Functional Assessment
Potential Future Drivers
Variable / Sub-Variable Existing Condition Increasing Municipal Water Use Urbanization Warm & Wet Climate Future In-Between Climate Future Hot and Dry Climate Future New TMDs Increased Reservoir Capacity Wildfire
Streamflows
Base Flow: Dry YearBaseflows are the lowest flows of the year. In the Eagle River's snowmelt-controlled hydrologic cycle, they often occur during late summer and through the heart of winter, fed by groundwater and minimal surface runoff. These flows determine the minimum area of inundated habitat available for aquatic life. Lower flows are less able to buffer warm summer air temperatures and dilute human-sourced pollutants. B Increasing municipal deman may paradoxically increase augmentation requirements during winter low flows Onset and peak snowmelt shift earlier in season, exacerbating severity and duration of late season low flow spells Onset and peak snowmelt shift earlier in season, coupled with increasing air temperatures, exacerbating severity and duration of late season low flow spells Onset and peak snowmelt shift earlier in season, coupled with increasing air temperatures, exacerbating severity and duration of late season low flow spells Reservoir augmentation of late summer baseflows may somewhat mitigate climate-induced reductions.
Base Flow: Median YearBaseflows are the lowest flows of the year. In the Eagle River's snowmelt-controlled hydrologic cycle, they often occur during late summer and through the heart of winter, fed by groundwater and minimal surface runoff. These flows determine the minimum area of inundated habitat available for aquatic life. Lower flows are less able to buffer warm summer air temperatures and dilute human-sourced pollutants. A Increasing municipal deman may paradoxically increase augmentation requirements during winter low flows Low flow spells increase in severity and duration Low flow spells increase in severity and duration Low flow spells increase in severity and duration Reservoir augmentation of late summer baseflows may somewhat mitigate climate-induced reductions.
High Peakflow FrequencyThe annual return frequency of very high flow events (spring snowmelt peak flows) has important implications for channel and floodplain physical structure, constantly building and reworking the template on which in-channel and riparian communities can grow and thrive. A Wetter and warmer climate future slightly increases peak flow magnitudes and variability Warmer climate future slightly increases peak flow magnitudes and variability, likely due to earlier melt and increased probability of rain-on-snow events Streamflow losses to warming temperatures outpace potential precipitation gaines, reducing magnitude and frequency of flood flows
Peak Flow: Dry YearPeak flows sculpt overall channel and floodplain shapes and structure, reworking large sediments, scouring pools, opening up new riparian area for colonization, and transporting watershed sediment downstream. Reduction in the size and frequency of peak flows can cause profound shifts in the physical shape of channels as wells instream and riparian habitats. C Wetter and warmer climate future slightly increases peak flow magnitudes and variability; increased peak flows may be accompaied by shorter duration of high flows. Warmer climate future slightly increases peak flow magnitudes and variability; increased peak flows may be accompaied by shorter duration of high flows. Streamflow losses from warming climate result in declines in magnitude and frequency of peak flows
Peak Flow: Median YearPeak flows sculpt overall channel and floodplain shapes and structure, reworking large sediments, scouring pools, opening up new riparian area for colonization, and transporting watershed sediment downstream. Reduction in the size and frequency of peak flows can cause profound shifts in the physical shape of channels as wells instream and riparian habitats. A Wetter and warmer climate future slightly increases peak flow magnitudes and variability Streamflow losses from warming climate result in declines in magnitude and frequency of peak flows
Total Volume: Dry YearTotal flow volume describes the annual amount of water flowing past a location. Changes (usually reductions) in annual volume are a high-level indicator that consumptive needs and hydrologic alteration (diversions or storage) may be impacting a stream reach. Losses in flow have to occur somewhere in the annual hydrologic regime, and different timings have differing impacts. For example, significant reductions in peak flows may alter channel-forming and sediment transport processes, while reductions in late summer base flows have signifcant implications for water quality, pollutant dilution, water temperature, and habitat availability. B Total streamflow declines due to warming temperatures (increased vegetation ET demand, lower soil moisture, longer growing/irrigation season) outpace potential gains from precipitation increases, causing overall streamflow declines Total streamflow declines due to warming temperatures (increased vegetation ET demand, lower soil moisture, longer growing/irrigation season) drive overall streamflow declines Total streamflow declines due to warming temperatures (increased vegetation ET demand, lower soil moisture, longer growing/irrigation season) drive overall streamflow declines
Total Volume: Median YearTotal flow volume describes the annual amount of water flowing past a location. Changes (usually reductions) in annual volume are a high-level indicator that consumptive needs and hydrologic alteration (diversions or storage) may be impacting a stream reach. Losses in flow have to occur somewhere in the annual hydrologic regime, and different timings have differing impacts. For example, significant reductions in peak flows may alter channel-forming and sediment transport processes, while reductions in late summer base flows have signifcant implications for water quality, pollutant dilution, water temperature, and habitat availability. A Total streamflow declines at higher watershed stream reaches due to warming temperatures (increased vegetation ET demand, lower soil moisture, longer growing/irrigation season) are balanced or slightly exceeded by gains from precipitation increases Total streamflow declines due to warming temperatures (increased vegetation ET demand, lower soil moisture, longer growing/irrigation season) drive overall streamflow declines
Streambed Sediment
Continuity and TransportHealthy rivers in balance can transport their sediment loads successfully over time, without unnatural interruptions or rates of deposition/erosion that result in habitat degradation, unnatural channel movements and forms, and negative infrastructure impacts. B Increased flashiness, physical channel impacts (bank cover, resistance, hydraulic geometries) alter sediment supply and transport regimes Increased peak flows or frequency of effective discharges maintains channel's self-maintenance capabilities Decreased total volumes and base flow magnitudes salter total annual sediment transport capacity Increased watershed responsiveness can drive increased peak floods and sediment delivery, impacting channel shaping processes like erosion/aggradation rates and seasonal sediment transport
Flushing FlowsFlushing flows are the relatively frequent higher spring flows that clean out gravels and cobbles, moving fine sediment away and ensuring health habitat for bug life and fish spawning. A Changes in flow regimes maintain or increase frequency of discharges at or above sediment mobilization thresholds Changes in flow regimes maintain or increase frequency of discharges at or above sediment mobilization thresholds
Water Quality
MetalsElevated levels of dissolved metals occur frequently from legacy mining impacts in Colorado, but also more-recently from stormwater runoff tied to urbanized land areas and and transportation infrastructure. Metals impact aquatic insect communities that form the food web base and impact fish health, including successful juvenile development. A Runoff from burned areas increases dissolved metals loads to streams
NutrientsNutrients include chemicals like nitrogen and phosphoruous from human and agricultural wastes as well as stormwater runoff. Mountain streams and the aquatic life adapted to liver here are typically nutrient-poor; elevated levels can serve as pollutants that alter macroinvertebrate community sttucture, drive excessive growth of streambed-choking algae, and lead to low dissolved oxygen events and other water quality imapcts. A Runoff from burned areas increases nutrient loads to streams
TemperatureWater temperature, along with streamflow, is a key control on instream aquatic habitat. Most species in the Eagle Basin are adapted to cold mountain rivers. Warming water temperatures due to climate change, land use conversion, and removal of mature riparian forests pose significant problems for these instream wildlife communities. A
Riparian Areas
Floodplain physical conditionFloodplains support healthy rivers by allowing high flows to overtop banks and spread out onto the landscape, and supporting diverse riparian wetlands and forests that protect instream water quality and support numeroud species. In the process, enriching riparian wetlands and forests, recharging local aquifers, and dissipating potentially damaging flood energy. Floodplains that have been altered and fragmented by agriculture use, roads, berms, dikes, and forest clearing have a diminished ability to perform these functions. C
Riparian vegetationRiparian vegetation forms a protective buffer along river corridors, attenuating polluted runoff and natural stabilizing stream banks and river shape. In addition, they support vibrant wildlife communities and safe long-term movement corridors. C
River Form
Channel Structure and DynamicsChannel structure is the physical form of the river channel, and channel dynamics include the constantly ongoing processes of sediment transport, erosion, deposition, and movement that control these forms. Rivers in equilibrium with their flow regime, with a naturalized supply of sediment and unaltered banks and floodplains tend to assume relatively stable forms on the landscape over time. Heavily altered channel dynamics may result in channel instability and negative repurcussions for streamhealth, adjacent riparian habitats and human communities and infrastructure. C Increased sediment fluxes impact channel shaping processes including aggradation rates and seasonal sediment transport
Aquatic Habitat
Habitat StructureHabitat structure describes the set of instream features variously occuring throughout a stream system. Features include pools, riffles, gravel bars, boulder eddies, undercut banks, large woody debris, and many others. A diversity of habitats supports stream health by providing ecological niches for many different aquatic life species, as well as the multiple life stages and needs of individual species. B Increased sediment fluxes degrade inchannel habitat quality including spawning sites and macroinvertebrate habitat
In-channel Hydrologic ConnectivityBarriers to stream network connectivity such as dams, culverts, diversion structures, or seasonally de-watered stream segments may interfere with or completely stop the ability of fish and other species to make critical movements and annual migrations for feeding, spawning, and seeking refuge during periods of flow or temperature stress. A Baseflow declines reduce stream network connectivity during late summer and fall, potential impacts to refuge seeking movements, migration, and spawning activity Baseflow declines reduce stream network connectivity during late summer and fall, potential impacts to refuge seeking movements, migration, and spawning activity Baseflow declines reduce stream network connectivity during late summer and fall, potential impacts to refuge seeking movements, migration, and spawning activity Baseflow declines reduce stream network connectivity during late summer and fall, potential impacts to refuge seeking movements, migration, and spawning activity
Aquatic Life
Aquatic InsectsBug life serves as a key indicator of stream health and water quality, underpinning the food webs for other prized aquatic life like trout. These 'canaries in the coal mine' are often the first signal that ecosystems are experiencing pollution or stress. D Low flow spells severity and duration still increase in summer/fall still under WW future, negatively impacting abundance. Low flow spells severity and duration still increase in summer/fall still under WW future, negatively impacting abundance. Low flow spells severity and duration greatly increase in summer/fall HD future, negatively impacting abundance. Streambed Sedimentation and water chemistry impacts degrade physical habitat and water quality
FishFish community structure (species types, age classes, functional guilds) should be native and appropriate to the stream channel type, natural water quality conditions, and landscape location. Fish communities that are absent or out of balance may indicate disturbed ecosystems or ongoing impacts to habitat, water quality, or physical processes such as flow regimes and sediment transport. A Declining late summer/early fall flows place increasing pressure on instream flows, water quality (temperature, DO, nutrients, etc.), habitat connectivity Declining late summer/early fall flows and increasing air temperatures place increasing pressure on instream flows, water quality (temperature, DO, nutrients, etc.), habitat connectivity Declining late summer/early fall flows and increasing air temperatures place increasing pressure on instream flows, water quality (temperature, DO, nutrients, etc.), habitat connectivity Increased sediment fluxes degrade inchannel habitat quality and water quality, including spawning sites and macroinvertebrate habitat