Watershed Management for Honiara Catchments
Photographs by Patrick Pikacha
Article by Patrick Pikacha, Myknee Sirikolo, and David Boseto, Ecological Solutions, Solomon Islands Community Conservation Partnership, and Solomon Islands National Herbarium
Published May 1, 2014
Recent heavy rains and floods around Honiara and Guadalcanal almost two weeks ago have highlighted a number of pertinent issues in regard to watershed management and mitigating the effects of storm water flow in the future.
Watersheds refer to areas where rainwater discharges from upper more elevated areas into lower lying areas, before entering a single water body such as a river, stream or wetland before arriving at the ocean. Times of extreme precipitation like last weeks deluge quickly increases surface water at flat and impermeable areas and can even intersect watershed boundaries. We saw this briefly during the rains between Lungga and Alligator creek when water crossed boundaries and almost joining up. Storm water in the city’s smaller watersheds also overflowed inundating low-lying areas.
Why focus on Honiara’s watershed
There are three main watersheds that drain into Honiara City and it’s surrounding suburbs, namely Matanikau and Lungga River, and Kongulai with its network of streams.
When planning occurs from a watershed perspective things may appear a little different. As watershed functions and processes are interrelated, it is not logical to plan from a single project or management position. For example, it would not be logical to plan each building and site along the Matanikau River separately. Rather, it would be more useful to look at the landscape and watershed and consider landscape linkages such as slope, flood inundation, water level, pollution etc. We would like to suggest a few specific alternatives here.
1. Our present land management decisions for project development along the Matanikau River are often approved on a project-by-project, or jurisdiction-by-jurisdiction basis. And even the Chinatown buildings along the river violate town-planning regulations by connecting household sewers directly into the waterway polluting the river. Further up the river, development is completely random with no systematic strategy to appropriate town planning. “Development” appears to be basically every man for himself! Consequently a singular approach to development fails to recognize the critical cumulative effects of watershed functions and systems. Furthermore this singular approach to development creates vulnerability for residents who occupy riverbanks and even coastal shorelines. This can easily be resolved if residents were relocated, and the riverine boundaries be converted to green parkways or green corridors. These corridors could act as buffers between residential and exposed river boundaries.
2. The easiest and most effective technique of reducing the impacts of storm water overflow is to regulate the quantity of paved surfaces, which comes with development, maintain drainage systems, and reserve as much as possible the natural landscape including the vegetation. Remnant forests can be protected, and degraded riverine boundaries replanted as conservation lands. In circumstances where no forest stands exist reforestation can assist in offsetting these impacts or the landscape converted to parklands, which need to be valued by the city’s residents. The upper Matanikau and Lungga areas can possibly be converted to protected areas. There should not be any extractive industry above these watershed areas.
3. Considering a more wider watershed perspective can also encourage changes in the way solutions are reached that simultaneously satisfies certain regulatory requirements. For example, if the entire upper Lungga and Matanikau to Kongulai watershed were protected, that would easily satisfy the Protected Areas Act 2010 and Environment Act 1998. Also satisfying some the acts specific objectives like improving access to clean water, promote the protection of ecosystems natural habitats, or promote environmentally sound and sustainable development in areas adjacent to protected areas. Watershed planning can also empower us to make sounder choices about how we develop, maintain, and construct, drainage systems, control riverine development, and particularly ceasing the aesthetic (plastic dumping), and sewage pollution of Matanikau River that can easily satisfy the River Water Act 1964 and the Environmental health Act 1980.
As urban sprawl continues to increase in and around Honiara, water flows will also increase throughout developed areas. When natural vegetation is further replaced with impervious surfaces (roads, buildings etc) runoff from rain will increase flushing sediment and pollutants into streams. This was very obvious during the previous and recent heavy rain. This impacts on surface water quality, which is very obvious along the Matanikau River.
We would like to suggest the relevant government authorities in collaboration with relevant institutions work on a watershed management program that focuses on recovering stream habitats, surface water restoration, and improving healthy streams and rivers and improving the understanding of ecological systems that foster this dynamic balance within the upper Honiara watershed catchments. Also to increase the awareness to all the people who occupy this river boundary from polluting the river ways with all forms of waste, plastic or non-biodegradable materials.