2. Evolution of “Restoration”
Long history of working on and manipulating
streams and rivers
“Restoration”, “Rehabilitation”, “Stabilization” have
all been used as justification to undertake restoration
We continue to learn about, and evolve the science
3. 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
4. The Order of Restoration
In any stream restoration there is an order that
should be followed.
• Protect
• Maintain
• Restore
• Enhance
Consider passive vs. active restoration, such as
valley wide protection, floodplain restoration before
more intensive efforts such as channel restoration
and habitat enhancement structures.
5. 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.
6. Restoration Objectives
•Must meet socio-economic,
ecological, physical,
engineering, and regulatory
goals of the project.
• Result should be stable,
not static.
• Be appropriate for the
physical setting (climate,
land use, development
restrictions, geology)
7. Restoration Tools & Approaches
Approach – form based
versus process based
Awareness of viability
What approach should you
use?
Need for
understanding
processes operating
within your system
9. 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
10. Channel Stability
• Essentially a balance
between flow regime
and sediment loads
• While stable, the
channel may adjust its
form, profile and position
on its floodplain
•When stable, the channel can accommodate
changes in flow or sediment, as long as a threshold
is not exceeded without altering its form.
11. 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.
12. “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
13. Restoration –Considerations
Scale of the site (bank
treatment versus channel
realignment)
Design Process
Data collection
Analyses
Design iterations
Integration of
disciplines/design
components
Implementation
14. 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
15. Data Collection
• Reach and cross-
section scale
• Used to determine &
quantify channel
processes
• Necessary for all
design approaches
17. Hydrology
Flow 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)
18. 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.
19. Hydraulic Analysis
Used to determine the impacts of flow on the
channel, (how much and how fast), and other
relations essential to restoration designs.
Flow modeling
• a simulation that represents the channel through geometry
Sediment 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
20. Design Discharge
How 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
23. Options to move or enhance the stream
Existing Section
Restoration Section
24. Construction Implementation
Erosion & Sediment Control
•How we keep the process
from impacting the valley
Constructability
•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 the
channel dealt with
