Assessing Alternative Large-Scale Reservoir Operation Conditions to Increase Water Security under Changing Hydrology: Development of HEC-ResSim Reservoir Simulation Model and HEC-RAS River Analysis System Model of the Grande River System

Código

I-EBHE0175

Autores

William Doan, John Hazelton, ALAN VAZ LOPES, Antônio Augusto Borges de Lima, MARCIO TAVARES NOBREGA, Joaquim Guedes Correa Gondim Filho

Tema

WG 2.6: Water systems analysis for integrated planning & management

Resumo

The Grande River System in south-central Brazil was severely impacted by a hydro energetic crisis in 2021 caused by significant accumulated rainfall deficits, resulting in excessive reservoir depletion and impacts in multiple water uses such as navigation and recreation. Alternative reservoir operation rules can be applied to conserve water during drought periods and reduce the risk of water shortage. However, risks and impacts resulted from alternative operations are felt differently by each water use depending on their water demand characteristics and degree of dependency of the water system. Moreover, changing hydrologic conditions might add uncertainties that still challenges the process of formulation and assessment of new operational rules. To tackle those challenges considering multiple water uses and changing hydrologic conditions, an HEC-ResSim reservoir simulation model and HEC-RAS river analysis system model were developed for the Grande River System in order to explore potential alternative operational scenarios of the reservoirs within the system, including downstream impacts on the reservoirs on the Parana River. The analysis takes an integrated water resources management approach as it tries to maximize all potential benefits associated with operations of the reservoir system, including hydropower generation, flood risk management, navigation, recreation, and environmental, under different hydrologic scenarios. This effort was developed and performed to quantify the hydrologic, water management, hydraulic and economic effects associated with potential alternative reservoir operational rule designed to reduce the risk of reservoir depletion during drought periods and therefore increase water security for multiple water uses. HEC-ResSim is a USACE, publicly available modeling software program used to assist in evaluating existing and proposed reservoirs, reservoir operations, and to assist in assessing or quantifying impacts of various reservoir operational scenarios. HEC-ResSim utilizes river alignments, river routing reaches, physical reservoir properties, reservoir operational zones, guide curves, and operational rules to simulate real-life operations of a reservoir or system of reservoirs. The period from 2002 to 2023 was used to calibrate the model to simulate actual real-life baseline operations of the reservoirs. Then, alternative scenarios of reservoir operations were then modelled in HEC-ResSim for the same time period using daily time steps, under different hydrologic conditions. From these results, statistical parameters of hydropower production, reservoir pool durations, release durations, and reservoir release frequencies using the HEC-SSP Statistical Software Package were developed for baseline and alternative scenarios. Additionally, two-dimensional HEC-RAS flood inundation models were developed downstream of reservoirs at critical locations to determine various recurrence level flood inundations extents resulting from reservoir releases and tributary inflows. These statistical parameters and flooding frequencies can be used to determine benefits and adverse impacts on hydropower generation, navigation, recreational benefits associated with each operational alternative. Results indicate that new operational rules that associate maximum reservoir releases to reservoir storage can significantly reduce the risk of reservoir depletion during extreme drought periods. As a consequence, each water use sector enjoys specific benefits such as reduction in the risk and duration of navigation interruptions, increase in duration of adequate water levels for recreation and increase in water availability for hydropower generation.