The second ‘Sandpit’ report — A report from a large group of independent European scientists concerned with the impact of Offshore Aggregate Dredging

The Sandpit report for Year 2 is the second research based report carried out by WL/Delft Hydraulics. Its overall objective is to attempt to develop reliable prediction techniques for offshore aggregate dredging and to give guidelines to simulate, better understand, predict and mitigate the damaging effects of the process. The second Scientific Report was recently published and is based upon research carried out in the second year. The report for Year 3, 2005 is still in draft form, but in essence appears substantially much the same as its predecessor. The final report in the series has yet to be uncovered, but it could be that its publication is still awaited.

This most recently available published report that is to be found in full at http://sandpit.wldelft.nl/reportpage/reportpage.htm is a detailed and lengthy study, quite complex in parts, and far too bulky to be placed place in full here. But to provide the main points of interest, Peter Waller has extracted and summarised the main points and has also supplied the conclusions he has arrived at as a result of his study. Here is his précis.

SCIENTIFIC REPORT OF SANDPIT PROJECT, April 2003-APRIL (2004 YEAR 2) MAY 2004, SANDPIT EC FIFTH FRAMEWORK PROJECT No. EVK 3-2001-00056

Scientific Report of Year 2

The current scientific report is a summary and appraisal of the work done in Year 2 of the investigation. Separate management and progress reports of year 2 have also been produced. The report states that “Most of the leading European specialists on morphological modelling using 2DH and 3D models are participating in the project with the aim of validating their model systems and, hence, quantifying the impacts of sand mining.”

Dirk-Jan R. Walstra, Leo C. van Rijn and Arjen Klein (WL/Delft Hydraulics) in their contribution to the report noted that:

“Coastal erosion is expected to increase in many European countries owing to sea level rise. This will lead to an increased demand for sand for the nourishment of beaches and dunes. Mining of sand from the middle and lower shore face (depths of 10 to 30 m) in large-scale mining pits will be required to meet this increased demand in future. It is expected that Large-scale mining by dredging artificial sand pits or by removing existing sand banks will have a significant impact on the near-field and far-field morphologymorphology The science of form. In biological terms, it is the area of knowledge which deals with the form of plants and animals. Hence coastal morphologists — (sometimes referred to as coastal geomorphologists): those espousing or dealing with coastal geomorphology, in our treatise the changes of our coastline. (increased coastal erosion)”.

“The SANDPIT-project of the 5th framework of the EU Community Research Programme, which commenced in April 2002, aims to address this problem. The general objective of the SANDPIT-project is to better understand and reliably predict the morphological behaviour of large-scale sand mining pits and the associated sand transport processes at the middle and lower shore face. As part of the project a number of benchmark tests were defined (both laboratory and field). These tests are used to establish the efficacy of morphodynamic models in predicting the behaviour of large-scale mining pits and so to contribute to improved coastal zone management.”

“The overall objective of the SAND PIT project is to develop reliable prediction techniques and guidelines to better understand, simulate and predict the morphological behaviour of large-scale sand mining pits/areas and the associated sand transport processes at the middle and lower shore face and the surrounding coastal zone.”

The report notes:

” … that no cases were reported in which coastal problems have been encountered as a proven result of offshore extractions”. Yet it recognises that there is an impact on coastal erosion when dredging takes place up to 15m below mean low water, though little, if any at 18m and beyond

Note: By “no cases were reported” we assume that the loss of the East Anglian coastline since offshore aggregate dredging commenced and the loss of sand banks were not reported to them, nor had they noted the Eurosion Report and many others under ‘Scientific Studies from around the world’ on the erosion resulting from offshore sand and gravel dredging’ to be found on our website. This statement “no cases were reported” should therefore not be taken to imply that there were no such cases to report.

The use of ‘up to 15m below mean low water, though little, if any at 18m and beyond’ is also confusing, as this could be interpreted as meaning 15m and 18m horizontal distance from the low tide mark, which is obviously not the case. It would be more meaningful to have it given as “up to 15m water depth below that of mean low water, though little, if any, at 18m depth and beyond”.

The North Sea and Mediterranean Seas are identified where:

” … material dredged will be used for nourishing beaches and coastal dunes as a result of more erosion caused by sea level rise plus large engineering projects and house and industrial building projects.”

Note: Are we to assume that “large engineering projects and house and industrial building projects.” includes the use of marine dredged aggregate in their construction?

The volume of dredged material required over the next 10 to 20 years is estimated to be 100 to 1,000 million m3 for countries around the North Sea, the implication being that existing dredging areas will need to be expanded and new ones found.

The report notes that:

” … large-scale mining pits will have a significant impact on the near-field and far-field (up to the coast) flow and wave patterns; the flow velocities inside the pit will be reduced and the wave heights may also be reduced, depending on the depth of the pit. As a consequence, the sand transport capacity inside the pit will decrease and sediments will settle in the pit area, resulting in deposition. Thus, the pit will act as a sink for sediments originating from the surrounding areas and depending on the local flow and wave patterns. Hence, erosion of the sea floor will take place in the (immediate) surrounding of the pit.”

There is no indication from where sediment originates from to fill dredged pits, but there is an implication that pits may migrate as cohesiveness is compromised.

The report also recognises that:

“due to the large scale of future dredging activities that the location of dredging areas need to be situated in locations to minimise the effects of near shore coastal erosion.”

It questions the accuracy of the “computed sand transport rates”, and adds that “model verification and validation based on detailed field data is lacking in most cases.” and notes that the “main reason for this is that detailed field data sets of sand transport in offshore (deep water) conditions are scarcely available.”

Under the section ‘Modelling of sand banks and sand waves’, the report states that if a sand bank is disturbed its cohesiveness may become compromised thus making it unstable and maybe prone to collapse and or move. Furthermore, that sand waves may migrate due to the “presence of the steady current induced by the superimposition of different components of the tide”.

“Sand waves are regular sea bed patterns of large spatial scale which occur on non-cohesive sandy bottoms. The spatial scale of such sedimentary structures is characterized by a wavelength of 100-800 m and a wave height of 1 – 5 m. In most cases, sand wave crests are perpendicular to the prevailing spring tidal current (Stride, 1982). Sand wave migration can cause important changes in bottom morphology and, in turn, can affect the stability of oil pipelines, offshore constructions, as well as submarine cables. In some cases, such as that of the Rotterdam harbour, it can compromise the navigation. A new model of the growth and migration of sand banks and tidal flow has been established”.

Comment:

This gives researched back up to the assertion of our claim “The sand sea bed in this location is mobile and moves to infill the dredged areas this sand sea bed movement then eventually causes beach draw downdraw down The process by which tides and wave motion remove (draw down) material from a beach and pull it out to sea. A sandy beach experiencing draw down is thus denuded of its sand. The process can be natural (i.e. winter storms) or can be artificially caused (e.g. aggregate dredging, whereby the dredging of sand and gravel offshore causes sand to be drawn down from the beach in order to replace the material which has been dredged).” which was given by Mike King in contradiction to HAML, when in respect of Areas 401 and 402 licensing renewal applications HAML claimed “the sea bed is not mobile and sand from the surrounding seabed areas, sand banks or beaches does not infill the dredged areas – but natural seabed anchor patterns are soon re-established”.

Additionally the report notes:

“Mathematical modelling requires model calibration and validation using consistent data sets. The development and improvement of accurate models for the prediction of shore face and coastal processes on short and long term scales due to natural and human-induced changes have been stressed; these models must be tested and verified against field data, requiring sharing of facilities and equipment at the international level”

“Field data on shore face processes during tides and storms is essential for improvement of our knowledge on these processes, for improvement of numerical models and, hence, for better design of sand mining projects: . . . ”

“Sand transport problems in complex morphodynamic systems, such as shore face systems (with currents and waves) are too complicated to be solved on a national basis; . . ”

The following management questions are noted in the report:

“What is the optimal design of large scale sand mining operations? Design options to be considered are location, dimension, shape and orientation of the sandpit as well as excavation method. The scale of sand mining concerns 10’s to 100’s of million cubic meters per location. The design optimum depends on the specific context of sand mining which determines acceptable limits to an impact.”

“A rational Coastal Zone Management (CZM) needs to be based on an integrated analysis of the specific context. Related to sand mining, the overarching CZM question is: What are the effects of large scale sand mining on the physical and ecological environment, on the functional uses and on institutional arrangements; and vice versa? A rational CZM will aim for a rational decision making process that is transparent and reproducible. The (Vague) strategic CZM objectives must be translated into (concrete) operational objectives.”

Under ‘Environment’ it states “The knowledge, methods, models and guidelines that will be developed in this project are aimed at designing sand mining projects that have a maximum technological performance and minimum impact on the environment (ecology)”.

Under ‘Ecological Effects’ it gives:

  • “Aggregate extraction removes the sea bed habitat and destroys the associated biota.”
  • “Guidelines for the assessment and management of marine sediment extraction have been refined.”
  • “Management frame work and ecological state indicators have been developed.”

Peter’s observations made from his study of the document are:

(1) The report would appear to question the validity and conclusions of H. R. Wallingford’s Southern North Sea Sediment Transfer Study; similarly the statements of Halcrow & Co, in the Kelling to Lowestoft Ness SMP, which claims that offshore aggregate dredging impact on coastal erosion is ‘unclear’.

(2) Dredging, laying pipelines, putting in place wind turbines etc. disturbs the cohesiveness of sand banks and the sea bed so causing collapse and movement, which is very evident at Scroby.

(3) Coastal/onshore and off-shore processes and systems are clearly linked.

(4) Dredging has disturbed the ‘natural balance’, or is causing an ‘imbalance’ which nature is trying to rectify by causing more erosion.

(5) It appears from the content that some of the people, institutions and organisations involved may have contributed to the EUROSION Report.

(6) DEFRA’s and the EA’s stance on the dredging issue appears highly questionable, as it would be most surprising that they were/are unaware of this report. Even a non-expert can clearly see and understand the potential implications.

Final comment from Pat Gowen:

From the most recent Sandpit 2005 report comes this clear and simplified drawing of cause and effect. We feel that this is readily understandable, even to DEFRA.

Effects of sand mining pit on shoreline

 

We seem to be experiencing a problem in locating or getting our hands on the final Sandpit Report, which must surely be out by now. I wonder if this is seen as a ‘hot potato’ to be toned down or censored, as happened to the Eurosion Report to be found on this website at www.marinet.org.uk/mad/scientificstudies.html#eep . This has since been sanitized and replaced by the same report but with all maps and mention of the erosion of the North Norfolk Coast due to offshore aggregate dredging removed.

This new research questions the validity of the claims made by BMAPA, DEFRA and the EA and BMAPA that Offshore Aggregate Dredging does not produce coastal erosion, and points out that the assumptions hitherto made by computer modelling cannot be used without actual on site practical research to back the suppositions up.

It will be interesting to see if our government bodies now heed this report, and are prepared to venture into meaningful research that would conclusively prove the already obvious link between marine dredging and coastal and sand bank erosion. Inasmuch as it would mean them abruptly changing their position and entertaining compensation claims from those who have lost their homes, businesses and amenities, in addition to the loss of considerable income, such consideration is felt to be unlikely.

Pat Gowen, 24th February 2008

More on the Sandpit Report

The Sandpit draft report for Year 3 (6th February 2005) has been located by Peter Waller, who will soon have a copy of the final published version. The content is in the main a repetition of the points made in the earlier version, but with clearer meaning and with a number of vital considerations and recommendations included.

The full 137 page document draft SAND TRANSPORT AND MORPHOLOGY OF OFFSHORE SAND MINING PITS is to be found as a pdf document whilst an even larger tome is to be seen by going to http://sandpit.wldelft.nl/reportpage/right/progressreports.htm giving the Management, Progress and Scientific Reports. Sandpit has been composed by 30 renowned individuals from 17 different organisations and universities, and was sponsored by the European Commission. The comprised end-users, field experimenters and researchers from various leading research institutes and universities in Europe with an established strength and of a balanced composition, linking expertise in basic physical processes (experimental and modelling research) to that in coastal engineering applications.

Whilst a wealth of information exists in the documents and in the references, both contain complex date and terminology somewhat difficult to comprehend by non coastal geomorphologists, but a glossary of the acronyms and term is appended that assists.

The focus of the SANDPIT project was mainly on the physical aspects of sand transport. Efforts on aspects of fine sediments were limited. Ecological aspects were studied on the basis of a literature review only. An economical assessment of cost was not scheduled. The development of acceptability criteria for any assessed effect was considered to be outside the scope of SANDPIT. Considering the availability of data, SANDPIT concentrated on the design options related to the location.

Here follows quotes from the report of direct relationship interest to MARINET’s long held concerns, first with the SANDPIT focus on the central problem:

“How does the location of sand mining (in terms of water depth and distance from the shore) influence the various effects of large scale sand mining? Give a quantitative estimate of probable effects”.

The justification for the investigation reads:

“Given the scale of these undertakings, the volume of sand required in the near future (10 to 20 years) will be of the order of 100 to 1000 million m3 per country surrounding the North Sea. To meet these demands, the existing areas for mining of sand need to be extended considerably and new potentially attractive areas should be explored and exploited. Massive mining of sand may take place by dredging in artificial sand pits or channels (also navigation channels) or by removal (dredging) of existing large-scale sand banks/shoalsshoal A sandbank or sandbar that makes the water shallow in the offshore zone (middle and lower shoreface).

Large-scale mining pits will have a significant impact on the near-field and far-field (up to the coast) flow and wave patterns; the flow velocities inside the pit will be reduced and the wave heights may also be reduced, depending on the depth of the pit. As a consequence, the sand transport capacity inside the pit will decrease and sediments will settle in the pit area, resulting in deposition. Thus, the pit will act as a sink for sediments originating from the surrounding areas and depending on the local flow and wave patterns. Hence, erosion of the sea floor will take place in the (immediate) surrounding of the pit. This may lead to a direct loss of sediment from the nearshore zone (beaches, see Figure 1 top). Indirect effects result from the modification of the waves moving and refracting over the excavation area (pit), which may lead to modification of the nearshore wave conditions (wave breaking) and hence longshore currents and sediment transport gradients and thus to shoreline variations (see Figure below).

Drawing showing sediment transport

 

“Considering the massive scale of future mining of sand and hence the large spatial scales that will be affected by the mining activities, the mining areas need to be situated in the offshore shoreface zone to minimise the effects of nearshore coastal erosion” and ” Considering the massive scale of future mining of sand and hence the large spatial scales that will be affected by the mining activities, the mining areas need to be situated in the offshore shoreface zone to minimise the effects of nearshore coastal erosion”.

The following series of questions were posed. Concentrating on the Near Field and the Far Field CZM impacts, the set of middle level questions were distinguished (with the attempts to answer later in the treatise):

On the Near Field (Navigation, Fisheries, Offshore Structures and a Sustainable Ecosystem):

1. Will an offshore mining pit modify the local flow and wave fields in such a way that the transport regime and the large-scale bed forms (sand banks) in the direct vicinity are influenced? Can the magnitude of an effect be quantified?
2. Will the mining pit act as a sediment sink and thereby have a particularly marked impact on the sea bed immediately adjacent to the pit? Can the magnitude and extent of this impact be quantified? How can this impact be minimised?
3. Will sand banks that have been mined away, return within a period of 50 years, where does the sand come from and will it affect other nearby sand banks?
4. Will sand mining destroy the local benthic organisms which may be environmentally and commercially important? Can the effect on and recovery of these organisms be quantified? Are any mitigation measures possible?

Concentrating on the Far Field (Flood Protection, Coastal Maintenance, Fisheries and a Sustainable Ecosystem) the following set of middle level questions are distinguished

5. Will a large-scale mining pit affect the overall tide- and wind-induced flow regime in a coastal sea including nearby tidal inlets? Can the effect be quantified?
6. Will the mining pit allow more wave energy to reach the coastline through mechanisms such as reducing nearshore wave limiting conditions (e.g. by removing nearshore sand banks) or by acting as a lens to focus wave energy on the coastline? Can the magnitude and extent of this impact be quantified and to what degree of accuracy?
7. Will an offshore mining pit (removal of sand below bed or removal of sand banks) act as a sediments sink and what impact will it have on nearshore sediment transport regimes and will it lead to increased coastal erosion? Can the magnitude and extent of this impact be quantified and to what degree of accuracy?
8. Will the fines (mud) released during large-scale mining process affect the overall budget of fines in the surrounding seas and the import of fines into adjacent tidal inlets and back-barrier basins? Will it result in an increase of turbidity affecting oyster farming or spawning areas?
9. What measures can be taken to minimise the negative impacts that sand mining may have on the coastline? Can parameters such as minimum dredge depth and distance from the shore be defined?
10. Measures to minimise the negative impacts of sand mining on the coastline will have cost implications. How does the cost per m3 of sand depend on the location (depth and distance from shore) and dimensions of the pits?

Each of these middle level questions can be extended with the question on what time scales (short term / long term) a potential effect may be of importance.

SANDPIT approach

These selected (middle level) CZM (Coastal Zone Management) questions represent the basis for defining a set of detailed research questions referring to underlying process parameters. The process parameters will be the subject of quantitative assessment by measurements (WP3) and modelling (WP4) within SANDPIT. The final results will be integrated as much as possible in terms of CZM-Indicators, to answer the overarching CZM question (WP2). Quantitative estimates from SANDPIT may provide a starting point for future discussions on acceptability criteria by CZM authorities.

The CZM questions are here translated into various research questions to be addressed in the SANDPIT project.

CZM questions Near Field Research questions Indicators

1. Will an offshore mining pit modify the local flow and wave fields in such a way that the transport regime and the large-scale bed forms (sand banks) in the direct vicinity are influenced?

a. what is the change in maximum tidal current velocity due to the presence of a dredged pit (or dredged sandbank) of given size?
b. what is the change in wave height during a storm due to the presence of a pit of given size?
c. what are the effects of modified flow and wave conditions on the local sand transport capacity?
d. what is the influence area?

i. maximum current velocity
ii. maximum wave height
iii. net annual sand transport rates

2. Will the mining pit act as a sediment sink and thereby have a particularly marked impact on the sea bed immediately adjacent to the pit. Can the magnitude and extent of this impact be quantified? How can this impact be minimised?

a. what is the sand transport regime in relation to the current and wave regime outside the dredged pit (or dredged sandbank)?
b. what is the effect of (modified) bed forms and (modified) particle size on the sand transport regime outside the pit?
c. what is the gross and net annual sand transport outside the pit?
d. what is the amount of sand trapped in a pit of given size per year and over 50 years?
e. what is the erosion on the flanks of the pit per year and over 50 years?
f. what are the net migration rates in longshore and in cross-shore direction?
g. what should be the location and dimensions of the pit to minimise these effects?

i. annual infill volume
ii. erosion length scales
iii. net migration rates in longshore and in cross-shore direction
iv. optimum pit dimensions; distance to shore

CZM questions Far Field Research questions Indicators

3. Will a large-scale mining pit affect the overall tide- and wind-induced flow regime in a coastal sea including nearby tidal inlets?

a. what is the effect of a large-scale mining pit of given size (or dredged sand bank) on the nearshore tide-induced and wind-induced currents?
b. what is the influence area of a large-scale dredged pit (or dredged bank) on the flow regime?

i. tidal rangestidal range The difference in height between high and low tide
ii. peak tidal currents
iii. maximum wind induced currents

4.Will a large-scale mining pit allow more wave energy to reach the coastline through mechanisms such as reducing nearshore wave limiting conditions (e.g. by removing nearshore sand banks) or by acting as a lens to focus wave energy on the coastline? Can the magnitude and extent of this impact be quantified and to what degree of accuracy?

a. what is the effect of a large-scale dredged pit (or bank) of given size on the nearshore wave field?
b. what is the influence area of a large-scale mining pit (or bank) on the wave climate?

i.nearshore wave spectrum (edge of surf zone; -8m and -5m depth contours)

5.Will an offshore mining pit (removal of sand below bed or removal of sand banks) act as a sediments sink and what impact will it have on nearshore sediment transport regimes and will it lead to increased coastal erosion? Can the magnitude and extent of this impact be quantified and to what degree of accuracy?

a. what is the effect of a dredged pit or sand bank on the gross and net annual longshore sand transport in the surf zone?
b. what is the effect of a dredged pit or sand bank on the gross and net annual crosshore sand transport at edge of the surf zone?
c. what are the changes in net annual cross-shore and longshore transport rates in relation to the sand volume in the nearshore zone on a coastal length scale comparable to the scale of the mining area?
d. what is the optimal location and what are the optimal dimensions of the mining area (pit or sand bank) to minimise its effect on the coastline?
e. How far offshore must a mining area be situated before its effect on the coast can be ignored?

i. net annual longshore transport in surf zone
ii. net annual crossshore transport at edge of surf zone (-8m and -5m depth contours)
iii. sand volume in predefined zone
iv. shoreface slope between -8m depth contour and coastline
v. beach width

CZM questions Far Field Research questions Indicators

6. Will a large-scale mining pit affect the overall tide- and wind-induced flow regime in a coastal sea including nearby tidal inlets?

a. what is the effect of a large-scale mining pit of given size (or dredged sand bank) on the nearshore tide-induced and wind-induced currents?
b. what is the influence area of a large-scale dredged pit (or dredged bank) on the flow regime? viz 1) tidal ranges, 2) peak tidal currents and 3) maximum wind induced currents

7. Will a large-scale mining pit allow more wave energy to reach the coastline through mechanisms such as reducing nearshore wave limiting conditions (e.g.by removing nearshore sand banks) or by acting as a lens to focus wave energy on the coastline? Can the magnitude and extent of this impact be quantified and to what degree of accuracy?

a. what is the effect of a large-scale dredged pit (or bank) of given size on the nearshore wave field?
b. what is the influence area of a large-scale mining pit (or bank) on the wave climate?

i. nearshore wave spectrum (edge of surf zone; -8m and -5m depth contours)

8. Will an offshore mining pit (removal of sand below bed or removal of sand banks) act as a sediments sink and what impact will it have on nearshore sediment transport regimes and will it lead to increased coastal erosion? Can the magnitude and extent of this impact be quantified and to what degree of accuracy?

a. what is the effect of a dredged pit or sand bank on the gross and net annual longshore sand transport in the surf zone?
b. what is the effect of a dredged pit or sand bank on the gross and net annual crosshore sand transport at edge of the surf zone?
c. what are the changes in net annual cross-shore and longshore transport rates in relation to the sand volume in the nearshore zone on a coastal length scale comparable to the scale of the mining area?
d. what is the optimal location and what are the optimal dimensions of the mining area (pit or sand bank) to minimise its effect on the coastline?
e. How far offshore must a mining area be situated before its effect on the coast can be ignored?

i. net annual longshore transport in surf zone
ii. net annual crossshore transport at edge of surf zone (0-8m and -5m depth contours)
iii. sand volume in predefined zone
iv. shoreface slope between -8m depth contour and coastline
v. beach width

7.7 Ecological effects

“One of the greatest challenges when determining the impact benthic communities face from dredging is the lack of baseline data and overall context in which benthic communities can be compared. Compilation (databases) and analysis of historical benthic data sets for various regions would provide baseline information for use in future biological studies”.

“More knowledge should become available about the ecological relationship between the unique habitats of sand ridge, shoalshoal A sandbank or sandbar that makes the water shallow and bank features and resident benthic communities that live in those habitats. Sand sources such as ridges, shoals and banks that are used repeatedly may require ongoing biological and physical monitoring to alleviate adverse impacts. These features tend to be focal points for various fisheries, both recreational and commercial”.

“Altering the physical characteristics of these areas (grain size, waves, currents and bathymetrybathymetric Bathymetry, the depth of the seabed, analogous to topography (on land). A bathymetric reading or survey is therefore a measurement of the depth of the seabed. Such a survey is usually conducted acoustically.) could be detrimental for various fish species. Areas that are often selected as potential sand resources sites are in many cases used by fish as migration corridors, habitat for juvenile development, and spawning grounds. Activities that adversely influence these features, through disturbances in migration patterns and changes in substrate, water quality, or acoustic parameters, can directly result in a decrease in benthic communities and in fisheries”.

The proposed extraction area should be identified by geographical location, and described in terms of:

  • the bathymetry and topography of the general area
  • the distance from the nearest coastlines
  • the geological history of the deposit
  • the source of the material
  • type of material
  • sediment particle size distribution
  • extent and volume of the deposit
  • the stability and/or natural mobility of the deposit
  • thickness of the deposit and evenness over the proposed extraction area
  • the nature of the underlying deposit, and any overburden
  • local hydrography including tidal and residual water movements
  • wind and wave characteristics
  • average number of storm days per year
  • estimate of bed-load sediment transport [quantity, grain size, direction]
  • topography of the seabed, including occurrence of bedforms
  • existence of contaminated sediment and their chemical characteristics
  • natural [background] suspended sediment load under both tidal currents and wave action

Description of the biological setting

The biological setting of the proposed extraction site and adjacent areas should be described in terms of – the flora and faunafauna The animals characteristic of a region, period, or special environment within the area likely to be affected by aggregate dredging , (e.g. pelagicpelagic The ecological area consisting of the open sea away from the coast and the ocean bottom. The pelagic zone contains organisms such as surface seaweeds, many species of fish and sharks and some mammals, such as whales and dolphins. Pelagic animals may remain solely in the pelagic zone or may move among zones. and benthic community structure) taking into account temporal and spatial variability;

  • information on the fishery and shell fishery resources including spawning areas with particular regard to benthic spawning fish, nursery areas, over-wintering grounds for ovigerous crustaceans and known routes of migration;
  • trophic relationships, (e.g. between the benthos and demersaldemersal Living on the seabed fish populations by stomach content investigations)
  • presence of any areas of special scientific or biological interest in or adjacent to the proposed extraction area, such as sites designated under local, national or international regulations (e.g. RamsarRAMSAR The Convention on Wetlands is of International Importance especially as Waterfowl Habitat http://ramsar.org (Ramsar Convention or Wetlands Convention) was adopted in Ramsar, Iran in February 1971 and entered into force in December 1975. The Convention covers all aspects of wetland conservation and wise use. The Convention has three main 'pillars' of activity: + the designation of wetlands of international importance as Ramsar sites www.wetlands.org/RDB/quick.html + the promotion of the wise-use of all wetlands in the territory of each country + and international co-operation with other countries to further the wise-use of wetlands and their resources. The Convention's Contracting Parties have assumed a wide range of related obligations. As of December 2003 there were 138 Contracting Parties to the Convention http://ramsar.org/key_cp_e.htm, with 1,328 Ramsar sites covering over 111 million hectares. sites, the UNEP ‘Man and the Biosphere’ Reserves, World Heritage sites, Marine Protection Areas (MPA’s) Marine Nature Reserves, Special Protection Areas (Birds Directive) or the Special Areas of Conservation (Habitats Directive).

Description of the proposed aggregate dredging activity

The assessment should include, where appropriate, information on:

  • the total volume to be extracted
  • proposed maximum annual extraction rates and dredging intensity
  • proposed maximum annual extraction rates and dredging intensity
  • aggregate dredging equipment to be used
  • spatial design and configuration of aggregate dredging (i.e. the maximum depth of deposit removal, the shape and area of resulting depression)
  • substrate composition on cessation of aggregate dredging
  • proposals to phase (zone) operations
  • whether on-board screening (i.e. rejection of fine or coarse fractions) will be carried out
  • number of dredgers operating at a time
  • routes to be taken by aggregate dredgers to and from the proposed extraction area
  • time required for aggregate dredgers to complete loading
  • number of days per year on which aggregate dredging will occur
  • whether aggregate dredging will be restricted to particular times of the year or parts of the tidal cycle
  • direction of aggregate dredging (e.g. with or across tide)

It may be appropriate when known to also include details of the following:

  • energy consumption and gaseous emissions
  • ports for landing materials
  • servicing ports
  • on-shore processing and onward movement
  • project related employment

Information required for physical impact assessment

To assess the physical impacts the following should be considered:

  • implications of extraction for coastal and offshore processes, including possible effects on beach draw down, changes to sediment supply and transport pathways, changes to wave and tidal climate
  • changes to the seabed topography and sediment type
  • exposure of different substrates
  • changes to the behaviour of bedforms within the extraction and adjacent areas
  • potential risk of release of contaminants by aggregate dredging, and exposure of potentially toxic natural substances
  • transport and settlement of fine sediment disturbed by the aggregate dredging equipment on the seabed, and from hopper overflow or on-board processing and its impact on normal and maximum suspended load
  • the effects on water quality mainly through increases in the amount of fine material in suspension
  • implications for local water circulation resulting from removal or creation of topographic features on the seabed
  • timescale for potential physical ‘recovery’ of the seabed

Information required for biological impact assessment

To assess the biological impact the following information should be considered:

  • changes to the benthic community structure
  • effects of aggregate dredging on pelagic biota
  • effects on the fishery and shell fishery resources including spawning areas with particular regard to benthic spawning fish, nursery areas, overwintering grounds for ovigerous crustaceans and known routes of migration
  • effects on trophic relationships (e.g. between the benthos and demersal fish populations)
  • effects on sites designated under local, national or international regulations (see above)
  • predicted rate and mode of recolonisation, taking into account initial community structure, natural temporal changes, local hydrodynamics and any predicted change of sediment type
  • effects on marine flora and fauna including seabirds and mammals
  • effects on the ecology of boulder fields/stone reefs

Interference with other legitimate uses of the sea

The assessment should consider the following in relation to the proposed programme of extraction:

  • commercial fisheries
  • shipping and navigation lanes
  • military exclusion zones
  • offshore oil and gas activities
  • engineering uses of the seabed (e.g. adjacent extraction activities, undersea cables and pipelines including associated safety and exclusion zones)
  • areas designated for the disposal of dredged or other materials
  • location in relation to existing or proposed aggregate extraction areas
  • location of wrecks and war-graves in the area and general vicinity
  • wind farms
  • areas of heritage, nature conservation, archaeological and geological importance
  • recreational uses
  • general planning policies for the area (international, national and local)
  • any other legitimate use of the sea

Evaluation of impacts

When evaluating the overall impact, it is necessary to identify and quantify the marine and coastal environmental consequences of the proposal. The EIA should evaluate the extent to which the proposed extraction operation is likely to affect other interests of acknowledged importance. Consideration should also be given to the assessment of the potential for cumulative impacts on the marine environment. In this context cumulative impacts might occur as a result of aggregate dredging at a single site over time, from multiple sites in close proximity or in combination with effects from other human activities (e.g. fishing and disposal of harbour dredgings).

It is recommended that a risk assessment be undertaken. This should include consideration of worst case scenarios, and indicate uncertainties and assumptions used in their evaluation.

The environmental consequences should be summarised as an impact hypothesis. The assessment of some of the potential impacts requires predictive techniques, and it will be necessary to use appropriate mathematical models. Where such models are used, there should be sufficient explanation of the nature of the model, including its data requirements, its limitations and any assumptions made in the calculations, to enable assessment of its suitability for the particular modelling exercise.

Mitigation Measures

The impact hypothesis should include consideration of the steps that might be taken to mitigate the effects of extraction activities. These may include:

  • the selection of aggregate dredging equipment and timing of aggregate dredging operations to limit impact upon the biota (such as birds, benthic communities and fish resources)
  • modification of the depth and design of aggregate dredging operations to limit changes to hydrodynamics and sediment transport and to minimise the effects on fishing
  • spatial and temporal zoning of the area to be authorised for extraction or scheduling extraction to protect sensitive fisheries or to respect access to traditional fisheries
  • preventing on-board screening or minimising material passing through spillways when outside the dredging area to reduce the spread of the sediment plume
  • agreeing exclusion areas to provide refuges for important habitats or species, or other sensitive areas

Evaluation of the potential impacts of the aggregate dredging proposal, taking into account any mitigating measures, should enable a decision to be taken on whether or not the application should proceed. In some cases it will be appropriate to monitor certain effects as the aggregate dredging proceeds. The EIA should form the basis for the monitoring plan.

Authorisation Issue

When an aggregate extraction operation is approved, then an authorisation should be issued in advance (which may take the form of a permit, licence or other form of regulatory approval). In granting an authorisation, the immediate impact of aggregate extraction occurring within the boundaries of the extraction site such as alterations to the local physical, and biological environment is accepted by the regulatory authority.

Notwithstanding these consequences, the conditions under which an authorisation for aggregate extraction is issued should be such that environmental change beyond the boundaries of the extraction site are as far below the limits of allowable environmental change as practicable. The operation should be authorised subject to conditions which further ensure that environmental disturbance and detriment are minimised.

The authorisation is an important tool for managing aggregate extraction and will contain the terms and conditions under which aggregate extraction may take place as well as provide a framework for assessing and ensuring compliance.

Authorisation conditions should be drafted in plain and unambiguous language and will be designed to ensure that:

  • the material is only extracted from within the selected extraction site
  • any mitigation requirements are complied with; and
  • any monitoring requirements are fulfilled and the results reported to the regulatory authority

Monitoring compliance with conditions attached to the authorisation

An essential requirement for the effective control of marine aggregate extraction is monitoring on a continuous basis of all aggregate dredging activity to provide a permanent record. This has been achieved in several ways e.g. an Electronic Monitoring System or Black Box. The information provided will allow the regulatory authority to monitor the activities of aggregate dredging vessels to ensure compliance with particular conditions in the authorisation.

The information collected and stored will depend on the requirements of the individual authorities and the regulatory regime under which the permission is granted e.g. EIA, Habitats, Birds Directives of the EU.

The minimum requirements for the monitoring system should include:

  • an automatic record of the date, time and position of all aggregate dredging activity
  • position to be recorded to within a minimum of 100 metres in latitude and longitude or other agreed co-ordinates using a satellite based navigation system
  • there should be an appropriate level of security
  • the frequency of recording of position should be appropriate to the status of the vessel i.e. less frequent records when the vessel is in harbour or in transit to the aggregate dredging area e.g. every 30 minutes and more frequent when dredging e.g. every 30 seconds

The above are considered to be a reasonable minimum requirement to evaluate the regulatory authority to monitor the operation of the authorisation in accordance with any conditions attached. Individual countries may require additional information for compliance monitoring at their own discretion.

The records can also be used by the aggregate dredging company to improve utilisation of the resources. The information is also an essential input into the design and development of appropriate environmental monitoring programmes and research into the physical and biological effects of aggregate dredging including combined/cumulative impacts (see section above).

Environmental Monitoring

Sand and gravel extraction inevitably disturbs the marine environment. The extent of the disturbance and its environmental significance will depend on a number of factors. In many cases it will not be possible to predict, in full, the environmental effects at the outset, and a programme of monitoring may be needed to demonstrate the validity of the EIA’s predictions, the effectiveness of any conditions imposed on the authorisation, and therefore the absence of unacceptable impacts on the marine environment.

The level of monitoring should depend on the relative importance and sensitivity of the surrounding area.

Monitoring requirements should be site specific, and should be based, wherever possible, on the findings of the EIA. To be cost effective, monitoring programmes should have clearly defined objectives derived from the impact hypothesis developed during the EIA process. The results should be reviewed at regular intervals against the stated objectives, and the monitoring exercise should then be continued, revised, or even terminated.

It is also important that the baseline and subsequent monitoring surveys take account of natural variability. This can be achieved by comparing the physical and biological status of the areas of interest with suitable reference sites located away from the influence of the aggregate dredging effects, and of other anthropogenic disturbance. Suitable locations should be identified as part of the EIA’s impact hypothesis.

A monitoring programme may include assessment of a number of effects. When developing the programme a number of questions should be addressed including:

  • what are the environmental concerns that the monitoring programme seeks to address?
  • what measurements are necessary to identify the significance of a particular effect?
  • what are the most appropriate locations at which to take samples or observations for assessment?
  • how many measurements are required to produce a statistically sound programme?
  • what is the appropriate frequency and duration of monitoring?

The regulatory authority is encouraged to take account of relevant research information in the design and modification of monitoring programmes. The spatial extent of sampling should take account of the area designated for extraction and areas outside which may be affected. In some cases, it may be appropriate to monitor more distant locations where there is some question about a predicted nil effect. The frequency and duration of monitoring may depend upon the scale of the extraction activities and the anticipated period of consequential environmental changes which may extend beyond the cessation of extraction activities.

Information gained from field monitoring (or related research studies) should be used to amend or revoke the authorisation, or refine the basis on which the aggregate extraction operation is assessed and managed. As information on the effects of marine aggregate dredging becomes more available and a better understanding of impacts is gained, it may be possible to revise the monitoring necessary. It is therefore in the interest of all concerned that monitoring data is made widely available. Reports should detail the measurements made, results obtained, their interpretation and how these data relate to the monitoring objectives.

From SANDPIT SAND TRANSPORT AND MORPHOLOGY OF OFFSHORE SAND MINING PITS

Process knowledge and guidelines for coastal management

The impact of a extraction pit on the coast can at the present stage of knowledge only be estimated in rough way from the available data of existing extraction pits made in the coastal waters of the USA, Japan, UK and The Netherlands. Four zones are distinguished and the impact of a pit in each zone is briefly described.

pit at foot of beachface (-2 to -5 m depth contour);

  • cheap and attractive method for sheltered coasts (mild wave regimes; small littoral driftlittoral sediment flow This is the flow or movement of sediment (sand, shingle or pebbles) along a beach or coastline. The flow or direction of movement is usually determined by the tidal and wave regime dominant in the area.);
  • infill from beachside and from seaside (annual infill rate is not more than about 3% of initial pit volume; infill rates are between 5 and 15 m3/m/yr, depending on wave climate; filling time scale is 20 to 30 years);
  • local recirculation of sand; no new extraction sand is added to beach system;

pit in upper shoreface zone (-5 to -15m depth contour);

  • relatively strong impact on inshore wave climate due to modified refraction and diffraction effects;
  • relatively strong modification of gradients of littoral drift in lee of pit resulting in significant shoreline changes (growth of beach salients);
  • relatively rapid infill of extraction pit with sediments from land side (beach zone); annual infill rates up to 20% of initial pit volume in shallow water (filling time scale is 5 to 10 years);
  • local recirculation of sediment; no new extraction sand is added to nearshore system;

pit in middle shoreface zone (-15 to -25m depth contour);

  • negligible impact on nearshore wave climate;
  • negligible effect on nearshore littoral drift;
  • no measurable shoreline changes;
  • new extraction sand is added to nearshore morphological system (nourishment);
  • infill of extraction pit mainly from landside with sediments eroded from upper shore face by near-bed offshore-directed currents during storm events; annual infill rate is about 1% of initial pit volume (filling time scale is 100 years);
  • trapping of mud in pits (negative ecological effect);
  • particle tracer studies show small but measurable transport rates, mainly due to storm waves;
  • long-term deficit of sand for upper shore face;

pit in lower shore face zone (beyond -25m depth contour);

  • no impact on nearshore wave climate;
  • no effect on nearshore littoral drift;
  • no measurable shoreline changes;
  • new extraction sand is added to nearshore morphological system (nourishment);
  • minor infill of sand in extraction pit; only during super storms;
  • trapping of mud in pits (negative ecological effect);
  • particle tracer studies show minor bed level variations (of order of 0.03 m over winter period) during storms.

Comment by MARINET:

The above facts contradict H R Wallingford reports and ‘An update of the Environmental Statement 5 Years post-dredging’ prepared for HAML in December.2005 by Marine Ecological Surveys Ltd., stating that the dredged offshore aggregate extraction pits of 3 to 5 metres deep are not filled from the surrounding sea bed. It completely disputes the claim made by the dredgers, the EA and DEFRA that Offshore Aggregate Dredging has no impact upon the coastline and puts them into disrepute.

Mike King studied his Winterton to Orford Ness Admiralty Charts, where datum are given as approximate levels of lowest astronomical tide, and found that the main licensed dredging zones shows depths of 22 to 24 metres (prior to any dredging) adjacent to South Cross Sands in the location of area 202, which decreases to 12 metres at the northern end of area 436 that joins area 202 with its northern end nearer the sand bank.

The dredged depths in these areas were from -3 metres to -5 metres prior to HAML application in 2005 to re dredge these areas, and the normal depth of their dredging operation is up to -5 metres, so in some areas in this location water depths would have been -10 metres from the above (original) chart depths after re-dredging of these areas. However, we now know that they will have infilled to some extent.

Conclusions by MARINET

The report does not tell us anything that we were not already aware of, as most has already been covered by our both our own and much earlier scientific investigations, as given under ‘Scientific Studies from around the world on the erosion resulting from offshore sand and gravel dredging’.

But what is does do is to confirm these findings and concerns and to offer recommendations from a united group of auspicious international experts, so underpinning these earlier discoveries.

The SANDPIT Report covers most all of MARINETs findings and long expressed concerns on the impact of high density long term and cumulative Offshore Aggregate Dredging on the coastline and on the marine eco-system. If the report is heeded and the recommendations are followed by the government bodies and the licensing authority, we see that many of the impacts upon our shoreline, its villages, its economy (fishing and tourism), its environment, and the seabed eco-system could be overcome.

But it needs to be pointed out that even if the measures suggested are adopted today, past dredging and that still ongoing will have a damaging effect for at least the next ten years before stability is effected.

Pat Gowen, 5th March ’08

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