The Soil Conservation Service Curve Number Model is a conceptual model intended for estimating effective rainfall (ER). This model is grounded in a parameter – referred to as Curve Number (CN), which is determined from information on the characteristics of the watershed. The Standard Method (M1) for determining the CN is based on soil and land-use tables; however, some authors have proposed alternative methodologies for defining the CN value from monitored rainfall-runoff events, such as those described by Hawkins (1993) (M2), Soulis and Valiantzas (2012) (M3), and Soulis and Valiantzas (2013) (M4). The objective of this study was to evaluate the impact of using these methods for determination of the CN parameter on the estimation of ER, taking as reference forty rainfall-runoff events monitored between 2015 and 2018 in the Cadeia River Watershed, which has characteristics of the Pampa biome. The different methods assessed for definition of the CN parameter resulted in contrasting performances with respect to the estimation of ER for CRW, as the following findings: i) M1 gave ER values with little reliability, mainly due to the classification of antecedent moisture content classes; ii) M3 provided the best results in determining ER, followed by M2; and iii) the ER values estimated according to M4 differed from those observed, mainly for events with lower rainfall depths.
Acquisition and analysis of hydrological series are essential activities for hydrological studies in watersheds. However, they require time and are usually complex and susceptible to human errors. In order to minimize these problems, computational tools are often used for hydrological analysis, although there are few of them in Brazil. This technical note aims to provide a structured document with information on the motivation, development, conception, main functionalities, and applications of the System of Hydrological Data Acquisition and Analysis (SYHDA). SYHDA is a software intended for acquisition and analysis of hydrological data (rainfall and streamflow) and was fully idealized to enable the user to deal with the country’s leading hydrology databases. It has several modules that include analysis by descriptive statistics and graphical tools, seasonality analysis of streamflows, non-parametric tests, and at-site and regional probabilistic modeling. SYHDA has been used in numerous scientific studies, which give grounds to affirm that it demonstrates a great potential to be used in both everyday and complex activities demanded by the scientific and technical community of hydrology and related areas.
Mathematical models have been widely used to quantify hydrological processes for various practical purposes. These models depend on geomorphological attributes which are derived from relief information represented by Digital Elevation Models (DEM).The objective of this study was to evaluate the infl uence of relief information sources (ASTER, SRTM-30, SRTM-90, and TOPO) over geomorphological characterization of fi ve Brazilian watersheds. Geoprocessing tools were applied for extraction of the following geomorphological attributes for each DEM: drainage area, perimeter, and watershed slope; length and slope of the main stream; total length of streams; bifurcation, stream length and stream area ratios; and length of the highest order stream. The differences in the values of attributes were calculated in relation to the reference DEM (TOPO). It was found that: i) slope of main stream and bifurcation ratio were the most sensitive parameters regarding the relief information source; ii) fl at watersheds were more susceptible to altimetric errors; iii) ASTER did not adequately represent drainage networks for fl at watersheds; and iv) the differences in the geomorphological attributes increased as drainage area decreased. The results indicate that DEM may exert infl uence on the use of hydrological models that depend on geomorphological attributes.
The Xingu River Basin (XRB) in the Brazilian Amazon region has a great relevance to the development of northern Brazil because of the Belo Monte hydropower plant and its crescent agribusiness expansion. This study aimed to evaluate the potential of the Lavras Simulation of the Hydrology (LASH) model to represent the main hydrological processes in the XRB and simulate the hydrological impacts in the face of land-use change scenarios. Following the trend of the most relevant agribusiness evolution in the XRB, four agribusiness scenarios (S) were structured considering the increase in grasslands (S1: 50% over the native forest; S2: 100% over the native forest) and soybean plantations (S3: 50% over the native forest; S4: 100% over native forest). Average hydrographs were simulated, and the frequency duration curves (FDC) and average annual values of the main hydrological components for each scenario were compared. The results showed that, in general, changes in land use based on deforestation in the XRB would lead to an increase in flood streamflow and a reduction in baseflow. The increases in direct surface runoff varied from 4.4% for S1 to 29.8% for S4 scenarios. The reduction in baseflow varied from −1.6% for S1 to −4.9% for S2. These changes were reduced when the entire XRB was analyzed, but notable for the sub-basins in its headwater region, where the scenarios were more effective.
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