Evaluation of the Contribution of Roadside Ditches to Non-Point Source Pollution in the Bengawan Solo Watershed, Central Java, Indonesia

Abstract:

Bengawan Solo is the largest river in Central Java, Indonesia and is facing increasing pressures in the fast-developing region which is home to more than six million people living in the basin. However, unlike other watersheds that face issues of water scarcity, water availability is not its main concern. While water is relatively abundant, other issues prevent accessibility to clean water, such as non-point source (NPS) pollution. Recent research has demonstrated the key role that networks of roadside ditches play in water pollution as well as flooding in watersheds of the Northeastern However, roadside ditches have been previously unaccounted for as contributor to the NPS pollution in Indonesian watersheds.

We have been evaluating the contribution of roadside ditches to the Bengawan Solo river through Google Earth Pro and ArcGIS mapping. Length of ditches and number of outlets into streams are being quantified in a subbasin of the river. Land adjacent to ditches is being mapped to estimate area and land use of basins contributing to ditches to infer input as agricultural, industrial or residential runoff. Preliminary results from initial mapping reveal that these ditches are a network connected to watersheds that has been largely overlooked and can be used as a solution to controlling pollution inputs. Understanding the extent of contribution of roadside ditches will assist in future management strategies in an abundant watershed that ironically lacks accessibility to clean water. An outreach program has been initiated with local governments to increase awareness. Management of these ditches can facilitate the reduction of sedimentation and pollution, help prevent flooding and even reduce the potential for water-borne disease outbreaks.