HERA – Hydropower and Environmental Resource Assessment is a computational model that estimates the feasible hydropower potential of a watershed and studies the scheme (plant site selection) that best exploits this potential. HERA uses a mathematical model to maximize the "economic benefit", given by the difference between revenues from the electricity produced in the projects and total costs (project direct costs or indirect costs related to the possible flooding of urban areas, highways, railroads, etc.).
In addition to the selection of the most advantageous sites, HERA estimates the project designs (gross head and installed capacity) through an economic evaluation. To this end, HERA has a module responsible for the budgeting project alternatives at each site. This module uses a unit costs database and quantitative measurements (concrete and excavation volumes, for instance) which are automatically computed.
The time series of monthly inflow at each project site can be approximated by a regionalization of streamflows measured in neighboring gauging stations. In Brazil, the HidroWeb database from the National Water Agency may be used. Topographic data can be generated from an aerophotogrametric study supported by field surveys or obtained with less precision from public databases, such as ASTER GDEM and STRM, from NASA.
It is important to mention that HERA does not replace the complete “inventory study” (watershed planning) required for approval by ANEEL. The purpose of the tool is to provide a low-cost initial assessment of the hydroelectric potential that is economically and environmentally viable. HERA is a decision support tool that indicates whether the selected region offers favorable characteristics that may be scrutinized in later studies or an indication for halting these. In this latter case, the value of HERA lies in the avoided cost, as complete watershed inventory studies cost a few million dollars.