Reservoirs Location using weight coefficients and distances.
By Ioannou Konstantinos, MSc, PhD F. Informatics
For the calculation of the optimal locations for the water reservoirs installation, initially we conduct a multicriteria analysis, using a special software. The criteria used are the following:
1. Distance from roads
2. Distance from stream network
3. Land Uses
These criteria are imported on the specialized software (Picture 1) kai we set the proper goal, which for our case is the calculation of the optimal reservoir locations. The goal is set to 1.0.
Picture 1.The criteria
Afterwards the criteria are evaluated with each other using the Saaty scale. According to this scale each criterion is compared with another (pairwise comparison) and a number is given to this comparison based on the level of significance of the comparison. The number one is given to a comparison of two equal importance criteria, and the number 9 is given to criteria which is strongly more significant than the other (Picture 2).
Picture 2.The criteria comparison
When all the comparisons are finished, we ask from the application to record the judgements and calculate the weight coefficients. For out example the weight coefficients are calculated and presented in the following table.
Table 1. Weight coefficients
The previous table, clearly depicts a well known fact, the most important criteria for the water reservoir location are in descending order
1. Roads Distance
2. Stream Distance
6. Land Uses
This result was expected, because we will need the fire department vehicles to be able to access the reservoirs, and this will be one of the major constraints. Thus we must allocate the positions near to roads for them to be accessible fast, near to streams for the reservoirs to be filled with minimum amount of technical works, easily accessible by trucks in area without steep slopes, located in southern aspects which are considered drier from all other aspects. Finally, the reservoir location will be affected by land uses, meaning that we will not propose a water reservoir in the middle of a village or a lake.
Each of the calculated criteria, contains a subset of parameters which affect the criterion, these parameters are considered internal and must be set in order to properly create the final map.
1. Distance to Roads
The first step was the surveying of the entire road network of the area using GIS. The network was then characterized, based on the road type, in two major categories, national roads and forest network. The forest network was further divided in two categories, A and B, based on the handbooks provided by the Greek Forest Service. In the following picture we present the national road network of the Menoikio mountain in red color, the type A forest road in green and finally the type B forest roads in light blue.
Picture 3.Menoikio Road Network
Then we created a weighted map of the road network based on the fact that it was preferable to create a reservoir closer to the existing road network and we divided the existing map in three categories using the Distance tool of Spatial Analyst.
Picture 4 The weighted Road Network
In the previous map, locations with green colour are the most suitable for the reservoirs, locations in purple colour are less suitable and finally locations in brown colour are not suitable.
2. Stream Distance
After the completion of the surveying of the stream network, we created a map, of the area with the stream network, and based on the previous methodology we used the distance tool to calculate distances from the stream, this each pixel on the derivative map contain information regarding its distance from the stream network. Using the same principle as before we created three levels of distance.
Picture 5.The weighted Stream Network
The term accessibility is used to describe whereas the area is accessible by vehicles. Fire Service vehicles have limited ability to access steep slopes, especially when they are loaded with water and personnel. For this reason, we used the contours map in order to determine areas with steep slopes, under the assumption that road slopes greater than 10% are inaccessible from fire service vehicles. The resulting map is shown in picture 6.
Picture 6. The weighted Accessibility map
The previous picture represents the map with the areas that are accessible to vehicle. The green areas depict the most accessible area (0-5%), the yellow, the areas with less accessibility (5-10%) and finally, the white areas, represent areas that are inaccessible from vehicles.
The next map represents the ability to create a technical structure, like a reservoir, with the optimal cost, and based on the fact that it will not need special construction techniques that will damage the Natura 2000 site and will be cost inefficient. For this reasonwe created a map divided in three categories, one for slopes of 0-10% (most suitable areas for reservoirs), one with slopes of 10-20% (less suitable areas) and finally one for slopes of 20% and more which represents areas with less suitability, meaning that reservoirs in these areas will require extensive technical works which will damage the environment and will be costly. The slope map will be similar to
Picture 7.The weighted slope map
The aspect map derives from the fact that southern aspects are drier on the Northern Hemisphere. This is the main reason that makes southern slope more fire prone than the others. Based on the Digital Elevation Model of the Region, we created the aspect map of the study area, having in mind that aspects with greater fire risk will be more suitable for reservoirs. Following that we reclassified the initial aspect map, in three categories, with south, south east and south west aspects, presenting the most suitable locations for water reservoirs. The resulting map is presented in Picture 8. Areas with greater fire risk are depicted in purple, with less fire danger are depicted in yellow and green and at last, areas with the list fire danger are depicted in brown.
Picture 8. The weighted aspect map
6. Land Uses
The last map used will be the one presenting the area land uses. This map was based on the results of the CORINE 2000 land use program, and contains the land uses of the area divided in the following categories.
· Discontinuous Urban Fabric
· Mineral Extraction Sites
· Non Irrigated Land
· Olive Groves
· Agricultural Land
· Broad Leaved Forest
· Coniferous Forest
· Mixed Forest
· Sclerophyllous Vegetation
The aforementioned land uses types do not represent the same fire danger, thus we reclassified the map using the fire risk map and the land use types that are more prone to fire like the the coniferous forests.
Picture 9.The Fire risk map (courtesy of Mitsopoulos, I)
The resulting map based on the Land Uses Map and the Fire risk Map is presented in picture 10. In this map, areas with greater fire risk, and thus most suitable for water reservoirs are presented in purple.
Picture 10.The weighted land use map
7. Distance from Vehicles.
Given the fact that the fire departments that are closer to the study area are located in Drama, Serres and the detachment of Nevrokopi the water reservoirs must be located closer to the entry points from these locations. Picture 11 depicts the entry points from the three fire departments. The entry points are presented as green triangles, and the National Road Network that will be used in order to access the entire area is presented in red.
Picture 11.The entry points.
8. Optimal Reservoirs Locations
By Ioannou Konstantinos PhD and Kaziolas Dimitrios PhD
The map presented in the previous pages will be used in combination with the calculated weight coefficients using the following math formula.
Where RD is Road Distance, SD is Stream Distance, Acc is Accessibility, Sl is slope, A is aspect and LU is land use. The application of the previous formula to the maps produces the result presented in picture 12. In this picture we present the result of the calculation where whiter areas represent areas that are more suitable for the reservoirs. The three green triangles, represent the entry point of the vehicles.
Picture 12 The reservoirs proposed locations (white)
After visiting the proposed locations, and having in mind that the locations must be easily and quickly accessible and must be build with the minimum cost, we selected the following areas were we must create the reservoirs.
Picture 13, presents with green circles the proposed locations of the water reservoirs, along with the present national road network in red, forest road network in green, and stream network in blue.
Picture 13.The proposed reservoir locations.
Finally, the optimal routes where found. First we determined the entry point for the fire fighting vehicles. The meaning of the entry points is the determination of the junctions which pass when the approach the study area (Green triangles in Picture 14). Afterwards we created a cost surface based on the fact that the vehicles cannot access roads with slope greater than 10%. Then by applying the shortest path methodology we determined the optimal routes for accessing the proposed reservoir locations (picture 14)
Picture 14. Optimal Routes