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 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 Low flow spells increase in severity and duration Low flow spells increase in severity and duration Low flow spells increase in severity and duration Increased TMDs drive additional declines in total available flow volume in typical years, affecting base flows. 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. D 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 Warmer climate future slightly increases peak flow magnitudes and variability, likely due to earlier melt and increased probability of rain-on-snow events Increased TMD diversions during high flow season further reduce the return frequency of high peak flows. Upstream reservoir fills diminish peak flood flow magnitudes and frequencies
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 Increased TMD diversions further reduce peak flow magnitudes, durations, or frequency in dry years. Upstream reservoir fills diminish peak flood flow magnitudes and frequencies
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. B 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 Increased TMD diversions further reduce peak flow magnitudes, durations, or frequency in typical years. Upstream reservoir fills diminish peak flood flow magnitudes and frequencies
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. C 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 Increased TMD diversions further reduce total annual flow volume in dry years.
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. B 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 Increased TMD diversions further reduce total annual flow volume in typical years. 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. A 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 Further decreases to peak flows and total volumes decrease sediment transport capacity and loads from current levels. Changes in streamflow regimes including declines in peak flows and total volumes due to reservoir operations further alters sediment transport regimes 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. F Changes in flow regimes maintain or increase frequency of discharges at or above sediment mobilization thresholds Changes in flow regimes drive decreased frequency of discharges at or above sediment mobilization thresholds Increased TMDs diversion volumes further reduce peak flows (geomorphic flows) and total annual flow, decreasing the frequency and duration of flushing flows. Changes in flow regimes drive decreased 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
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. C
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. C Increasing air temperatures and decreasing summer/fall baseflows creates increasing temperature risks for aquatic life Increasing air temperatures and decreasing summer/fall baseflows creates increasing temperature risks for aquatic life Increasing air temperatures and decreasing summer/fall baseflows creates increasing temperature risks for aquatic life Reservoir management frameworks that include summer/fall baseflow augmentation may somewhat offset temperature risks from warming air and lower late seasons flows
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. B
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. B Continued development further alters, degrades, removes, or fragments riparian forest buffers Increased frequency and/or duration of seasonal drying and hot spells exposes riparian forests to greater catastrophic fire risk
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. B
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. A
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. B 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 Increased TMD diversions decrease total annual flow volumes, potentially decreasing in-channel connectivity during low flows. Reservoir augmentation of late summer baseflows may somewhat mitigate climate-induced reductions.
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. Continued increases to impervious area, increased stormwater volumes, and riparian losses/degradation impact community balance and sensitive species 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. Reservoir augmentation of late summer and early fall baseflows helps maintain habitat refugia and cooler water temperature 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 Increased municipal diversions places increasing pressure on instream flows, water quality (temperature, DO, nutrients, etc.), habitat connectivity Riparian impacts and increased stormwater pollutant fluxes are likely to degrade physical and chemical fishery habitat 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