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| EFC type | Hydrologic parameters | Ecosystem influences |
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| (1) Monthly low flows | Mean or median values of low flows during each calendar month
(Subtotal 12 parameters) | (1) Provide adequate habitat for aquatic organisms; (2) maintain suitable water temperatures, dissolved oxygen, and water chemistry; (3) maintain water table levels in floodplain, soil moisture for plants; (4) provide drinking water for terrestrial animals; (5) keep fish and amphibian eggs suspended; (6) enable fish to move to feeding and spawning areas; (7) support hyporheic organisms (living in saturated sediments) |
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| (2) Extreme low flows | Frequency of extreme low flows during each water year or season
Mean or median values of extreme low flow event
Duration (days)
Peak flow (minimum flow during event)
Timing (Julian date of peak flow)
(Subtotal 4 parameters) | (1) Enable recruitment of certain floodplain plant species; (2) purge invasive and introduced species from aquatic and riparian communities; (3) concentrate prey into limited areas to benefit predators |
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| (3) High flow pulses | Frequency of high flow pulses during each water year or season
Mean or median values of high flow pulse event
Duration (days)
Peak flow (maximum flow during event)
Timing (Julian date of peak flow)
Rise and fall rates
(Subtotal 6 parameters) | (1) shape physical character of river channel, including pools, riffles; (2) determine size of streambed substrates (sand, gravel, cobble); (3) prevent riparian vegetation from encroaching into channel; (4) restore normal water quality conditions after prolonged low flows, flushing away waste products and pollutants; (5) aerated eggs in spawning gravels and prevent siltation; (6) maintain suitable salinity conditions in estuaries |
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| (4) Small floods | Frequency of small flood during each water year or season
Mean or median values of high flow pulse event
Duration (days)
Peak flow (maximum flow during event)
Timing (Julian date of peak flow)
Rise and fall rates
(Subtotal 6 parameters) | Applies to small and large floods:
(1) provide migration and spawning cues for fish; (2) trigger new phase in life cycle (i.e., insects); (3) enable fish to spawn in floodplain and provide nursery area for juvenile fish; (4) provide new feeding opportunities for fish, water flow; (5) recharge floodplain water table; (6) maintain diversity in floodplain forest types through prolonged inundation (i.e., different plant species have different tolerances); (7) control distribution and abundance of plants on floodplain; (8) deposit nutrients on floodplain |
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| (5) Large flood | Frequency of large flood during each water year or season
Mean or median values of high flow pulse event
Duration (days)
Peak flow (maximum flow during event)
Timing (Julian date of peak flow)
Rise and fall rates
(Subtotal 6 parameters) | Applies to small and large floods:
(1) maintain balance of species in aquatic and riparian communities; (2) create sites for recruitment of colonizing plants; (3) shape physical habitats of floodplain; (4) deposit gravel and cobbles in spawning areas; (5) flush organic materials (food) and woody debris (habitat structures) into channel; (6) purge invasive, introduced species from aquatic and riparian communities; (7) disburse seeds and fruits of riparian plants; (8) drive lateral movement of river channel, forming new habitats (secondary channels, oxbow lakes); (9) provide plant seedlings with prolonged access to soil moisture |
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