Frederico Fábio Mauad

Hydropower reservoir sediment and water quality assessment

Purpose Finer sediment particles (silt and clay) transported by rivers carry the major part of nutrient loads by absorption; thus, sediment settling can remove nutrients from the water column. The purpose of this paper is to analyze the relation between reservoir sedimentation and water quality by assessing the reservoir sedimentation process and the sediments’ characteristics. Design/methodology/approach Bathymetric surveys from 2004 to 2014 were analyzed to assess the sedimentation process. Core samples provided information on a layer-by-layer basis of the sediment deposits, and water samples near the surface and near the bottom provided information on sediment concentration, and adsorbed and dissolved nutrients. Findings The upstream region of a reservoir is already silted. From 2004 to 2014, the delta evoluted approximately 500 m downstream and the deposits were mainly composed of clay. An area of approximately 1,000 m between the delta and the dam should still be able to continue allowing sediment deposition in the coming years. Most of the nutrients were absorbed into the sediment particles, except for the nitrogen measured in the dry season. Research limitations/implications Although analyses of the full cycle of the nutrients were not carried out, the constant sediment trapping of finer sediments and the high rate of absorbed nutrients in the suspended sediment support the hypothesis that the reservoir has removed nutrients from aqueous media by adsorption into sediments. Practical implications In the studied case, reservoir sedimentation has led to better water quality downstream. Originality/value It is shown in this study that reservoir sedimentation may have positive effects on river water quality.

Influence of Sedimentation on Hydroelectric Power Generation: Case Study of a Brazilian Reservoir

AbstractMany reservoirs of hydroelectric power plants currently operate with outdated data due to the continuous sedimentation process. This fact demands management and operation policies for these reservoirs based on data different from those actually found. This paper presents a case study of Tres Irmaos Reservoir (in Sao Paulo state, Brazil), where a bathymetric survey was conducted in 2008. From the comparison of the data obtained in the survey and data from 1975 (provided by the power supplier), it was possible to estimate the reservoir losses of total, active, and inactive capacities. From the observation of changes in the reservoir’s operational data, a simulation of the power plant and the reservoir operation was conducted using MODSIM/AcquaNet software to analyze the interference of the reservoir sedimentation with the generation of electricity.

Density currents at steady regime

This work brings as its main contribution the study of the phenomenon of density currents in non-stratified reservoirs, with flows in steady regimes. Flows are analyzed for a wide range of Reynolds and Richardson numbers in the entrance of the reservoir. Based on this hypothesis, a hybrid numeric model is presented considering the Reynolds Transports Equation - focusing on the conservation for volume, mass and momentum - with the intention of obtaining three-dimensional components of velocities, reduced acceleration of gravity and geometric characteristics of currents along the reservoir. It is possible to notice in the numeric simulations, mainly, the need of complementation of the model that refers to the inclusion of the entrainment coefficient and the analysis in the unsteady regime.

Metodologia alternativa ao preenchimento de falhas para a geração de séries de precipitação mensal média de forma automatizada em ambiente SIG

As an alternative to Gap filling in monthly average rainfall series, we attempted to present a methodology for the generation of series only with the observed data available in the rainfall stations present in the study area and its surroundings. For this, a computational tool was developed with a GIS approach, using scripts in the Python language, to automate the study steps. Two calculation alternatives for the mean precipitation, variable Thiessen polygons or variable inverse distance weights (IDW), were considered. Random gaps were imposed from a series of data without gaps allowing us to evaluate the presented methodology. The results of the series calculated according to this methodology were compared to two methods of Gap filling. The behavior of the series was evaluated through the analysis of position and dispersion measurements as well as the temporal behavior by the evaluation of the correlograms and periodograms. The results are found to be satisfactory, which demonstrates the equivalence of the proposal with results found with the gap filling methods under the tested conditions. The differences found between the series were small, which was reflected in the Nash-Sutcliffe Indexes. There were no significant differences between the calculation alternatives by Thiessen polygons or IDW weights.

Evaluation of the laser diffraction method for the measurement of suspended sediment concentration in Mogi-Guaçu reservoir (São Paulo, Brazil)

ABSTRACT The hydrosedimentological monitoring with reliable data of suspended sediment concentration can be problematic when conventional methods are employed because these methods usually show measurements with stations and frequencies lower than desirable, therefore limiting the studies and the management of water resources. In this context, this paper shows a study carried out in the Mogi-Guaçu reservoir (São Paulo, Brazil) in which the correlation of data from sediment in suspension concentration was made, measured with automatic device (LISST-100X) and conventional sampling. By linear regressions and statistical tests, the efficiency of laser diffraction technique was assessed, and the concentrations of suspended sediments were estimated, for both of the performed campaigns. Through the statistical analysis of the results, it was possible to confirm that among all scenarios of linear regressions adopted, the model that divides the reservoir in sectors shows better concentration estimates, inferring that the concentration of suspended sediment has a characteristic behaviour of the segment of the Mogi-Guaçu reservoir. Therefore, the LISST-100X herein proved to be feasible for the case study. It should be noted that the use of this probe made it possible to obtain more data than those obtained using conventional techniques, enabling a more complete analysis of the reservoir and significantly reducing the work in the field, laboratory and office.

Estimating the surface runoff from natural environment data

Purpose The purpose of this paper is to estimate quick and low-cost processes for surface runoff potential on the basis of natural environmental attributes. Design/methodology/approach An approach based on the natural environmental attributes and on the Cook’s method was used for maximal peak flows of surface runoff, as well as for assigning weights to the considered attributes. Used attributes are as follow: steepness, bedrock (lithology), soil (texture, genesis, thickness, and permeability coefficient), drainage density, and favorable features to surface storage. Findings Using natural environmental attributes from previous available studies, adapted from different scales, the authors obtain a low-cost potential surface runoff chart, which can be useful for planning, impact and hazard analysis, and decision purposes in an area without large financial resources, like small communities in developing countries. Despite the common scarcity of data in these communities, often regional basic studies of soil and bedrock are available, making this kind of analysis possible. Originality/value The highlights are quick and low-cost procedures in characterizing the natural environment for planning activities, providing the basis for further detailing, which focus on solving local problems. This approach to runoff estimation allows for the definition of the criteria, considering the potential geodynamic processes. Thus, this kind of study may be very useful for land use planning in developing countries.

Spatial distribution of areas susceptible to sheet erosion in computing environment

Purpose Erosion is the main cause of soil and water degradation, which demands investments for the recovery of such natural resources. The purpose of this paper is to quantify and spatialize soil losses in a municipality with large areas of monoculture of sugarcane. Design/methodology/approach The Universal Soil Loss Equation was applied for the identification of areas susceptible to erosion in the municipality of Jahu, SP, Brazil. Soil maps, statistical census data from Brazilian Institute of Geography and Statistics, radar images from SRTM, rainfall data from Fatec-Jahu hydrometeorological station and digital satellite images from Landsat 5 TM were used for the analyses. Four basic parameters were evaluated: topography of the terrain, rainfall erosivity, soil erodibility, and soil use and management factors. The analyses were conducted in the Geographic Information System (ArcView software). Findings The results show most of the municipality (91 percent) consists of areas of erosion potential. However, the remaining 9 percent can potentially produce 40 percent of the sediment load, which indicates the need for conservation practices and environmental recovery for a reduction in the erosion process acceleration. Originality/value In view of the expansion of sugarcane culture in the cities of Sao Paulo, the results show the importance of a master plan for new areas of sugarcane planting and the need for restoration of riparian vegetation in the surrounding streams and springs for the reduction of erosion.

SUPERFÍCIES ANALÍTICAS COMO MEIO DE AVALIAÇÃO DE ESTRATÉGIAS DE PROCESSAMENTO DE DADOS BATIMÉTRICOS

Reservoirs perform a very important role in the management and planning of water and energy resources of many countries, as Brazil. The storage capacity of a reservoir is directly influenced by erosion processes that occur on its banks and tributaries. Therefore, bathymetric surveys must be conducted for checking the current situation of the reservoirs. In the development of Numerical Elevation Models (NEM), which aim at reproducing the bed surface of a reservoir, the amount and distribution of points that will be collected should be carefully established. The present paper addresses the evaluation of some settings of geometric distributions of points and interpolation algorithms. Trend interpolator showed the smallest volume differences for the circumstances proposed in the study, whereas IDW interpolator exhibited the largest differences. Keywords: Bathymetry; Interpolation; Digital Elevation Model.

Automatização SIG para Espacialização da Disponibilidade Hídrica

The application of regionalization methods is one of the most important procedures for the estimation of the streamflow discharge in ungauged rivers catchments and its automation can reduce both processing time and susceptibility to errors. The Environmental Systems Research Institute (ESRI), in cooperation with the Center for Research in Water Resources at University of Texas (CRWR), has developed the ArcHydro toolset, a geospatial data model designed for hydrological models and used to accumulate attributes in the hydrographical net, among other functionalities. The present paper addresses the automation of the low flow index Q 95 accumulation in the Doce River Basin by ArcHydro and the application of the regionalization method based on the proportionality of the ratio discharge per unit of drainage area. The effects of the reservoirs operation on water availability were computed automatically in this process and reliable results time savings were achieves.

Estudio de las reglas de explotación de los embalses del sistema Cantareira, Sao Paulo Brasil

El rendimiento de un sistema de recursos hidricos es analizado, a traves de simulacion computacional, considerando diferentes politicas de operacion de los embalses. Son utilizados indicadores de rendimiento (garantia, resiliencia, deficit maximo y medio) en la comparacion de las diferentes estrategias de operacion. Los resultados obtenidos en las simulaciones estan, en general, de acuerdo con estudios similares desde el punto de vista de los criterios de rendimiento. Se ha encontrado que la regla de operacion, definida en la “Portaria” del Departamento de Aguas y Energia Electrica-DAEE No 1213, proporciona mejores resultados en relacion a la vulnerabilidad, a costa de una mayor frecuencia de fallos.