Bohol, the tenth largest island in the Philippines, is one of the country's most economically backward regions, with more than 80 per cent of the population dependent on agriculture. Poor land-use practices have caused soil erosion and runoff, leading to a decline in agricultural productivity. Bohol's fisheries and coastal mangroves have also been affected by these land degradation problems, as the quality and quantity of water in the rivers decline.
One of the most important sources of water for agriculture and domestic use in Bohol is the Inabanga watershed. The Inabanga watershed is the largest watershed in Bohol Island. There are plans to use the Inabanga River to provide the domestic water supply to Cebu, the Philippines' second largest city. The river is also necessary for planned agricultural and economic developments in Cebu. It is thus important to protect the Inabanga River; however, there is currently no quantitative information on soil erosion and runoff, and how these factors affect the quality and quantity of water in the river.
This project is providing information needed to plan strategies for reversing damage to the land and water resources, and restoring agricultural productivity, to assist in developing strategies for reviving agricultural productivity in the Inabanga watershed in Bohol Island, Philippines, whilst protecting soil and water resources.
The project team first analysed and described the current state of the natural resources in the Inabanga watershed. The approach involved data gathering from geographic information systems (GIS) as well as interviews with farmers, community groups, and local and national government and non-government organisations. The researchers gathered data on land characteristics, water use and water resources, and identified any problems associated with these resources. They could then link their information with satellite imagery to develop a database for pinpointing soil and water resource problems in the watershed.
The initial results enabled the team to decide which land-use practices would be subjected to more detailed examination over the following two years, to determine their effects on soil erosion and runoff. The team also collected information on the distribution of water from the Inabanga River to sectors such as agriculture, industry and domestic water supply, along with demographic information about farmers for use in analysing socioeconomic issues and their impact on agricultural water management.
The team completed maps showing estimates of current land-use areas that included six major agricultural crops (irrigated rice, rainfed rice, corn, cassava, coconut and oil palm) and forestry/grassland areas. The land-use cover percentages were: agriculture usage 52%; grassland and shrub land areas 33%; woodlands 12%; wetland areas 1%; miscellaneous/built-up areas 1%. Watershed maps developed showed the area in three soil-depth classes, slope maps in six different slope percentage classes (0-3, 3-8, 8-18, 18-30, 30-50 and above 50) and a general erosion map in five different classes. Maps were produced as both stand-alone maps and as GIS data-layers.
Technical information gathered was incorporated into a GIS framework and database to support better decision-making via data and trend evaluation and modelling, for application to a wide variety of watershed management decision-making issues. Cropping and land-use suitability was assessed in the watershed pedo-ecological zones with respect to soil type, with further evaluation incorporating specific agriculture practices, water source and slope characteristics. Local advisory teams provided technical assistance to support ongoing transfer of education and training to sustain good agricultural practices, conserve soil and water resources, improve farming practices and increase farm income.
Data gathered at the seven experimental erosion and runoff sites and three water sampling sites helped determine runoff volume, water quality and soil loss under a wide variety of rainfall and cropping conditions experienced through the year. Data for nitrogen and phosphorus losses were also determined. The sites include the following land-uses: agroforestry, woodland, cassava/corn, grassland, rainfed rice, irrigated rice and oil palm. Compiled in GIS format and linked database, the data provide a rich source of information for planning agencies and NGO groups when making presentations during farmer/community training activities.
A comprehensive dataset addressing agro-socio-economic issues in the watershed has been completed. It was compiled from farm surveys across the watershed - 932 households from 114 barangays of 14 municipalities in 2000 and another 126 household in five municipalities in 2003. The dataset also included interviews and collected data from farmer cooperators at five project sites. A picture emerged of high poverty levels, rising unemployment and low per capita income. Farm productivity, with the exception of irrigated rice, fell below the national average.
Alternative cropping scenarios and present/future water management practices were considered in developing strategies to reduce sediment transport. Through planned demonstration farms and learning centres, the team aims to create an enabling environment for stakeholders and others to protect and preserve watershed resources.
The project introduced scientific methods and instrumentation to deal with soil and water resources research at a watershed scale rather that the conventional plot scale. These technologies and approaches have bolstered local capacity to monitor and evaluate data, yielded information to produce maps and database sets, and lifted capacity for predictive evaluation of management options via modelling based on empirically derived data.
Links:
[1] http://www.aciar.gov.au/country/Philippines
[2] http://www.aciar.gov.au/programarea/Land and Water Resources