For achieving the purposes of building the National Web database the following tasks were defined:
- mapping of standing water bodies such as lakes, reservoirs, fish ponds, etc.
- mapping of wetlands such as swamps, morasses, bogs, etc.
- passporting of standing water bodies and wetlands
The database answers the following requirements:
- assistance in forecasting flood hazard
- support the decision making process in risk management
- possibility for receiving the newest and actual information for the condition of water bodies (abounding in water, drained, shape and other)
Fast mapping of wetlands and standing water bodies was performed in scale range 1:10 000 to 1:25 000 over the whole territory of the Republic of Bulgaria, which is approximately 111 000 sq. km. Satellite images from SPOT with spatial resolution 5 m from years 2002 until 2006 were used for the purposes of the project. Satellite images from Landsat with spatial resolution 30 m from 2009-2010 were also used, where it was possible to observe whether the water body exists at the present moment, it has been drained temporarily or it doesn’t already exist.
Topographic maps in scale 1:25 000 were also used. When it is impossible to recognize the water body from the satellite images (it has too small area or it has been drained), but it exists on the topographic map, it is digitized on it.
In addition, for specific territories of the country VHR satellite images and orthophoto published on the website of the Ministry of Regional Development and Public Works was used to map the most important water reservoirs in scale 1:10 000.
As a result of the mapping more than 10 500 water bodies in the whole country were mapped in scale 1:25 000 (Fig.1).
Fig 1.Distribution of water bodies in Bulgaria
The water bodies on the territory of Bulgaria according to their area are divided into five classes:
≤ 0.5 ha, representing 40 % of the total number of water bodies
0.6 ha ÷ 10 ha, representing 52 % of the total number of water bodies
10.1 ha ÷ 100 ha, representing 7 % of the total number of water bodies
100.1 ÷ 1000 ha, representing 0.8 % of the total number of water bodies
≥ 1000 ha, representing 0.2 % of the total number of water bodies
In the process of comparison of the results from satellite interpretation and topographic maps it was realized that many “new” water bodies exist (they exist on satellite images but not on the topographic maps). The same was valid for the “old” water bodies (they existed on the topographic maps but not on the satellite images). This information was also included in the attributes.
The next step, after digitizing, was to be created attributive data towards graphic objects as the first received data were geographic coordinates and the area of the water body. It was inserted date of the image, from which the water body has been seen for last and the date of the image, from which the water body was mapped.
The other information is also the name of the water body, its location, watershed, some important abiotic factors, species composition, protection status and others, structured in the form of informative passport of water bodies.
With reference to the National System for Environmental Monitoring, it is important to monitor the status of wetlands, as well as the changes in their land use. The following example shows the land cover changes of a wetland, that are followed in three different years (Fig.2).
Fig.2 Historical overview of land use change in wetland “Chepintsi pit”
Ideas for future development of the project are pointed in the following directions:
- Building a National Web database to perform additional hydrologic and hydraulic analysis
•Relationship with actual data for river flows;
•Data for the distance between water bodies and settlements;
•Identification of local watersheds and their characteristics (area, % land cover, relief and others);
•Methodology for linking database with hydrometric and meteorological data – from the relevant stations;
- Completing passporting with attributes in terms of risk, disaster and accidents
- Other tasks as required by end users
Water bodies mapping with the use of satellite images is very fast method for identifying and defining water bodies location and area. What is more, this method gives most updated and actual information for the water bodies status (high water level, shape, etc.). This information is very important when the dynamics of the water bodies for a longer period of time is analyzed, as well as for the photo revision of the topographic maps. The database is multifunctional and it can be used by a wide range of specialists such as cartographers, ecologists, biologists, hydrologists, hydrogeologists and decision makers. This information system is built to provide consumers with scientific and available information, which to contribute to sustainable policy for managing water resources within the territory of Bulgaria.
Part of the database was used in SAFER FP7 project in which ReSAC is partner, to update the information sources needed for Plain Flood Risk management and Assets Mapping.
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