Hydro-physical processes at the plunge point: an analysis using satellite and in situ data

E M L M Novo,J A Lorenzzetti,J L Stech,A T Assireu,F Roland,F S Pacheco,E Alcântara

doi:10.5194/hess-15-3689-2011

E M L M Novo, J A Lorenzzetti + Show 5 more

Open Access

https://doi.org/10.5194/hess-15-3689-2011

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Abstract

Abstract. The plunge point is the main mixing point between river and epilimnetic reservoir water. Plunge point monitoring is essential for understanding the behavior of density currents and their implications for reservoir. The use of satellite imagery products from different sensors (Landsat TM band 6 thermal signatures and visible channels) for the characterization of the river-reservoir transition zone is presented in this study. It is demonstrated the feasibility of using Landsat TM band imagery to discern the subsurface river plumes and the plunge point. The spatial variability of the plunge point evident in the hydrologic data illustrates the advantages of synoptic satellite measurements over in situ point measurements alone to detect the river-reservoir transition zone. During the dry season, when the river-reservoir water temperature differences vanish and the river circulation is characterized by interflow-overflow, the river water inserts into the upper layers of the reservoir, affecting water quality. The results indicate a good agreement between hydrologic and satellite data and that the joint use of thermal and visible channel data for the operational monitoring of a plunge point is feasible. The deduced information about the density current from this study could potentially be assimilated into numerical models and hence be of significant interest for environmental and climatological research.

Highlights

According to the report published by the International Committee of Large Dams (ICOLD; www.icold-cigb.net) in 2000, over 40 000 large dams exist in the world, with a total storage capacity of 7000 billion m3
The resulting increases in the inflow have a strong effect on the thermal structure of the reservoir during the wet season.FIignutrhee2: Daily means of air temperature, wind speed and precipitation and dry season the long-term decreasing trend in the shortth-ewdavaiely meaFnigs.o2f
The air temperatures declined by approximately 6 ◦C during these events, and the daily average wind speed reached 6 m s−1

Summary

Introduction

According to the report published by the International Committee of Large Dams (ICOLD; www.icold-cigb.net) in 2000, over 40 000 large dams exist in the world, with a total storage capacity of 7000 billion m3. Changes due dams can include increased depth, changes in temperature, the possible development of density stratification, the retention of nitrate and phosphate, the growth of plankton and algae, contaminant trends in sediment, changes in the aquatic ecosystem from lotic to lentic, and the release of carbon-based greenhouse gases (Baxter, 1997; Poff and Hart, 2002; Ramos et al, 2006). Because the density of the river water reaching a reservoir usually differs from the density of the water at the reservoir surface, inflows enter and move through the reservoir as density currents (Ford, 1990). Temperature, total dissolved solids, and suspended solids can cause density differences. Depending on the density difference between the inflows and ambient waters, the density currents in a reservoir can flow into the downstream area as overflow, underflow, or interflow types (Martin and McCutheon, 1999)

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