Comparison of discharge methods and habitat optimization for recommending instream flows to protect fish habitat

The protection of fish habitat against the impact of water extraction in rivers is a recurring problem in water resources management. As such, a wide range of methodologies is available for the calculation of instream flows. This study focuses on historical streamflow methods that rely solely on hydrometric data for instream flow evaluation. The objectives of the study are to compare different historical streamflow methods and use a jackknife resampling technique to assess the variability of instream flow estimates. Results showed that methods based on a percentage of mean annual flow (MAF) generated higher levels of instream flow protection and showed low spatial and sample size variability. Low spatial variability makes the MAF methods more suitable for calculations of instream flows for ungauged basins. The Q50 method provided relatively high levels of instream flow protection; however, spatial and sample size variability were higher than those for the MAF methods. Lastly, the results showed that some methods generated low instream flow protection (namely, the Q90, 7Q2, and 7Q10 methods), especially for small streams, and thus are not recommended for use.Key words: instream flow, aquatic habitat, water withdrawal, impact assessment.

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

Hydrology ◽

10.3390/hydrology7040095 ◽

2020 ◽

Vol 7 (4) ◽

pp. 95

Author(s):

Susan R. Bresney ◽

Laura Forni ◽

Marina R. L. Mautner ◽

Annette Huber-Lee ◽

Manish Shrestha ◽

...

Keyword(s):

Climate Change ◽

Agricultural Development ◽

Environmental Flows ◽

Fish Habitat ◽

Rice Production ◽

Management Options ◽

Instream Flows ◽

Irrigated Area ◽

The World ◽

Rice Irrigation

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.

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