Lecture19 "Natural Flow Regime" Reading Summary

“The **Natural Flow Regime” Summary

Many rivers no longer support socially valued native species or sustain healthy ecosystems that provide important good and services (think salmon, non-toxic water…)
Consequences of current (poor) river management:
-Extirpation of species
-closures of fisheries
-declines in water quality
-groundwater depletion
-more frequent/intense flooding

Stream Flow = “master variable” that limits distribution and abundance of riverine species
Environmental dynamism is now recognized as central to sustaining and conserving native species diversity and ecological integrity

-The Natural Flow Regime (characteristic pattern of a river’s flow, quantity, timing and variability)
The frequency of large floods can be estimated by paleohydrologic studies (wood debris)
Five critical components of flow:
1)Magnitude=amount of water moving past fixed point
2)Frequency=how often a flow above a given magnitude recurs over given time period
3)Duration=period of time associated with a specific flow
5)Rate of Change/Flashiness=how quick flow changes

-Hydrologic Processes and the Flow Regime
Precipitation becomes surface, soil and ground water
Water pathway determined by combination of climate, geology, topography, soils and vegetation
Local and regional flow patterns determined by variability of precipitation, terrain, soil and ET

-The Natural Flow Regime Organizes and Defines River Ecosystems
…notably through movement of water and sediments within channel
Predictable diversity from flow pattern (spatial and temporal)

-Human Alteration of Flow Regimes
…results in gross and fine scale changes in habitat
Example: Dams, Land-Use Activities (timber harvesting, livestock grazing, agriculture, urbanization)
Large amount of science used to establish a fair analysis of the understanding of the amount of water use that should be alloted to nature and humans

-Ecological Function of the Natural Flow Regime
Composition and abundance of species in river often reflect frequency and intensity of high flow
Timing for flows provides environmental cues for initiating life cycle transitions for fish
High flows prevent the successful establishment of non-native species

-Ecological Responses to Altered Flow Regimes
Same human activity can cause different consequences in particular areas
General species (who are more tolerant) tend to replace specialized species
Ex: SW US most native fauna is listed as Endangered
Food webs, not just single species may be altered

-Recent Approach to Streamflow Management
Instream Flow Incremental Methodology (IFIM)-established minimum allowable flow (constant)
BUT…a range of flows is necessary to scour and revitalize streams!
Need to look river system holistically, what is good for one species, may not be good for entire river system

-Managing Toward a Natural Flow Regime
*flow variability is critical to ecosystem function and native biodiversity
Need to recognize scientific limits to estimating flow regimes
Revisions of laws and regulations and redefinition of social goals and policies is essential to proper river management

Unless otherwise stated, the content of this page is licensed under Creative Commons Attribution-ShareAlike 3.0 License