The hydrograph at the watershed outlet was simulated using the time-area curve concept implemented in a geographic information system (GIS). The goal of this study was to determine if hydrograph prediction accuracy would be improved by accounting for spatial and temporal variation of excess rainfall. Three models with different methods of estimating excess rainfall were developed: the Distributed Curve Number (DCN) model uses a CN for each cell, generating spatially distributed excess rainfall using the Soil Conservation Services curve number method (SCS, 1972); the Uniform Curve Number (UCN) model uses a single "average" CN for the whole watershed, thus generating a uniform excess rainfall; the Phi index model which uses the Phi-index method to generate uniform excess rainfall. With the aid of a GIS, the cumulative flow time to the watershed outlet is estimated for each cell in the watershed and the isochrones of equal travel time are developed. The time-area curve is developed in the form of an S curve. The spatially distributed 1-hr unit hydrograph is derived from the S curve as the difference between the S curve and its value lagged by 1-hr. The models used in this study describe the physical processes and flow mechanisms. They also reflect effects of watershed characteristics (slope, landuse, soil drainage potential) and excess rainfall intensity on the resulting hydrograph at the watershed outlet. Surface flow is divided into channel flow and overland flow based on the upstream drainage area. Flow is routed to the watershed outlet through a channel network derived from the watershed Digital Elevation Model (DEM). The models developed were tested against observed rainfall-runoff data from the 1153-ha Virginia Piedmont watershed (Owl Run). A total of 30 storms were simulated, with statistical comparison of peak flow rate, time to peak flow rate, and the hydrograph shape. The hydrograph shape was compared both visually and statistically. Results indicated that the two models which account for temporal variation in excess rainfall (DCN and UCN) predicted the output hydrograph much more accurately than the Phi model which lacks the ability to capture the temporal variation of excess rainfall. For this watershed, results showed that the spatial variability in excess rainfall which was accounted for by the DCN model did not improve the prediction accuracy over the UCN model which lacks that ability. However, a sensitivity analysis for the effect of the spatial distribution of the excess rainfall indicated that can be a significant effect of spatial distribution on the predicted hydrograph. / Master of Science

O presente trabalho desenvolve uma proposta para a avaliação da redução da vazão de pico do hidrograma do método racional, no contexto de bacias hidrográficas topograficamente planas. Entendem-se como planas aquelas localidades, cujas declividades médias características e/ou projetadas são inferiores a 0,5%. Pretende-se também neste trabalho apresentar metodologias e práticas de projeto de drenagem usualmente adotadas em regiões de características topográficas semelhantes. No desenvolvimento do estudo, foram discutidas as bases teóricas do Método Racional e outros métodos de avaliação hidrológica que procuram levar em conta o amortecimento da vazão durante o seu escoamento sobre o leito das vias. Apresentam-se também as bases científicas para a criação de um modelo hidrodinâmico a ser usado no estudo para a determinação do fator de redução da vazão de pico do hidrograma racional. A capacidade de escoamento em vias urbanas é então discutida, de forma a se justificar as relações criadas como conclusão do trabalho. O resultado final apresentado é o estabelecimento de uma relação entre a variação do pico da vazão do Método Racional, com a capacidade de armazenamento ou amortecimento de cheias existente nessas vias. Relações estas que, para fins práticos, significam tanto o incremento positivo no período de retorno do projeto, quanto a redução da vazão para efeito de dimensionamento de galerias. Tais resultados são demonstrados de forma prática por meio do estudo de caso no município de Praia Grande, o litoral sul paulista. / This work presents a proposal for estimating the reduction of the Peak Flow Rate determined by the Rational Method, considering flat basins as a main characteristic. It is considered flat, all of those basins in which the average slope on the streets are smaller than 0,5 %. It is also intentions of this work discuss methods and practices adopted to flat areas as urban drainage solutions and best management practices. Within this work, we also present all the theoretical basis of the Rational Method, among others, that try to fuse the street storm water storage capacity whit the conveyance capacity of a usual street. It is also presented theoretical basis of hydrodynamic models to be used as the main tool to determine de peak flow reduction factor of the Rational Method Hydrogram. Conveyance capacity of a usual street is discussed, street storm water conveyance capacity is also discussed in order to justify the relations proposed as a conclusion of this work. As a result of this work it is established a relationship between the Peak flow rate determined by the Rational Method and the street storm water storage capacity. In addition, this peak reduction can be used as a positive increment on the Recurrence Interval or as flow rate reduction when designing the sewerage system, which means implementation costs reduction. An application to the city of Praia Grande, located the Sao Paulo State, is presented and used as a case of study.

O presente trabalho desenvolve uma proposta para a avaliação da redução da vazão de pico do hidrograma do método racional, no contexto de bacias hidrográficas topograficamente planas. Entendem-se como planas aquelas localidades, cujas declividades médias características e/ou projetadas são inferiores a 0,5%. Pretende-se também neste trabalho apresentar metodologias e práticas de projeto de drenagem usualmente adotadas em regiões de características topográficas semelhantes. No desenvolvimento do estudo, foram discutidas as bases teóricas do Método Racional e outros métodos de avaliação hidrológica que procuram levar em conta o amortecimento da vazão durante o seu escoamento sobre o leito das vias. Apresentam-se também as bases científicas para a criação de um modelo hidrodinâmico a ser usado no estudo para a determinação do fator de redução da vazão de pico do hidrograma racional. A capacidade de escoamento em vias urbanas é então discutida, de forma a se justificar as relações criadas como conclusão do trabalho. O resultado final apresentado é o estabelecimento de uma relação entre a variação do pico da vazão do Método Racional, com a capacidade de armazenamento ou amortecimento de cheias existente nessas vias. Relações estas que, para fins práticos, significam tanto o incremento positivo no período de retorno do projeto, quanto a redução da vazão para efeito de dimensionamento de galerias. Tais resultados são demonstrados de forma prática por meio do estudo de caso no município de Praia Grande, o litoral sul paulista. / This work presents a proposal for estimating the reduction of the Peak Flow Rate determined by the Rational Method, considering flat basins as a main characteristic. It is considered flat, all of those basins in which the average slope on the streets are smaller than 0,5 %. It is also intentions of this work discuss methods and practices adopted to flat areas as urban drainage solutions and best management practices. Within this work, we also present all the theoretical basis of the Rational Method, among others, that try to fuse the street storm water storage capacity whit the conveyance capacity of a usual street. It is also presented theoretical basis of hydrodynamic models to be used as the main tool to determine de peak flow reduction factor of the Rational Method Hydrogram. Conveyance capacity of a usual street is discussed, street storm water conveyance capacity is also discussed in order to justify the relations proposed as a conclusion of this work. As a result of this work it is established a relationship between the Peak flow rate determined by the Rational Method and the street storm water storage capacity. In addition, this peak reduction can be used as a positive increment on the Recurrence Interval or as flow rate reduction when designing the sewerage system, which means implementation costs reduction. An application to the city of Praia Grande, located the Sao Paulo State, is presented and used as a case of study.

The aim of the thesis is to set a hydrology model based on existed methodology DesQ-MaxQ, which comes from "Designing flows from a very small catchments" established in 1989. The model is able to set a nearest meteorology station and his 24-hours rainfall depths for periods of repetition 2,5,10,20,50 and 100 years. Substitute rainfall depths are set by "reduction of 24-hours rainfall depths" methodology. According to hydraulic and hydrology conditions of catchment, duration of the critical rains for each period of repetition are set also peak flow rates and total runoffs from the catchment. Application can work in two modes - "one slope" and "two slopes". The second option also includes calculation of design duration for the model catchment and superposition of hydrograph. Application RainRunoff was develop in C# programming language with graphic user interface and option to exports hydrographs.