Modelizar la SCVLF dicotomizada a partir de sus valores medios

Van den Branden Reinhilde*1, De Schepper Gregory1, Naudts Lieven1

*

Presenting author: [email protected] 1

Royal Belgian Institute of Natural Sciences, OD Nature, Measuring Services Ostend, 3de en 23ste Lnieregimentsplein, 8400 Ostend, Belgium

Sand extraction on the Belgian part of the North Sea started in 1976. But it is only since 1996 (due to the Royal Decrees of 1996 and later: koninklijke besluiten betreffende de exploratie- en exploitatievoorwaarden verbonden aan de concessiebesluiten) Electronic Monitoring Systems (EMS) are used to record and control the sand and gravel extraction activities on the Belgian part of the North Sea. Over the years, slight adaptations were made in the legislation and agreements concerning EMS obligations resulting in full EMS data records (from extractions performed by the private sector) available since June 2002. In addition of OD Nature’s responsibility to manage and process the EMS data (agreement with FPS Economy, Continental Shelf Service), data was also processed and reported (from various logging systems) from extractions with trailing suction hopper dredgers (TSHD) without EMS in the framework of the construction of submarine pipelines in 1997 (Interconnector and NorFra) and of coastal protection (beach nourishments) and other maritime works (Flemish Region, Coastal Division and Division Maritime Access) in 2004 and 2005. Afterwards, activities on the license of the Flemish Region are also monitored by the EMS.

The obligation to install an EMS on the TSHD that meets the technical specifications is regulated as a condition for the concession. The EMS automatically records among others the following parameters: identification of the vessel, the code of concessionary, the date, the time, the geographical position, the speed, the status of dredging pump(s) and the dredging activity. All necessary sensors are installed to enable the recordings of the parameters above-mentioned. On the one hand, this closed and sealed system (and its recorded and processed data) allows to verify whether other conditions of the concession are respected: permitted areas, minimum average speed during extraction and, if necessary, the to be respected distance between multiple extraction vessels. The processed data gives also an indication for the maximum volume that has been exploited. On the other hand, the recorded and processed EMS data is one of the tools for the continuous monitoring of sand and gravel activities. This in addition to the data derived from the registers and from the regular bathymetric, hydrodynamic and sediment transport surveys. The presence of an EMS on the dredging vessels is also controlled by the Aerial surveillance team of RBINS-OD Nature-MUMM (SURV), which reports on the observed dredging vessels and their extraction activities.

Since 2014, new EMS-systems are operational. The main reason for the renewal was the ability to follow up more frequently the proper operation of the recording device and the recorded data (via telemetry) (schematic view, see Figure 1). Another change is the entry by the crew of the parameter ‘actually extracted volume’ after every trip. During the pilot project a system that complies with the new specifications was placed parallel to a former EMS for detailed comparison and evaluation purposes. The final results of the pilot were presented to the Advisory Committee on June 25, 2013 followed by a circular of Continental Shelf Service to the concessionaires on August 22, 2013. Herewith, all concessionaires were informed of the revised technical specifications and guidelines for the EMS which they had to fulfill by the beginning of 2014. The new systems permit short-term data availability, which allows a better monitoring of the extraction activities as well as taking faster appropriate policy

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measures (for example closure or opening of certain parts of the sand and gravel extraction zones) when needed.

The EMS data records (both from the old and new systems) also allow for an estimation of sand extraction intensity (extracted volume of trailing suction hopper dredger per timeframe by using the declared load (new EMS) or the known fixed loading capacity (old EMS)). This enables the final data table to be used to evaluate the extracted volume on any surface and for any timeframe as well as making grids of extracted volumes per year.

The new EMS truly fulfills the expectations, seen the following characteristics: low cost, easy to install and to maintain, reliable performance;

data falsifications is almost impossible;

the compatibility with the demands of the ICES WGEXT working group and OSPAR makes the correct reporting of the analyzed electronic monitoring data (geospatial data on extraction locations in the form of shape files) straightforward.

The only disadvantage of the current system is that extracted volumes (per timeframe) are estimations (as the EMS is not equipped with sensors to record the load) but practice shows this approach is more than satisfactory.

GPS

Sealed EMS Installation

Dredging pump(s) Activity of the pump

EMS Date Time Position Speed Display + Keyboard Travelnumber Concession code Activity Alarm OD Nature Captain Read Report Feedback Approval test

Seal & Unseal

Modem & SIM Mobile network

Shore station OD Nature

Memory card

Extracted volume Activity override

Figure 1: Schematic overview of the EMS as in use since early 2014 (EMS 2.0), the interaction with the system and the changes relative to EMS 1.0 are marked in yellow.

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Master Plan Coastal Safety: work in progress

Van Quickelborne Elias*1

*Presenting author: [email protected] 1

MDK, Afdeling Kust, Vrijhavenstraat 3, 8400 Oostende, Belgium

Already over three years ago, on June 10th 2011, the Flemish government approved its Master Plan Coastal Safety. It was a milestone that led to numerous investments scattered over the entire coastal stretch. The Coastal division came up with solutions and alternatives to reduce the flood risk and to protect us against a 1.000 year storm event up to 2050, taking into account current and predicted hydraulic conditions and thus also climate change. The plan combined so called hard and soft measures to improve the safety level along our coast while the environmental impacts, social and cost benefits and – above all – consultations with other stakeholders, were anything but overlooked.

Besides hard measures in and around residential areas and harbours, nourishments in particular are still the primary action taken by the Coastal division to strengthen the sandy part of the coastline. Existing extraction zones were not appropriate and could not cope with the increasing demand of such a huge amount of sediments with the most appropriate characteristics. Following a preliminary investigation in the area of the Hinder Banks, i.e. a zone with massive tidal sandbanks known for their coarse grained surface sediments and based on the integration of seismic and vibrocore data, 4 new extraction areas were delimited allowing public and private parties to extract as from 2011. This indeed significantly broadened the options for the government regarding grain size availability and hopper sailing distance.

The true start of the Master Plan Coastal Safety took place in October 2011 in the community of Koksijde with a small beach nourishment and subsequently projects in De Panne and a medium size nourishment in Wenduine. Wenduine 2012 was also the first nourishment with sand originated from the Hinder banks. It also confirmed the previously obtained scientific outcome and the results of the field research with respect to the extracted sediment characteristics.

However it was until autumn 2013 and spring 2014 when the extraction volume for beach nourishments truly peaked. Westende, Middelkerke, Raversijde, Mariakerke, Oostende, Bredene, Wenduine, Blankenberge and Knokke-Heist all were tackled partly accelerated by a severe storm event December 5th & 6th 2013.

That storm was in the first place a test for the readiness of the public authorities. With historic water- levels and luckily changing wind and storm conditions, the damage to the primary sea defence i.e. the beach and dunes was notable and in need of fast repairs though the nourishment works from the past have proved that they were absolutely necessary to withstand the storm.

Between September 2013 and June 2014 a total of over 4 Million m³ sand (excl. extractions through beneficial use of sediments f.i. nourishment works combined with dredging works in non-controlled areas) was extracted, putting the dredging industry in Flanders in higher gear.

Sustainability of those replenishments could indeed be questioned. Maintenance is however inherent to nourishments and all kinds of soft protection measures to protect us against the quirks of nature. The Coastal Division is therefore exploring the usefulness of for instance foreshore nourishments. Early results of a pilot foreshore nourishment in Mariakerke show that those can be particularly cost- effective due to beneficial use of sediments and higher dredging efficiency.

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Also, there will be strived for a sustainable management of the exploitation zones through spreading or rotation with an accompanying and extensive monitoring program on both the extraction areas and the beaches.

Meanwhile cranes and bulls are still shaping our beaches, dunes, seawalls and harbours while other realized projects along our coastline are already part of the image of the coast today and one can only see the past on dated aerial images.

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Aggregate extraction versus archaeological heritage: how to reach