Upper Wahig-Inabanga River Basin



EMMA E. MELANA
Regional Director, DENR Region 7
and concurrent Regional Project
Director, INREMP

      The Wahig-Inabanga is located between 123° 43' 0" and 124° 37' 0" East longitude, and between 9° 33' 0" to 10° 12' 0" North latitude. On September 26, 1994 it was proclaimed as a Watershed Reservation under Proclamation No. 468. It is characterized with level to moderately rolling agricultural lands and rolling to mountainous timberlands and a coastal influenced area of 31,325 ha. From the Northwest bay of the island, the river basin dissects the central part of the Island, embracing a total land area of 628 km2 or 15.3% of the total land area of the Province.

      Wahig-Inabanga has been considered as the largest and most important river within Region VII due to its high potentials as source of surface water for agricultural, household, commercial, industrial and recreational uses, its significant physical features and biological resources, and its strategic location. It encompasses the large agricultural valley within the municipalities of Sierra Bullones, Pilar, Dagohoy and San Miquel. The National Irrigation Administration (NIA) in the Municipality of Pilar constructed an irrigation dam to service about 5,000 ha of agricultural lands.

      The river originates from the municipalities of Sierra Bullones and Pilar and empties into the municipality of Inabanga discharging a daily average of 1.975 million cum of water into the Cebu Strait that separates the Islands of Bohol and Cebu. This volume is enough to supply the domestic daily needs of about 637,097 households.

      Some of the issues and concerns prevailing in the area are: a) human settlement and land cultivation; b) forest and grass fire; c) illegal timber cutting; d) unclear resource use rights; e) sustainability of the watershed; f) lack of or inadequate technical/financial assistance on farmers re: agroforestry and other livelihood system; g) access to credit or financial services and social and health services; and h) provision of all-weather farm to market roads.

      The river basin is composed of four watersheds, namely: Wahig-Pamacsalan with an area of 138.89 km2, Inabanga with 139.28 km2, Dagohoy with 216.37 km2 and Danao, 133.39 km2. It is the smallest river basin under INREMP. The river basin traverses 15 municipalities that comprise around 130 barangays with a potential 22,366 beneficiary households and land coverage of 628 km2 ha covering about 15% of the Province in terms of land area. Population density within the river basin is 222 persons per km2, much lower than the provincial population density of 299 persons per km2.

      The river basin has a computed poverty incidence of 46.9%, which is much higher than the national 32.9%. Within the province, the top five poorest municipalities include Danao, Buenavista, and Ubay that are covered under INREMP.


SUBWATERSHED AREA (km2) % FROM TOTAL URB MUNICIPALITIES NO. OF BARANGAYS
Wahig-Pamaksalan 138.89 22 Duero
G. Hernandez
Jagna
Pilar
Sierra Bullones
1
1
1
13
20
Danao 133.39 21 Buenavista
Danao
San Miguel
Trinidad
Talibon
5
10
1
1
1
Dagohoy 216.37 35 Carmen
Dagohoy
Danao
Pilar
San Miguel
Sierra Bullones
Ubay
2
15
2
5
2
3
3
Inabanga 139.28 22 Carmen
Danao
Inabanga
Sagbayan
2
5
30
7
TOTAL 627.93 100.00 21 / 15* 130

* Avoided double counting of covered municipalities and barangays

      Topography and Slope. The elevation of the watershed ranges from 0 at the coastal area to 860 masl at the headwaters in Sierra Bullones. About 53% of the area have slopes of less than 18% (flat to rolling) while 12% have 18-30% slope (steep) and 35% have over 30% slope (very steep to critical slope). Of the areas classified as forest lands, 12% have slopes of less than 18%, while 88% have slopes of 18% or higher. For A & D lands, 73% have 0-18% slope while 27% have slope over 18%. It may be noted that 12,000 ha of cultivated area planted to annual crops constituting 19% of the total basin area are located in slopes of over 30%.

      Climate and Rainfall. The area falls under the 4th climatic type (Coronas), where rainfall is more or less evenly distributed throughout the year. Rainfall is deemed more than sufficient to meet the moisture requirement of most plants. The annual average rainfall is 4,598 mm (4,614 mm in Pilar, 6,485 mm in Dagohoy, and 2,682 mm in Danao). The monthly average is 383 mm while daily average is 12.6 mm.

      Land Use and Land Classification. Out of the 62,793 ha of basin area, 20,227 ha or 32% have been classified as forestland, while 42,566 ha or 68% are A&D lands. Of the 20,227 ha of forest land, only 5,880 ha or 29% are with forest cover, 9,171 ha or 45% are cultivated and planted to annual crops, 11% are grassland, 10% have shrubs and the remainder have perennial crops or wooded grassland. On the other hand, of the 42,566 ha of A & D lands, 2,919 ha or 7% are with forest cover, 35,999 ha or 85% are cultivated and planted to annual crops, 1,242 ha or 3% are cultivated and planted to perennial crops and the remaining 5% have either shrubs or wooded grassland.

      The river basin has only 14% forest cover or 8,799 ha out of 62,793 ha, of which 67% are legally classified forestlands and 33% are A & D lands. The forest cover is composed of 4,164 ha or 47% open canopy forest, 4,280 ha or 49% plantation forest and 355 ha or 4% mangrove. It is interesting to note that of the total plantation forests, 53% are in A & D lands.

      Water Resources. The whole watershed has a nine order stream which has a total of 712 streams. The total stream length of subcatchments is 657.5 km. with an average length of 0.92 km. The Inabanga subcatchment has the longest stream length with 160 km while Mas-ing River subcatchment has the shortest with 47.5 km. The average discharge of tributaries range from as low as 36,146 m3/day in Sagnap to as high as 203,564 m3/day in Malitbog. Based on the water quality standards for surface freshwater, the discharge of major streams inside the Watershed are considered suitable for domestic, irrigation and industrial uses.

      The Municipality of Inabanga has approximately 20 km of coastline from Tubigon to the Baluarte River mouth in northwest Bohol. Only a strip of mangroves are found along the estuary of Inabanga and along this strip are areas which have been converted into aquaculture ponds and utilized by the locals for nipa plantation and harvesting. The intertidal zone is characterized predominantly of mudflats with a high density of fish pens and islands with mangroves, rocky outcrops and coral reefs. The marine benthic community is characterized by a diverse yet disturbed reef affected by several factors: siltation, fishing activities of adjacent reef and a possible outbreak of crown-of-thorns. The extent of siltation in Inabanga River is observed in almost all coastal barangays. Sediments have covered the vast shallow reef flat area. In general, all sites are under the category of fair coral cover having a good potential for resource rehabilitation if properly managed.

      The Inabanga estuary provides productive habitat for invertebrates, fish, and birds including endangered species as well as spawning and nursery grounds for many species of fish, supports seagrass vegetation, shellfish beds, and nesting grounds for a variety of birds. Presently, it is also subjected to intense pressures (with the presence of fish pens, oyster farms and fish ponds), recreational uses (bathing), and non-point source pollution (laundry) from changing and intensifying land uses.

      Tree Species/Vegetation. Wahig-Inabanga River Basin is almost all farmlands with patches of grasslands, thickets and secondary forests save for some hilly areas. On the hilly portion as well as flat lands are small patches of coconut plantations where in some cases small trees, brushes and weeds are left to grow among the coconuts. Other areas such as along feeder roads, boundaries of adjoining properties, and land not being used for planting short-term crops such as rice and corn are planted to fast growing species like Gmelina arborea, Acacia mangium, Acacia auriculiformis.

      Biodiversity Assets. The watershed contains about 14%21 of the Rajah Sikatuna Protected Landscape, one of the priority sites for conservation in the Philippines (KBA 92). In a factsheet prepared by Bird International (2009), it is reported that this protected landscape has most of the significant forest of Bohol and characterized by rolling hills with remnant natural forest on steep limestone terrain surrounded by plantation forests, deforested hills and grassland. Among the bird species found in the park are three species endemic to Eastern Visayas: the Samar hornbill (Penelopides samarensis), Visayan hornbill (Penelopides panini), and yellow-breasted tailorbird (Orthotomus samarensis). Furthermore, it is also reported that 10% of the park has been converted to agriculture land. Current threat to the park includes land conversion (kaingin), collection of non-timber forest products, and hunting.



      Infrastructure. The Province has a good network of national, provincial, and municipal roads. All towns or even the farthest are accessible by land transportation. Wahig-Inabanga is linked to the rest of Bohol through the national highway that originates from Tagbilaran and is paved at different segments with concrete and gravel. The highway branches into the river basin and connects all the Municipalities within the river basin reserve. Villages are accessible by barangay roads and trails through motorcycles only, thereby contributing problems in transport of materials, agricultural inputs and outputs during rainy seasons.

      Two major road sections, Tagbilaran North Road (TNR) and Tagbilaran East Road (TER) are also being improved under the Arterial Road Links Development Project. This would traverse through several municipalities including those within the Wahig-Inabanga River Basin.

      NIA 2006 data shows that Bohol's potential irrigable area is about 30,090 hectares with a total service area of 14,388 hectares equivalent to 48% irrigation development rate. The biggest national scheme in the province is the Bohol Irrigation Project (BIP) covering the 6 municipalities of Alicia, Dagohoy, Pilar, San Miguel, Ubay and Trinidad all within the river basin with main source of irrigation water supply from Wahig and Pamacsalan Rivers at the municipality of Sierra Bullones. Aside from BIP, the river basin area also has an existing NIA assisted communal irrigation schemes with an aggregate service area of about 2,363 hectares with several schemes proposed for rehabilitation and improvement under the NIA development program.

      In the municipality of Pilar, the Lumbay Hagdanan Irrigators Association has obtained water rights for Bagon-an Creek to be used for communal irrigation system (CIS) in barangay Lumbay. Communal Irrigation Systems are similarly present in other municipalities.

      About 61% of the province's total HHs is currently provided with safe drinking water from Levels I, II and III systems. Levels I draw its source from sealed open dug wells while Levels II and III are from natural spring development and deep well sources. However, based on the 1993 Philippine National Standards for Drinking Water, some of the water coming from springs and deep wells are. Cadmium and lead contents of the water far exceed standard values.

      Agriculture. The most common problem as regards agriculture revolve around the issues of small farm parcels, barren soil, unfavorable climatic conditions, the cost of production inputs, pest and diseases and soil degradation among others. In terms of marketing, the most glaring problem is farm to market roads. The only regular transport towards the inner barangays in the river basin is through the 'habal-habal' or motorcycle. Products are damaged during the travel. Low product prices and price fluctuations similarly are identified constraints.

      Quarrying. It is estimated that 65% of the province is covered with limestone of which Garcia-Hernandez, one of the municipalities within the watershed, has the biggest quarry site.

      Tourism. Tourism and recreation is alive within the river basin. Recreational activities at present are confined to cave exploration and nature appreciation. The water reservoir in Pilar is a growing attraction to both local and visiting tourists for picnic and boating. It is also known to contain significant natural geological features, such as caves and chocolate-shaped hills that are highly potential for ecotourism attractions. Also, the Watershed still contains significant forests that are productive habitat for a good number of significant wildlife species in the Island, such as the tarsier, flying lemur, fruit bats, tariktik, and others.