Marrakech
Conference
Information
Hub
KEY STEPS
NEGOTIATIONS
FOCUS
PROCESS
|
|
Your location: Home |
|
Compendium on methods and tools to evaluate impacts of, and vulnerability and adaptation to, climate
change
|
Bruun Rule Description
|
|
Description
|
The first and best known model relating shoreline retreat to an increase in local sea level is that
proposed by Per Bruun (1962). The IPCC reports that 1 cm rise in sea level erodes beaches about 1 m
horizontally. This becomes a large issue for developed beaches that are less than 5 m from the ocean
(IPCC, 1998).
The Bruun rule states that a typical concave-upward beach profile erodes sand from the beach face and
deposits it offshore to maintain constant water depth. The Bruun rule can be applied to correlate
sea-level rise with eroding beaches. The Bruun rule estimates the response of the shoreline profile
to sea-level rise. This simple model states that the beach profile is a parabolic function whose
parameters are entirely determined by the mean water level and the sand grain size. The analysis by
Bruun assumes that with a rise in sea level, the equilibrium profile of the beach and shallow
offshore moves upward and landward.
The analysis is two-dimensional and assumes that,
- The upper beach is eroded due to the landward translation of the profile;
- The material eroded from the upper beach is transported immediately into the offshore and
deposited, such that the volume eroded is equal to the volume deposited;
- The rise in the nearshore bottom as a result of deposition is equal to the rise in sea level,
thus maintaining a constant water depth in the offshore (SCOR, 1991).
|
|
Appropriate Use
|
The Bruun rule is only applicable for small scale local sites.
|
|
Scope
|
Over long stretches of coast, the Bruun rule and associated cross-shore transport models become
complex. There has been a number of critiques e.g. Cooper and Pilkey (2004).
|
|
Key Output
|
Shoreline recession (in metres relative to sea-level rise).
|
|
Key Input
|
An increase in sea level, (S), cross shore distance (L) to the water depth (h) taken by Bruun as the
depth to which nearshore sediments exist (depth of closure), and B is the height of the dune.
|
|
Ease of Use
|
Easy to use with numerous assumptions.
|
|
Training Required
|
Familiarity with the coastal zone being investigated.
|
|
Training Available
|
None
|
|
Computer Requirements
|
None, unless it is incorporated into a model.
|
|
Documentation
|
Originally proposed by Per Bruun in 1962.
|
International Studies
|
Bruun (1962, 1988)
|
|
Contacts for Framework, Documentation, Technical Assistance
|
See applications
|
|
Cost
|
No cost to use the Bruun rule.
|
Validity
|
Bruun rule has been applied but caution needs to be exercised where other factors influence sediment
budget or control profile.
|
|
|
| |
|
