Changes in the frequency and duration of closures of the opihi hapua following construction of the Opuha Dam

Abstract

Hapua are coastal lagoons found at the mouths of braided gravel rivers that experiee a semi-permanent connection with the ocean related to fluvial discharge and marine sediment deposition. Sustained closure is driven by low river flows and is associated with a decrease in water quality, the impedance of fish passage and flooding. On many Hapua, irrigation schemes have modified natural flow regimes, yet there is little field data on how this affects the dynamics of the lagoon. In this study we examine the Opihi rivermouth (New Zealand) which has a naturally seasonal low flow regime and a hydrology extensively modified through irrigation abstraction and dam construction Analysis of the entranc..