Planning for Coastal Development along the Coast of Karachi

As cultures worldwide draw increasing attention to the relationship between environmental quality and economic development, preserving the visual quality of coastal landscapes is growing in importance. The concerns range from a purely aesthetic desire for preserving the beauty of the coastal landscape to those over the potential ecological impacts of alterations of the landscape. Planners of coastal landscapes, in particular, considering such concerns must integrate different values including the seascape's potential for attracting a sustainable tourist business, expanding residential growth, or pursuing other forms of economic development. The visual priorities placed on a coastal landscape are indeed diverse.

This exercise addresses the issue of sea influence upon the planning and development of coastal landscapes. The development potential of any coastal area depends upon the availability of clear views and access to the sea. It also depends on factors such as the distance from the shore, and the slope and aspect of the land. A detailed analysis of such factors is important for the effective and balanced management of the coastal zone, and a GIS is one tool capable of enhancing the analysis.

The exercise relies on a digital elevation model of a part of the coastal area of Karachi.

a) Open ArcMap and Set your Working folder to that which holds the data for this exercise

Since commercial and residential development is most likely to occur in coastal areas with a view of the ocean, the first step in this exercise is to identify such areas.

Part 1: Viewshed Analysis

For this analysis, VIEWSHED tool from Spatial Analyst will be used, which determines all the surfaces visible from a selected point or set of points. In order to run VIEWSHED, a DEM of the study area and a viewpoint from which the view is determined. In our case, the surface is the digital elevation model. We do not have a viewpoint and need to create one.

Preparing the Data

1. DEM (Available in the folder)2. Viewpoint (Arccatalogue – working folder- create new shapefile)

To digitize, move the cursor to some point in the ocean (not too far from the shore) and press the left mouse button. The feature is drawn on the screen as it is digitized (you can draw multiple points).

Creating the Viewshed

To open Viewshed tool Go to ArcToolBox

toolboxes\system toolboxes\3d analyst tools.tbx\visibility\Viewshed

Or

Just search Viewshed in the Search window

One way to isolate this view would be to create a mask where land = 1 and sea = NoData and multiply this mask with the Viewshed image.

Part 2: Determining Panoramic Views

The development of the coastal landscape will most likely take place in those areas of the land that offer panoramic views of the ocean rather than a narrow view of the ocean. To find which areas offer panoramic views of the ocean, we adopt the following procedure. First, we create a viewshed image for a point located in the lower left hand corner of DEM and a point located in the lower right hand corner of the DEM. We then mask out the areas that are in the ocean. These land areas can be thought of as offering panoramic views of the ocean because the two viewpoints visualized from these areas are located wide apart in the ocean. The surface image for creating the viewshed will remain PANVS.

Go to search window and write reclassify

To extract the viewshed overland use the masked land from shore line to upto 1000 meters toward land.

To extract the land part first use Con tool (spatial analyst) from search window

Save output as ocean_con

Check the values from ocean if there are negatives values on land reclassify the raster to remove these values.

Save output as ocean_con

To limit our analysis from shoreline to 1000 meter toward land, we need a distance raster. It is necessary to have a feature image or a "target" which defines from where landward distance will be measured. Since we want distance to be measured from the shore, the ocean will be the target from which calculations are made. To create distance raster go to search window and search path distance.

Save output as Distance

To extract the area from shore line to 1000 meters reclass the distance raster.

Save output as Dist_rec

Convert raster Dist_rec into polygon and use it to clip PANVS (use this polygon to clip other rasters Aspect and slope in suitability analysis)

Part 3: Suitability Analysis

We have determined which areas of the coastal land have a panoramic view of the ocean. We now turn to an analysis of the other variables that may influence the development of the coastal landscape. In addition to the view of the ocean, our ability to enjoy the ocean depends upon the distance from the shore, the slope of the land, and the aspect (the angle at which a potential viewing area faces the ocean).

In suitability analysis, different images are combined to produce a suitability map showing areas that are potentially useful for certain types of activities. In our case, suitability analysis can be used for predicting the development of the coastal landscape. In this example, we have four criteria for where development may occur:

1)only land areas with panoramic views of the ocean2)with a north facing aspect3)within close distance to the shore4)with low slope

Creating Images of Development Criteria

1. Slope Go to search window and write slope

Save the output image as SLOPE

Go to search window and write reclassify

For slope, reclassify the image as follows: 1 = 0 - 25 degrees; 2 = > 25 degrees.

Save the reclassified image SLOPE_Rec.

2. Aspect Go to search window and write Aspect

Save the output image as Aspect

We limit the aspect image to contain only land surfaces facing North. It now contains aspects that range

from 0 to 360.

Go to search window and write reclassify

For Aspect, reclassify the image as follows: 1 = 0 - 45; 2 = 45 - 315; 3 = 315 – 360

Save the reclassified image Aspect_Rec.

Create Suitability MapNow we have all the three rasters of Viewshed, aspect and slope. Use raster calculator to sum all

the rasters. The highest values of the sum-raster shows that all the three criterion satisfied at that

particular location.