José Márcio Alves da Silva

Modelo para a determinação do espaçamento entre desaguadouros em estradas não pavimentadas

As estradas nao pavimentadas sao de fundamental importância para o desenvolvimento social e economico do Brasil, sendo a erosao provocada pela agua no leito e nas margens destas estradas um dos principais fatores para sua degradacao. Neste artigo, apresenta-se um novo modelo para a determinacao do espacamento entre desaguadouros em estradas nao pavimentadas e, consequentemente, para a reducao dos problemas associados a erosao hidrica. Utilizando o modelo de ondas cinematicas, determina-se o hidrograma de escoamento superficial no canal de drenagem da estrada e, a partir deste, e calculada a tensao provocada pelo escoamento. Sempre que a tensao cisalhante causada pelo escoamento supera a tensao critica para cisalhamento do solo ocorre o seu desprendimento. A diferenca entre essas tensoes cisalhantes e multiplicada pela erodibilidade do solo e pela area em que ocorre a aplicacao da tensao cisalhante para estimar a perda de solo provocada pelo escoamento. O espacamento maximo entre desaguadouros e obtido, comparando-se a perda de solo provocada pelo escoamento com a perda de solo toleravel. O comprimento maximo do canal e aquele para o qual a perda toleravel e atingida. O modelo permite determinar o espacamento entre desaguadouros considerando as caracteristicas das areas que contribuem para o escoamento e a resistencia do solo. As simulacoes realizadas mostraram que o modelo e sensivel as alteracoes na erodibilidade e na tensao critica de cisalhamento do solo, bem como a declividade do canal, permitindo ainda que, por meio da alteracao no aprofundamento toleravel para o canal, os espacamentos possam ser ampliados ou reduzidos.

Impact of the substitution of reference annual streamflow by monthly streamflow on the potential use of water resources

The consideration of the streamflow seasonality has a high potential to improve the water use. In order to give subsidies to the optimization of water use, it was evaluated the impact of the change of reference annual streamflow by the monthly streamflows in the potential water use throughout the hydrography of Paracatu sub-Basin. It was evaluated the impact on Q7,10 (lowest average streamflow during a 7-day period with an average recurrence of 10 years) and on Q95 (permanent flow present 95% of the time). The use of monthly streamflow to substitute the annual streamflow had a high potential of improvement of water resources use in the sub-Basin studied. The use of monthly Q 7,10 in substitution of annual Q 7,10 increases the potential water use that vary from about 10% in the months of lower water availability to values exceeding 200% in the months with higher availability of surface water resources. The use of monthly Q95 in substitution of the annual Q95 implies in changes oscillating from reduction of 37% in months of higher water restriction to values exceeding 100% in the months of higher availability, so the use of monthly Q95 instead of the annual Q95 enables the more rational and safe use of water resources.

Metodologia para obtenção do hidrograma de escoamento superficial em encostas e canais. Parte I: desenvolvimento e avaliação

It was developed a methodology that allows obtaining the hydrograph of superficial flow and maxim flow of any position along a hillside and transversal sections of canals. The area of the hillside is divided in a matrix system having 100 lines and 100 columns. It was considered that the flux occurs in the direction of the hillsides slope and the flow of each pixel is the addition between its own flow and the flows that come from the pixels that contribute to the superficial flow in the pixel under analysis. In the canal the flow is taken as the addition of the hydrographs that come from the columns in the reticular system. By the new methodology the comparison of the total volume and maximum surface runoff flow values, obtained in two experimental conditions (hillside and hydrographic basin), allowed to conclude that the new model provided good performance when compared to the Rational Method and the Curve Number Method.

Metodologia para obtenção do hidrograma de escoamento superficial em encostas e canais. Parte II: modelo computacional e análise de sensibilidade

Estimative of maximum runoff flow rates are essential for the projects of hydraulic urban and rural basins. The difficulty in applying the available procedures to estimate the temporary variation of the flow rate and its maximum value is due to the inaccuracy of some methods that are usually used and to the big variability of results that can be obtained by different professionals that use the same procedures. Therefore, research of a method that produces trustworthy assessment of peak-flow rates and hydrographs is of great interest. This paper describes the development and sensitivity analysis of a software (HIDROGRAMA 2.1) that allows obtaining surface runoff hydrograph, peak flow rate and its time of occurrence, runoff maximum height, runoff velocity and runoff volume. The model presented great sensibility to precipitation return period, infiltration rate after long time of wetting and hillside and channel length.