GIS sediment assignment

Authors: Cosmin Parlog,Floris van den Hurk

Education: Water Management

Course: CU08656 -Water system analysis

Lecturer: Alco Nijssen

Date: 28.05.2013

Place: Vlissingen, the Netherlands

Contents1. Introduction.......................................................................................................................................1

2. Approach and Methodology..............................................................................................................2

3. Results...............................................................................................................................................4

4. Discussion & Conclusion....................................................................................................................9

1. Introduction

The Western Scheldt is an estuary located in the most southern part of the Dutch coast. Since the

harbour of Antwerp is connected to this estuary, a lot of shipping activities take place. For this

reason the main channel is kept intact with dredging activities. The dredging process in the Western

Scheldt is a continuous process in which a yearly amount of 7 million cubic meter of sand are

dredged. All the dredged material has to be dumped and because the current dumping sites are full,

there is the need to find new relocation sites in the Western Scheldt, where environmental impact is

the lowest. The aim of this report is to find new suitable dumping locations for the dredged

sediments, by preforming a spatial analysis with the help of GIS.

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2. Approach and Methodology

To start with, a cartographic model was made, which is a graphic representation of data and the

analytical procedures used in this assignment. The analytical procedures, in this case, are the

functions reclass and overlay that were used in GIS to create a map that portrays desired. Figure 1

show the cartographic model. The final product is a map showing the most suitable dumping

locations. To be able to assess which suitable dumping locations are available seven preconditions

were chosen, to which the final map must comply. These requirements are listed below:

1. Sediments should not be dumped at locations with high species richness;

2. Dumping locations shouldn’t overlay fishing grounds;

3. No high biomass should be present at the new dumping sites;

4. Former dumping areas must be avoided;

5. Dumping sediments may not interfere with dredging activities;

6. Sediments must stay in the water body;

7. To avoid erosion the velocity of the water at the dumping locations must be as low as

possible;

For each of these requirements a corresponding Boolean map was made, using the reclass function

in GIS. Each Boolean map contains the values one and zero. The value one indicates a positive

possibility to dump sediments, whereas zero indicates that no dumping activities should take place.

Consequently the seven Boolean maps were overlaid to create the map BestDumpOK, in which the

positive dumping locations meeting all seven requirements are shown.

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3. Results

The map species is chosen to evaluate and analyse the species richness. The map showed six degrees

of species richness present in the estuary. In the Boolean map speciesOK, made from the map

species, the acceptable degrees of species richness have the value one for very poor, poor and quite

poor (see figure 2).

Figure 1 Topographic result of reclassifying the map species.

The map shrimp shows current locations where fishing activities for shrimp take place. In the

Boolean map shrimpOK, made from the map shrimp, the value one is given to locations where there

are no fishing activities.(see figure 3.)

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Figure 2 Topographic result of reclassifying the map shrimp.

The map biomass portrayed six degrees of biomass concentration. In the Boolean map biomassOK,

made from the map biomass, the acceptable degrees of biomass have the value one for very low,

low and quite low biomass concentration.(see figure 4)

Figure 3 Topographic result of reclassifying the map biomass.

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The map dumping areas shows the location of current dumping sites. In the Boolean map dumping

areasok , made from the map dumping areas, the value one is given to locations where there are no

current dumping sites.(see figure 5)

Figure 4 Topographic result of reclassifying the map dumpingareas.

The map dredging displays the current locations where dredging activities are taking place. In the

Boolean map dredginOK, made from the map dredging, the value one is assigned to the values

consistent with no dredging areas(see figure 6).

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Figure 5 Topographic result of reclassifying the map dredging.

The map Scheldt displays the boundary of the Scheldt estuary. In the Boolean map Scheldeok, which

was made from Scheldt, the value one is given to the data Water (see figure 7).

Figure 6 Topographic result of reclassifying the map schelde

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The map velocity illustrates the values of the velocity of the water in the estuary. In the Boolean map

velocityok, made from the velocity map, the value one is given for velocities smaller than 0.5 meter

per second (see figure 8).

Figure 8 Topographic result of reclassifying the map schelde

All the Boolean maps are put together in order to create the BestdumpOK map. This map displays

the best suitable dumping sites with the colour cream. (see figure 9)

Figure 9Topographic result of reclassifying the map schelde

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4. Discussion & Conclusion

The final area suitable for the sediment unloading is 281.01 hectare. Taking in account that the

average depth of the Western Scheldt is 6 meter a rough estimate of the total volume of available in

these areas is 16860734.82 meter cube. For a more accurate calculation each specific area can be

multiplied by its depth.

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