Beach replenishment/nourishment

Category: NBS FOR EROSION CONTROL - Combined living/not living approach / NBS for erosjonsreduksjon - kombinerte levende/ikke levende materialer

Description

This method is widely used for protecting beaches from shoreline erosion even if is not an inexpensive measurement (Dean, 2003). It is defined as the process of mechanically or hydraulically placing sand directly on an eroding shore to restore or form and subsequently maintain an adequate protective or desired recreational beach. In some cases, it is used for expanding an existing narrow beach. The result of this simple measure is a wide aesthetic beach without interfering with natural, physical beach processes (Walton, 1977). It represents a good alternative to the grey constructions used to protect from coastal erosion. A review on the ecological effects on the ecosystem of using beach nourishment on coastal shorelines is provided by Speybroeck et al. (2006).

Advantages

  • Creation of additional space for recreational purposes;

  • dissipation of wave energy across the surf zone and protection of upland structures and infrastructures from storm surges or tsunami (Speybroeck et al., 2006);

  • fast creation of a natural equilibrium for sediment and water dynamics, which lasts for long time (Peterson et al., 2000);

Disadvantages

  • High costs and intensive labor;

  • Maintenance required every few years;

  • Not effective against major storms or waves with high energy.

Figure 1. Nourishment on Goleta Beach, CA (source: http://explorebeaches.msi.ucsb.edu/)


Design methods

For an effective and lasting beach nourishment measure, some requirements are needed. The sand to be used should be compatible with the native sand. In some cases, to minimize the amount of sand needed it can be used a sand with an average grain size higher than that of the existing sand (Raudkivi and Dette, 2002). The design of the beach nourishment is based on historical data of background erosion or predicted values of erosion that can occur in that zone. The design level can vary from very elementary to very detailed depending on the type of analysis to predict the performance of the measure. At elementary design level the material available is simply placed on the beach thereby advancing seaward. At detailed level numerical models can be used for predicting the evolution of the beach nourishment in different directions during the time (Dean, 2003).    

There are two nurishment strategies: classic (profile) nourishment and the dune nourishment. Profile nourishment involves the deposition of the sediment along the entire interidial zone, while dune nourishment consists in applying the sand only on the waterline without expanding the width of the dry beach. When the aim of the beach nourishment is to create a recreational area along the shoreline, the dune nourishment is not appropriated ( Speybroeck et al., 2006).

The volume of material needed depends mainly on the elevation of the existing beach relative to the predicted water level during a major coastal storm event and on the level of protection desired. The lower the existing beach level and the higher the predicted water level during the storm, the greater the volume of sediment needed for a certain level of protection (Massachussets Office of Coastal Zone Management CZM, 2013). In order to calculate the volume of material needed, the evolutionary process of the beach nourishment should be considered. In fact, after a beach nourishment, due to the waves action the profile of the beach will evolve toward a condition of equilibrium. The time required for this equilibrium in important for a good design of the measure. For a particular amount of material, the equilibrium depends mainly on the sediment size used (fine or coarse sand), the depth of the closure, the berm height and the beach added width. Depending on the intensity of protection required, from the schematization of the profile evolution for fine and coarse sediment is possible to judge a successful measurement (Figure 2).

Figure 2. Beach profiles associated to a beach nourishment project: original profile, initial placed profile and adjusted profiles as result of nourishment with coarse sand and fine sand (Dean, 2003).

 

Two techniques can be used for the application of sediment on the coastal shoreline.

Rainbow spraying technique: it consists in taking sand from the nearby seabed with a dredger and then discharging the sand along the needed shore (Figure 3). Before starting the so called "borrow area", the offshore area from which the sediment is removed are individuated (Figure 4). During the design of a beach nourishment, the search for the location of one or more borrow areas with adequate quantities of suitable quality sand should be defined (Dean, 2003). This technique is very fast (few hours until the required volumes have been delivered on the shoreline) and is usually performed during summer time, when weather conditions are most favourable for sailing. However, the sand taken from the seabed increases the salt percentage that can damage the vegetation (Adriaanse and Coosen, 1991). 

Figure 3. Rainbowing sandy material around Pevensey Bay (Pevensey Coastal Defence Ltd, UK http://www.pevensey-bay.co.uk/recharge.html)
Figure 4. Beach and profile nourishment (Dean, 2003)

Pipelines technique: is the most commonly used method and it consists in supplying sand by means of pipelines. The sand is taken under pressure and directly injected into the interested zone (Figure 5). With this technique is possible to concentrate the coarsest sand fraction when needed, but this can cause elevated turbidity of the coastal water (Speybroeck et al., 2006).

Figure 5. Pumping Sand onto Burleigh Beach - Tallebudgera Creek Dredging and Burleigh Beach Nourishment - 2015 - Neumann Contractors. (https://www.neumanncontractors.com.au/projects/dredging/tallebudgera-creek-dredging-2015)


Functional suitability criteria

Type of movement

Descriptor Rating Notes
Fall 2 Protection measure for shoreline erosion.

Removing causes of the problem is necessary.
Topple 1
Slide 5
Spread 1
Flow 4

Material type

Descriptor Rating Notes
Earth 4 Only used on debris material (sand).

Removing causes of the problem is necessary.

Only used on sand.
Debris 9
Rock 4

Depth of movement

Descriptor Rating Notes
Surficial (< 0.5 m) 10 Highly effective for surficial soil

Removing causes of the problem is necessary.
Shallow (0.5 to 3 m) 4
Medium (3 to 8 m) 1
Deep (8 to 15 m) 0
Very deep (> 15 m) 0

Rate of movement

Descriptor Rating Notes
Moderate to fast 1 More appropriate for slow wave flows and not effective against major storms or waves with high energy
Slow 3
Very slow 6
Extremely slow 9

Ground water conditions

Descriptor Rating Notes
Artesian 9 Applicable irrespective of groundwater conditions, but mostly used along coastal shorelines (from low to high water level)
High 4
Low 3
Absent 2

Surface water

Descriptor Rating Notes
Rain 5 This measure is typically used for protecting slopes from sea water waves. It can also provide protection against rain/stormwater erosion.
Snowmelt 3
Localized 5
Stream 4
Torrent 4
River 5

Reliability and feasibility criteria

Criteria Rating Notes
Reliability 8 Reliable according with a correct installation
Feasibility and Manageability 8 Easy installation with the proper equipment. Requires maintenance every few years

Urgency and consequence suitability

Criteria Rating Notes
Timeliness of implementation 8 Fast installation and immediate effectiveness
Environmental suitability 8 Beach nourishment consists of sediments compatible with the native sand
Economic suitability (cost) 4 High cost for equipment and labour. Maintenance is needed frequently

References

  • Adriaanse LA, Coosen J. 1991. Beach and dune nourishment and environmental aspects. Coastal Engineering 16: 129–146.
  • Dean, R. G. (2003). Beach nourishment: theory and practice (Vol. 18). World Scientific Publishing Company.
  • Peterson CH, Hickerson DHM, Johnson GG. 2000a. Short-term consequences of nourishment and bulldozing on the dominant large invertebrates of a sandy beach. Journal of Coastal Research 16(2): 368–378.
  • Raudkivi AJ, Dette H-H. 2002. Reduction of sand demand for shore protection. Coastal Engineering 45: 239–259 
  • Speybroeck, J., Bonte, D., Courtens, W., Gheskiere, T., Grootaert, P., Maelfait, J. P., ... & Lancker, V. V. (2006). Beach nourishment: an ecologically sound coastal defence alternative? A review. Aquatic Conservation: Marine and Freshwater Ecosystems, 16(4), 419-435.
  • Walton, T. L. (1977). Beach nourishments in Florida and on the lower Atlantic and Gulf Coasts (No. 2). Coastal and Oceanographic Engineering Laboratory.

back to top