El desarrollo legal: La Ley Reguladora de las bases de Régimen Local

The city of Tagbilaran is located within the Tagbuane River basin, which has an area of 137.28 km2

and also comprises the municipalities of Corella, Sikatuna, Cortes and Loboc. Surface water runoff for the Tagbuane river basin is estimated as being 294 mm per year per m2; the average surface runoff for the city area is estimated as being 23,522 m3 per day (Province of Bohol and SWECO, 1999a). There are no natural bodies of freshwater in Tagbilaran other than small ephemeral rivers and creeks draining into the sea, which indicates that almost all effective rainfall likely infiltrates underground (Province of Bohol and SWECO, 1999a). Springs are

common, including some that are very large with high discharge rates, with springs occurring along the coastline discharging groundwater to the sea.

Tagbilaran is entirely dependent on groundwater for its water needs. The use of groundwater in Tagbilaran mirrors practice elsewhere in the Philippines where groundwater is used for domestic and industrial demand while water for irrigation is provided by surface water, and illustrates its significance in urban environments (JICA, NWRB, DPWH and Republic of the Philippines, 1998; NEDA, 2002). In this regard, groundwater represents an important water source in Tagbilaran, Bohol and the Philippines, particularly in light of increasing water demand.50

Groundwater storage for the entire country is estimated at 1,222,896 million cubic metres with an annual recharge of 31,694 million cubic metres (JICA, et al., 1998; NEDA, 2002). Contrastingly, it is estimated that the total run-off in river basins is approximately 455 million cubic metres.

Given the importance of groundwater for Tagbilaran’s water needs, the geology underlying the city is significant in terms of groundwater storage capacity, flows and the potential for contamination. Tagbilaran’s geology is karst limestone51 dating from the Pleistocene epoch. Karstic features such as sinkholes and low-lying areas with hill topography are characteristic. Karst is formed through the dissolution by groundwater of soluble carbonate rocks including limestone (calcium carbonate) and dolomite (magnesium calcium carbonate) to form a subsurface drainage system. Rainwater becomes acidic as it picks up carbon dioxide from the air and from percolation through soils, largely as a result of biological activity, which forms limestone solution when it comes into contact with calcium carbonate. Water follows lines of weakness such as fractures and faults forming channel ways and conduits as it dissolves the rock. Sinkholes and caves are common characteristics in karst environments. Aquifers in karst environments are capable of providing large supplies of water; however, flow patterns are unpredictable and highly variable when compared to aquifer systems in other hydrogeological environments (Foster, et al., 2000; Foster, et al., 1998; Foster, 2001; Foster and Chilton, 2003; Tuinhof, Dumara, Foster, Kemper, Garduño and Nanni, 2003; Urich, et al., 2001).

Karst aquifers differ from aquifers in other hydrogeological environments in a number of ways: first, water is not uniformly distributed below the surface; second, much groundwater movement is through caves and conduits below ground and the flow rates can be very rapid; third, groundwater movements tend to be complex and direction and paths for travel are difficult to predict from the surface; and, fourth, the ease of water flow and lack of natural filtration make groundwater in karst environments very vulnerable to groundwater pollution (Heath,

50

Water demand nationwide is expected to grow from 43,400 million cubic metres per year in 2000 to 88,400 million cubic metres per year by 2025 (JICA, et al., 1998).

51

The geology in this area has been classified as Maribojoc limestone (Province of Bohol and SWECO, 1999a).

1983). The heterogeneity of subsurface characteristics in karst environments means that there is the possibility for considerable spatial variability such that a well with prolific quantities of water could be adjacent to one that is entirely dry (Dubash, 2002).

A key source of hydrological data for Tagbilaran is the Philippine Water Master Plan, which has determined that the limestone in the area is not a good medium for retaining water (JICA, et al., 1998). According to this source, groundwater in Tagbilaran flows via conduit and cave systems and, therefore, flow velocities more closely resemble surface water with reservoirs and recharge areas corresponding to sinkholes and depressions which are interconnected via cave and channelling systems. Flow routes are subject to change as a consequence of dissolution enlarging conduits, caverns and caves over millions of years, as well as through other natural process such as subsidence, sinkhole collapse and tectonic activity. Anecdotal reports support the effect of tectonic activity on Tagbilaran’s hydrology, with reports of changes in the amount of discharge from springs and flow patterns after earthquakes. In addition, coastal aquifers are at risk of over-pumping causing groundwater reservoirs to reduce and the water table to fall, which can alter groundwater flow-directions and lead to saltwater intrusion (Collin and Melloul, 2001). While there have been attempts to document the hydrological characteristics in Tagbilaran, as discussed later in Section 4.2, there are deficiencies in data and knowledge because of the difficulties posed by karst environments in obtaining comprehensive information.

Tagbilaran has also benefited from several overseas consultancy missions engaged in documenting the hydrological characteristics of Tagbilaran and the rest of the province at provincial, municipal and barangay levels. In 1998, an inventory of water resources in Bohol was undertaken jointly by Swedish Consultants SWECO and the Provincial Planning and Development Office (PPDO) referred to as the Water Supply, Sanitation andSewerage Sector Master Plan for Bohol Province (BW4SMP). This project followed on from earlier studies undertaken in the early 1990s by JICA and AIDAB that sought to determine water sources, quantity and quality across the Province. The BW4SMP produced reports for Tagbilaran and each of the 47 municipalities in Bohol down to the barangay level and covered physiographic, socio-economic and institutional aspects related to water resources and their management in the province.

A number of assumptions were made in the formulation of the BW4SMP because of limited availability of information about the groundwater system in Tagbilaran; therefore, a degree of uncertainty exists.52

The water table in a karstic region is often difficult to define in

52

These assumptions are made explicit in the BW4SMP report and relate to calculations made in terms of determining the water level, runoff, infiltration and evaporation. The veracity of some of these assumptions was questioned by an engineer with whom I spoke on several occasions.

part because cave systems and conduit flows give rise to a complex subsurface drainage system. Water could be perched above the water table where there are surface depressions or the water table could be discontinuous because of the heterogeneity of the limestone. Analysis of the standing water levels in wells in the city indicates that there are two aquifers underlying Tagbilaran; a shallow aquifer and a deep one. Water quality is generally good, although some wells have salty water (City of Tagbilaran, 2001; 2003; Johnson, 2003; Province of Bohol and SWECO, 1999a)

Projects such as the BW4SMP form the basis for determining the location of pumping stations, quantities to be abstracted, and planning and management of water sources across the Province. This is in lieu of comprehensive studies examining the groundwater regime in Tagbilaran. Georesistivity surveys have also been undertaken at various times to determine how much water is available and where. Representatives from the waterworks utilities reported that these findings have also been used to guide the government in planning for the development and management of water including locating sites for pumping stations (WW#2; WW#3).

Characteristics such as those described above give rise to uncertainty in managing karst groundwater resources. Approaches to groundwater management in Tagbilaran in the past have failed to adequately take into account the complexity of the hydrological system or the factors which adversely impact groundwater resources. For instance, saltwater intrusion in Tagbilaran was noted in the study undertaken by Travaglia, Peebles, Bate and Ferrer (1987) as well as by AIDAB and JICA in the early 1990s.53 Considering the significance of groundwater as the primary source of water for domestic consumption, and forecast increases in demand as a consequence of population growth and changes in consumption patterns, efforts to secure water supplies and prevent for contamination in the city are, therefore, needed. In the next section I outline some of key factors affecting groundwater recharge in Tagbilaran and, as a consequence, the amount of water available for urban water supply.