Dam-Induced Hydrologic Alterations in the Rivers Feeding the Pantanal

Pedro Ely,Pierre Girard,David Kaplan,Hans M Tritico,Ibraim Fantin-Cruz

doi:10.3389/fenvs.2020.579031

Abstract

Tropical river basins have experienced dramatically increased hydropower development over the last 20 years. These alterations have the potential to cause changes in hydrologic and ecologic systems. One heavily impacted system is the Upper Paraguay River Basin, which feeds the Pantanal wetland. The Pantanal is a Ramsar Heritage site and is one of the world's largest freshwater wetlands. Over the past 20 years, the number of hydropower facilities in the Upper Paraguay River Basin has more than doubled. This paper uses the Indicators of Hydrologic Alteration (IHA) method to assess the impact of 24 of these dams on the hydrologic regime over 20 years (10 years before and 10 years after dam installation) and proposes a method to disentangle the effects of dams from other drivers of hydrologic change using undammed “control” rivers. While most of these dams are small, run-of-the-river systems, each dam significantly altered at least one of the 33 hydrologic indicators assessed. Across all studied dams, 88 of the 256 calculated indicators changed significantly, causing changes of 5–40%, compared to undammed reaches. These changes were most common in indicators that quantify the frequency and duration of high and low pulses, along with those for the rate and frequency of hydrologic changes. Importantly, the flow regime in several undammed reaches also showed significant alterations, likely due to climate and land-use changes, supporting the need for measurements in representative control systems when attributing causes to observed change. Basin-wide hydrologic changes (in both dammed and undammed rivers) have the potential to fundamentally alter the hydrology, sediment patterns, and ecosystem of the Pantanal wetland. The proposed refinement of the IHA methods reveals crucial differences between dam-induced alteration and those assigned to other drivers of change; these need to be better understood for more efficient management of current hydropower plants or the implementation of future dams.

Highlights

Growing electricity demand is a major global challenge as the need to find efficient and sustainable energy sources increases (International Energy Agency – IEA, 2019)
We identified which Indicators of Hydrologic Alteration (IHA) parameters were most affected by hydropower plant operation in the Upper Paraguay River Basin
From what precedes it is clear that many hydrological alterations in this study were dam-induced but that other drivers of change modified the regimes of the studied rivers

Summary

Introduction

Growing electricity demand is a major global challenge as the need to find efficient and sustainable energy sources increases (International Energy Agency – IEA, 2019). Hydroelectric energy is considered a source of “clean” energy (Newell et al, 2019), there are myriad environmental and social impacts related to dam operations (e.g., Fearnside, 2016; Lima et al, 2016; Latrubesse et al, 2017; Athayde et al, 2019) that must be evaluated when considering the true costs and benefits of hydropower. Country-wide, there are 639 hydropower plants, including 422 small hydroelectric power plants referred to as PCH in Brazil (defined as having production potential between 5 and 30 MW and reservoirs with a surface area smaller than 3 km2) and 217 hydroelectric facilities referred to as UHE (defined as having a capacity >30 MW in operation). In the Upper Paraguay Basin, where the Pantanal is found, there are 57 operating hydropower plants, of which 6 are UHE and 51 PCH (only 28 PCH with available data). In 2008, there were 39 operating hydropower plants in the Upper Paraguay River Basin (Girard, 2011)

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