Evolution of “Restoration”Long history of working on and manipulating streams and rivers“Restoration”, “Rehabilitation”, “Stabilization” have all been used as justification to undertake restorationWe continue to learn about, and evolve the science
So, what is “restoration”? To return to a healthy state To recover function As a stream environment changes, so do the expectations Each project is unique
The Order of RestorationIn any stream restoration there is an order thatshould be followed. • Protect • Maintain • Restore • EnhanceConsider passive vs. active restoration, such asvalley wide protection, floodplain restoration beforemore intensive efforts such as channel restorationand habitat enhancement structures.
A Restoration Philosophy• Rivers, like most other natural systems, are highly dynamic and complex. The numerous processes and interactions that continually occur at varying scales are testaments to this natural complexity.• This complexity provides and sustains the various niches and habitats for biological organisms.• Recent advances in both physical and biological sciences, in addition to our growing understanding of these systems, has contributed to our ability to restore the natural dynamics and functions of rivers.
Restoration Objectives•Must meet socio-economic,ecological, physical,engineering, and regulatorygoals of the project.• Result should be stable,not static.• Be appropriate for thephysical setting (climate,land use, developmentrestrictions, geology)
Restoration Tools & ApproachesApproach – form basedversus process basedAwareness of viabilityWhat approach should youuse? Need for understanding processes operating within your system
Channel Evolution As a channel deepens, it reaches a limit, a hard layer that is harder to erode. If it cant move downward, it will move to the side When if moves to the side, banks will erode and the channel becomes wider The channel will then re- establish itself
Channel Stability• Essentially a balancebetween flow regimeand sediment loads• While stable, thechannel may adjust itsform, profile and positionon its floodplain•When stable, the channel can accommodatechanges in flow or sediment, as long as a thresholdis not exceeded without altering its form.
When a channel becomes unstable• Depending upon nature and magnitude of the disturbance, a threshold in the stream may be exceeded, which will lead to substantial change and adjustment.• A channel will strive to achieve equilibrium but this can take decades to occur.
“Natural Channel Design”- Emphasizes geometry, plan, profile that will be stable under given flow/sediment regime with minimal armor/maintenanc e- Assumes most functions follow from geomorphic condition
Restoration –ConsiderationsScale of the site (bank treatment versus channel realignment)Design Process Data collection Analyses Design iterations Integration of disciplines/design componentsImplementation
Bank Erosion• Bank material more variable than bed material• Many factors involved in analysis – Flow properties – Bank composition – Climate – Subsurface conditions – Channel geometry – Mode of failure – Biology – Vegetation
Data Collection• Reach and cross-section scale• Used to determine &quantify channel processes• Necessary for alldesign approaches
Design Analyses• Hydrology• Sediment transport• Geomorphicrelations• System dynamics
HydrologyFlow Duration Curves The flow duration curve is a plot that shows the percentage of time that flow in a stream is likely to equal or exceed some specified value of interest.Flow Frequency The probability a given streamflow will be exceeded in any given year. Related to Return-Interval (e.g. 100-Year Flood)
Why do we care about Hydrology?Properly developed statistical hydrology Allows for quantification of risk and success/failure Allows for the development of specific design criteria Provides tool for estimating bankfull discharges Critical link to understanding how physical conditions such as bank and bed shear stress and other sediment transport functions vary temporally.
Hydraulic AnalysisUsed to determine the impacts of flow on thechannel, (how much and how fast), and otherrelations essential to restoration designs.Flow modeling • a simulation that represents the channel through geometrySediment transport modeling •To understand the amount of sediment moving through the system •Can help to determine long term stability of the channel •Can be used to estimate sediment yield, and for comparative analysis between reaches
Design DischargeHow do we select which flow to design for? • Low flow ~ habitat design • Bankfull Discharge ~ stable channel design • Flood Flows ~ regulatory compliance and flood hazard protection
Examples of Natural Design Typical dynamic meander pattern
Options to move or enhance the stream Existing Section Restoration Section
Construction ImplementationErosion & Sediment Control•How we keep the processfrom impacting the valleyConstructability•How can it be constructed?Details on how to build it•Where to access the work•What are the soils like•How are the flows in thechannel dealt with
Access Considerations•Protect the channel•Minimize disturbance•Optimize materials delivery