How are environmental flow requirements determined for rivers?

Environmental flows maintain river ecosystem health. Assessment methods: (1) Hydrological - percentage of natural flow (Tennant method), flow duration analysis, (2) Hydraulic - maintain habitat (wetted perimeter, depth criteria), (3) Habitat simulation - PHABSIM links flow to habitat suitability indices for target species, (4) Holistic - expert panels considering all ecosystem components (DRIFT, ELOHA). Key flow components: low flows for water quality, high flows for channel maintenance and floodplain connection, seasonal variation for life cycles. E-flows compete with consumptive uses, requiring integrated water management.