The Hydrological Viability of Te Harakiki Wetland, Waikanae
Wetlands are unique natural resources that play an important role in the hydrological cycle. There is a dynamic link between wetland hydrology and inputs from both surface and groundwater resources. Shallow groundwater abstraction near the Te Harakiki wetland at Waikanae has the potential to impact on the wetland' hydrosystem. To assess the likelihood of this occurring, a detailed analysis of recent changes, the hydrological regime, and the water balance of the Te Harakiki Wetland system was undertaken. The hydrological regime of the wetland system was assessed by various monitoring sites established around Te Harakiki to measure rainfall, soil moisture, surface and groundwater levels. Analysis of (decadal) historical aerial photographs allowed changes in spatial extent of the open water habitat (lagoon) and the urban area of Waikanae Beach. Comparisons were made between wetland extent, population increase and urban area expansion. These data, together with a simple water balance, and historical climatic records, were used to explain the drastic decrease in wetland extent. Climatic factors and goundwater are the major driving forces behind the wetland's hydrologic regime. The surface water outflow from the system is greater than the surface water inflow, but this may be affected by the tides. The surface and groundwater systems in the area are closely linked. They have similar responses to rainfall events. Groundwater abstraction in the area appears to have minimal impact on the water level within the wetland. The exact nature and extent of abstraction around the wetland is unknown. The reduction in flood pulsing as a result of channel modification, and the fragmentation of the area for the construction of the oxidation ponds are the likely explanation. The current restoration efforts in regard to controlling pest species and excluding stock from the wetland have halted the decline in wetland area. The future of the Te Harakiki wetland system is now more positive.