Investigating Tradeoffs between Agricultural Development and Environmental Flows under Climate Change in the Stung Chinit Watershed, Cambodia

The interlinkages between water for irrigation and for fish habitat are complex. This is particularly true in the Stung Chinit, a tributary to one of the most robust fisheries in the world, where livelihoods rely heavily on rice production and fishing and there is pressure to increase rice production with increased irrigation. This study assesses the tradeoffs between various management options and irrigation strategies in the Stung Chinit watershed under multiple projections of climate change. Due to the relative demands for instream flows and rice, if dry season rice is widely promoted, flows will be severely impacted. However, implementing a flow requirement protects these flows, while only causing minor shortages to rice when planted once or twice per year. These shortages may be alleviated with improved cooperation, management and shifting rice irrigation practices. While climate change will lead to warming temperatures and potentially higher demands for irrigation, the larger threat to rice and ecosystems appears to be water management (or lack thereof). This study suggests that there is sufficient water in the system to expand the irrigated area by 10%, grow rice twice per year and protect downstream flows under climate change; however, well-coordinated management is required to achieve this.

Beyond Adjudication

As adjudication extends into a new century, water managers must address new demands, including the water needs of endangered species and rivers themselves. Climate changes also put the utility of adjudication’s detailed measurements and allocations into question. Under a changing climate, the Southwest is expected to be warmer and drier. This chapter argues, however, that New Mexico has to account for future instream flows and existing climate change alterations of river flow regimes. The office of the state engineer will have to balance the new quantity demands of the Anthropocene and the warming climate with the already-difficult human demands by particular groups who want water quality to be a central focus in the future.

Use of Instream Structure Technique for Aquatic Habitat Formation in Ecological Stream Restoration

Drought flow as the minimum flow rate required for restoration of the Mokgamcheon stream was calculated by the Storm Water Management Model (SWMM) V.5.0. The adequacy of drought flow to guarantee the minimum ecological environment was assessed using suitable low-flows not exceeding the maximum pollution concentration of the ecosystem calculated by Design FLOWs (DFLOW) V.4.1. Fish flows, which provide proper ecological habitat for fish, were calculated using Physical HABitat SIMulation (PHABSIM) V.1.5.2 to provide proper ecological habitat for target fishes such as Carassius auratus and Zacco platypus. The monthly expected instream flows were determined as the largest value between drought flow and fish flow. In most cases, instream flows were determined by drought flows exceeding fish flows that satisfy the condition of species habitat, but in the case of Carassius auratus, drought flows were less than fish flows in April, September, and October. Thus, structural measures for the supply of additional discharge were required. Instead, when natural environment-friendly instream structures, such as stepping stones were used, affordable ecological restoration that met the preferred conditions for discharge and depth of Carassius auratus was possible. The stepping stones were assessed using River2D V.0.95a to measure their effectiveness compared to other structural measures that would be costly and time-consuming to secure shortage of fish flow. Finally, the stability of the habitat was assessed through flood analysis; in case of a flood discharge of 5.2 m3/s obtained from time-series analysis, it was evaluated that the stability of habitats could be reasonable.