Abstract
Optimal restoration and management of coastal wetland are contingent on reliable assessment of hydrological processes. In this study, we used the Soil and Water Assessment Tool (SWAT) model to assess the impacts of a proposed coastal wetland restoration plan on the water balance components of the Heeia watershed (Hawaii). There is a need to optimize between water needs for taro cultivation and accompanying cultural practices, wetland ecosystem services, and streamflow that feeds downstream coastal fishponds and reefs of the Heeia watershed. For this, we completed two land use change scenarios (conversion of an existing California grassland to a proposed taro field and mangroves to a pond in the wetland area) with several irrigation water diversion scenarios at different percent of minimum streamflow values in the reach. The irrigation water diversion scenarios aimed at achieving sustainable growth of the taro crop without compromising streamflow value, which plays a vital role in the health of a downstream fishpond and coastal environment of the watershed. Findings generally suggest that the conversion of a California grassland to a patched taro field is expected to decrease the baseflow value, which was a major source of streamflow for the study area, due to soil layer compaction, and thus decrease in groundwater recharge from the taro field. However, various taro irrigation water application and management scenarios suggested that diverting 50% of the minimum streamflow value for taro field would provide sustainable growth of taro crop without compromising streamflow value and environmental health of the coastal wetland and downstream fishponds.
Highlights
In the Hawaiian Islands, coastal wetlands represent a critical interface between terrestrial and ocean zones with a vital importance in terms of economic, cultural, and environmental values
Overall, based on the recommended quantitative statistics (NSE, RSR, and percent bias (PBIAS)), the model simulation could be judged as satisfactory because the averages of the three criteria were 0.53, 0.66, and 5.9 respectively, which are within the acceptable ranges for daily streamflow simulation [51,52]
We evaluated the impacts of the Heeia Coastal Wetland Restoration (HCWR) plan on water balance components (WBCs) at three spatial scales, which included the hydrologic response units (HRUs), sub-basins, and watershed
Summary
In the Hawaiian Islands, coastal wetlands represent a critical interface between terrestrial and ocean zones with a vital importance in terms of economic, cultural, and environmental values. Coastal wetlands are considered very attractive and agriculturally productive regions for tourists and residents. These regions play an important role against flooding, pollution, and the negative impacts of climate and land cover changes. They act like a sponge by absorbing water during the wet season and releasing it Hydrology 2020, 7, 86; doi:10.3390/hydrology7040086 www.mdpi.com/journal/hydrology. The recent financial and moral support of federal policies regarding preserving wetlands, such as “no net loss of wetlands in the United States”, has encouraged many non-profit organizations to restore the degraded wetlands [1].
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