Jeddah is using DTM to safeguard the c ity against the occasional winter thunderstorms
Jeddah is a major urban centre in the Kingdom of Saudi Arabia and is the second largest city in the country after its capital Riyadh. While the city receives sparse rainfall like most other areas in the region, it is not uncommon to have heavy thunderstorms in winter. This creates the need for a detailed flood risk analysis of the region.
In 2010, the Jeddah Development and Urban Regeneration Company (JDURC) commissioned a project to build a detailed digital terrain model (DTM) to support flood risk analysis in the region and study the subsequent design of dams protecting the city along with temporary and permanent storm water drainage channels.
The project was subsequently awarded to Vision ME. In December 2010, Vision ME commenced the acquisition of high-resolution digital aerial photography and LiDAR data for a total area of 6,400 sq km, covering the entire Province of Jeddah. Aerial photography was acquired using a Vexcel UCXp digital aerial survey camera supported with GPS base stations, the Jeddah CORS network and PPP processing to create an extremely accurate dataset. LiDAR data was acquired with the help of over 120 hours of flight at a density of two points per sq metre using Leica ALS 50 Mk II equipment. The final output was a dataset that could be integrated into both GIS and CAD systems to support all design activities. All data went through a strict quality control and acceptance process to ensure that the project accuracy was maintained.
Quality checks demonstrated that accuracies better than 10 cm in height were achieved, with horizontal accuracies better than 20 cm. The final delivery included a re-processed Pictometry oblique image library. This data was acquired during 2007 and benefitted with an accuracy improvement with the inclusion of the new DTM data.
The final project deliverables included:
- 10 cm resolution seamless digital orthophoto at 16-bit
- DTM at 1 metre grid intervals throughout the project area
- Contours at 20 cm and 1 metre vertical intervals
- Building outlines
The project was completed during the latter half of 2011. The digital terrain model created with the help of data generated by Vision ME will help in building a base map of the city that will be used by the GIS centre for a detailed GIS analysis. It will also form a base for carrying out several other projects in the region. It will facilitate quick response during emergency situations and provide early warning for an impending disaster. Besides, the data will also be used for future planning and re-planning of existing slums in the city.