, chalky, non-compact and marly. Limestone exhibits numberous sinkholes, caves and caverns, which are product of chemical weathering of carbonate rocks, characteristic for karstified terrain. Consequently, run-off occurs only during intensive rainfall, otherwise most of the effective rainfall infiltrates into underground. This formation has a good potential for ground water development due to its very high permeability. When marls and clay layers are intercalated within Maribojoc limestone, springs and artesian conditions occur. A small portion of 4.19 sq. km. or 3.24% of the municipal area along the coast is covered by Quaternary Alluvium, consisting of mud, clay, silt, sand gravel and coral and cell deposit along shore, swampy areas and beaches. Usually, this formation has a good groundwater potential however, its very limited outcrop and area does not hold any significant groundwater potential for the municipality.
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Topic: Hydrogeology (Read 1198 times)