Evaluation of Spatial Pattern of Altered Flow Regimes on a River Network Using a Distributed Hydrological Model

Area of Science:

• Environmental Science
• Hydrology
• River Ecology

Background:

• Temporal variability of river flow regimes is well-studied, but spatial variability remains underexplored despite its ecological significance.
• Understanding spatial flow alterations is critical for managing river ecosystems affected by human interventions.

Purpose of the Study:

• To quantify the spatial patterns of flow regime alterations along the Sagami River network in Japan.
• To estimate river discharge under both natural and altered flow conditions using a hydrological model.

Main Methods:

• Utilized a distributed hydrological model to simulate 20-year daily river discharge across the river network.
• Calculated 33 Indicators of Hydrologic Alteration (IHA) from simulated discharge to assess spatial alteration patterns.
• Validated model accuracy using correlation analysis and the Kolmogorov-Smirnov test against observed discharge data.

Main Results:

• Spatial patterns of flow regime alterations varied significantly depending on the specific hydrologic index analyzed.
• Magnitude and timing of maximum flows, monthly median flows, and frequency of low/high flow pulses were reasonably estimated.
• Strongest alterations (e.g., ~70% reduction in August median flow and high flow pulse frequency) occurred at different network locations (mainstream vs. tributary).

Conclusions:

• The distinct spatial patterns of alteration are likely influenced by the operational purposes of multiple water control facilities.
• Evaluating flow regime alterations solely at discharge gauges is inadequate for a comprehensive understanding.
• Emphasizes the necessity of assessing spatial patterns of flow regime alteration across entire river networks impacted by water management structures.