Using water destined for irrigation to conserve wetland ecosystems: A basis for assessing feasibility



[1] Regulated rivers often have associated wetlands with declining ecological health due to reduced inundation frequency. One innovative option to improve the ecological condition of such wetlands is to use them as temporary off-river water storages, where the water used to inundate them is subsequently allocated to consumptive use. The hydrologic feasibility of this option has yet to be demonstrated. We investigated three physical aspects of a floodplain wetlands system that must be considered, relative to irrigation demand, to determine feasibility: (a) historical inundation frequencies and the effect of regulation and climate change, (b) natural storage volumes and enhanced volumes using retaining walls, and (c) estimated loss rates. We found that inundation frequencies are reduced under regulation and that this reduction is even greater for projected climate change scenarios. Natural volumes were found to be 5% of annual irrigation demand, increasing to 20% with retaining walls; a small proportion at the system scale but significant at farm scale, especially with opportunities for multiple fillings per season. Losses are estimated at 36%–63% of the initial volume, depending on timing of wetland inundation and drawdown. Careful consideration must be applied to issues of frequency and timing of inundation, drawdown rates, and connectivity when considering the ecological benefits of using wetlands as storages. Environmental benefits will be a trade-off with capital, operational, and maintenance costs and water pricing.