A data-based approach to determining the optimal water ponding scale and zone for small urban wetland restoration

This study established a planning framework for effective small-scale urban wetland restoration by adapting an analytical template used for watershed-scale projects. We evaluated the optimal water ponding scale and location for small urban wetland restoration. We calculated the achievable water ponding area in Oyama Wetland, Hokkaido, Japan, by the use of an artificial water supply and elevation differences without reliance on precipitation. The volume of infiltration into the sediments, a component of the water balance equation, was estimated during a temporary suspension of the artificial water supply, and the estimate was then validated by modeling the decrease of the water ponding area from 2008, before the introduction of the artificial water supply, with high reproducibility (Nash-Sutcliffe efficiency = 0.68). The estimated attainable water ponding area was 1172 m2. We identified where a water ponding location could be most efficiently established through principal component and cluster analyses of groundwater level observation data collected from 2008 to 2010. Areas with high groundwater levels (first axis) and stable groundwater levels (second axis) accounted for approximately 73% of the cumulative contribution ratio. The calculated potentially achievable ponding area was consistent with the area achieved by the actual wetland restoration. This study shows how efficient and safe restoration of urban wetlands can be achieved with a dataset that volunteers and others can obtain independently. Long-term data analysis using the adapted template allows for clear identification of discrepancies between desired reference conditions and current conditions, facilitating the setting of objectives that promote long-term monitoring.