Pilarczyk K. W

International Conference on Estuaries and Coasts
November 9-11, 2003, Hangzhou, China
Fig. 1 General approach
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2. GENERAL APPROACH
2.1 TYPES AND FUNCTIONS OF COASTAL STRUCTURES
Coastal management, in its broadest sense, must take into account all factors which have
bearing on the future of the coastal zone. Politics, policy making, planning, economy and a
multitude of economic andnon-economic users (e.g. natural reserve areas), environment
protection and, by and large, sustainable development, all play significant roles and provide
both motivation and background for coastal management (Fig. 1). The factors of coastal
management may well entail many scientific and engineering disciplines other than coastal
engineering and at sites and locations far removed from the costalzone. Some of these factors
interact with one another, others are incompatible. The extent to which this applies in any
particular region, area, or specific site needs careful evaluation and compromise solutions.
This is one of the major roles of coastal management.
Fig. 2 Analysis of coastal strategies
The primary objectives of a typical coastal management study are to formulate long-termengineering planning, including financial strategies for the future usage, development and
conservation of the coastal zone. In this process, priorities should be defined both for new
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works and essential maintenance, with estimates for contingency items to cover emergency
situations, which inevitably occur (see Fig. 2). The key element in any coastal management
study is thoroughunderstanding of coastal processes by which is meant the interaction
between the hydraulic environment of winds, waves, tides, surges and currents with the
geological conditions in the coastal zone. To be effective this may require a very broad view
to be taken on a regional basis in the first instance. A regional cell could then be subdivided
into smaller cells once the basic coastal processes had beenestablished, and so on, with
decreasing cell sizes until the cell in question becomes the specific one of the project itself. It
is only in this way that the impact of new works in the coastal zone can be evaluated
satisfactorily or long-term planning undertaken. The basic tools of the coastal engineer are
still fairly limited and comprise cross-shore structures (such as groins, jetties,spurs),
shore-parallel structures (offshore breakwaters, seawalls, revetments and dikes), headland
structures and artificial beach nourishment (Fig. 3).
Fig. 3 Schematic presentation of various shore protection measures
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- Groins generate considerable changes in wave and circulation patterns but their basic
function to slow down the rate of littoral drift is sometimes overlooked. In theabsence of
beach nourishment, groins can redistribute the existing supply and, in a continuous littoral
system, may be expected to create a deficiency at the downdrift end where the uncontrolled
drift rate is re-established. Without an adequate supply of beach material, groins are of
limited value. In addition to controlling the rate of drift, groins are also used extensively to
control thedistribution of material along a frontage and to limit the temporary effects of drift
reversal. There are unfortunately many examples where either bad design or failure to
provide for the downdrift consequences has resulted in an adverse effect on the coastline. In
other instances, failure to maintain groin systems might be worser than having no groins at all
(see also, Fleming, 1990).
- Offshorebreakwaters are usually provided either to reduce wave energy at shoreline
structures or to modify the wave climate and enhance sediment transport patterns so as to
improve beach levels and create desirable beach features, such as salients. Offshore
breakwaters can be shore-connected or detached, submerged or emerging, longshore or
oblique (Pilarczyk&Zeidler, 1996).
- Perched beach is a...