Table 1. Summary of the five environmental flow components (EFCs) used in the Indicators of Hydrologic Alteration software, and their ecosystem influences.       EFC type Hydrologic parameters   Ecosystem influences 1. Monthly low flows Mean or median values of low flows during each calendar month   Provide adequate habitat for aquatic organisms   Maintain suitable water temperatures, dissolved oxygen, and water chemistry   Maintain water table levels in floodplain, soil moisture for plants   Provide drinking water for terrestrial animals   Keep fish and amphibian eggs suspended   Enable fish to move to feeding and spawning areas   Support hyporheic organisms living in saturated sediments   Subtotal 12 parameters         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 (d)   Magnitude (minimum flow during event)   Timing (Julian date of peak flow)     Enable recruitment of certain floodplain plant species   Purge invasive, introduced species from aquatic and riparian communities   Concentrate prey into limited areas to benefit predators Subtotal 4 parameters         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 (d)   Peak flow (maximum flow during event)   Timing (Julian date of peak flow)   Rise and fall rates   Shape physical character of river channel, including pools, riffles   Determine size of streambed substrates, e.g., sand, gravel, cobble   Prevent riparian vegetation from encroaching into channel   Restore normal water quality conditions after prolonged low flows, flushing away waste products, and pollutants   Aerate eggs in spawning gravels, prevent siltation   Maintain suitable salinity conditions in estuaries   Subtotal 6 parameters         4. Small floods, i.e., 2-10 yr events Frequency of small floods   Mean or median values of small flood event:   Duration (d)   Peak flow (maximum flow during event)   Timing (Julian date of peak flow)   Rise and fall rates   May apply to small or large floods:   Provide migration and spawning cues for fish   Trigger new phase in life cycle, i.e., insects   Enable fish to spawn in floodplain, provide nursery area for juvenile fish   Provide new feeding opportunities for fish, waterfowl   Recharge floodplain water table   Maintain diversity in floodplain forest types through prolonged inundation, i.e., different plant species have different tolerances   Control distribution and abundance of plants on floodplain   Deposit nutrients on floodplain   Subtotal 6 parameters         5. Large floods, i.e., >10-yr events Frequency of large floods   Mean or median values of large flood event:   Duration (d)   Peak flow (maximum flow during event)   Timing (Julian date of peak flow)   Rise and fall rates   May apply to small or large floods:   Maintain balance of species in aquatic and riparian communities   Create sites for recruitment of colonizing plants   Shape physical habitats of floodplain   Deposit gravel and cobbles in spawning areas   Flush organic materials such as food and woody debris such as habitat structures into channel   Purge invasive, introduced species from aquatic and riparian communities   Disburse seeds and fruits of riparian plants   Drive lateral movement of river channel, forming new habitats, e.g., secondary channels, oxbow lakes   Provide plant seedlings with prolonged access to soil moisture   Subtotal 6 parameters   Grand total 34 parameters