The Senegal River, which flows west from Mali to form the border between Senegal and Mauritania before it empties, 1,800 kilometres downstream, into the Atlantic, was about to undergo its first bathymetric survey when it was discovered that an essential prerequisite – a digital map of the river – did not exist. Instead of stopping the three-nation project dead in its tracks and creating a costly overrun, surveyors kept the project on schedule using a small, handheld GPS navigation and GIS data collection system that happened to be on-scene.

Hydrographic department teams from Senegal and Mauritania were aboard two survey-vessels to begin a preliminary bathymetric survey of the entire length of the river when the map oversight was discovered. Fortunately, a Thales representative onboard to train operators of some newly installed Thales Aquarius positioning units happened to have with him a MobileMapper Pro with built-in WAAS/EGNOS-receiver and post-processing differential correction software. After just an hour’s training, a crew was aboard a Zodiac inflatable dinghy recording the outline of the riverbanks with the handheld GPS. This initial effort proved so successful, so quickly, three additional handheld GPS receivers were immediately ordered and the entire survey project proceeded up-river after only minimal delay.

The map of the river was digitally drawn one day at a time by keeping two Zodiac crews armed with handheld GPS collecting data along the riverbanks one day ahead of the survey vessels. Each day at day’s end the Zodiac crews would download their data into the acquisition and preparation software aboard the survey vessels for use the next day. In this way, approximately 80km of the 1,800-km river was mapped and surveyed each day. It took less than a month to complete the entire project.

Senegal River Project
The hydrographic departments of Dakar, Senegal; Nouakchott, Mauritania and Mali are jointly undertaking efforts to measure and safeguard water level and flow and the condition of the Senegal riverbanks. They also plan to establish demarcation of the navigable channel on this most important water supply, the only commercial route through the desert regions of the three countries.

Acknowledgements
Thanks are due to the Hydrographic Departments of Dakar, Senegal; Nouakchott, Mauritania and Mali, and to Port Autonome de Bordeaux for contributing to the writing of the article. Port Autonome de Bordeaux authorities are working in co-operation with the Senegal Port authorities to provide them with technical assistance.