Geomorphological mapping for route selection and road construction at lower Kihansi in Tanzania

This paper reports the use of geomorphological mapping to obtain a better understanding of the terrain for the Lower Kihansi Dam Access Road in the Udzungwa Mountains. The long-term accessibility of the road and protection of the natural resources of the area were pre-conditions for the construction of this road, which was primarily to facilitate the transportation of equipment, machinery and personnel during construction of a 54,000 m³ concrete gravity dam related to a 180-MW hydropower station. Black and white vertical aerial photographs supplemented with field mapping were used to prepare a 1 : 5,000 geomorphological map of a possible route corridor. The mapping identified areas with unfavourable ground conditions which were subsequently studied and characterized in order to select the final route. In sections where it was not possible to deviate the road from the unfavourable areas, protection and stabilization measures were considered during the design and construction phases. The road was constructed successfully and without causing damage to the environment. Geomorphological mapping proved to be a useful tool in selecting the optimum route and appropriate construction method.