The role of a dam in a water management system in Italy: physical and economic implications

On 4(th) November 1966 a flood hit the city of Florence, with a water discharge from Arno River of 4200 m(3)/s causing death and destruction. To safeguard Florence against any such future events, the Bilancino dam was built along the Sieve River, the main right tributary of the Arno River. The dam is also an important element for the water management of the Florence area. The artificial basin is 5 km(2) wide and represents a water reservoir of 8.4x10(7) m(3). The paper presents the results of the emergy evaluation of the Bilancino's artificial basin and its role. The emergy evaluation is an environmental accounting method that converts all different inputs, inflows of energy and matter into a system or a production process, to a common denominator, the equivalent solar energy. The emergy represents the quantity of solar energy that was used, directly or indirectly, to obtain a good or service. In other words, emergy accounting enables to "memorize" all the energy that was necessary in the past to obtain a flow or a product that is available today. The environmental costs of the Bilancino's dam, which creates the basin, as well as the economic benefits of its presence are evaluated from an emergy point of view. In order to calculate the emergy of the dam, the resource flows constituting it have been considered: materials used to build the dam (rockfill diabase, rockfill limestone, gravel, sandstone and clay) and construction and annual management costs. Environmental costs like sediment loss and the loss of organic matter (land) have also been taken into consideration. The emergy investment for the construction and maintenance of the dam is finally compared with the emergy estimate of a future incidental flooding.