Abstract. Base-level maps (or "isobase maps", as originally defined by Filosofov, 1960), express a relationship between valley order and topography. The base-level map can be seen as a "simplified" version of the original topographic surface, from which the "noise" of the low-order stream erosion was removed. This method is able to identify areas with possible tectonic influence even within lithologically uniform domains. Base-level maps have been recently applied in semi-detail scale (e.g., 1:50 000 or larger) morphotectonic analysis. In this paper, we present an evaluation of the method's applicability in regional-scale analysis (e.g., 1:250 000 or smaller). A test area was selected in northern Brazil, at the lower course of the Araguaia and Tocantins rivers. The drainage network extracted from SRTM30 PLUS DEMs with spatial resolution of approximately 900 m was visually compared with available topographic maps and considered to be compatible with a 1:1,000 000 scale. Regarding the interpretation of regional-scale morphostructures, the map constructed with 2nd and 3rd-order valleys was considered to present the best results. Some of the interpreted base-level anomalies correspond to important shear zones and geological contacts present in the 1:5 000 000 Geological Map of South America. Others have no correspondence with mapped Precambrian structures and are considered to represent younger, probably neotectonic, features. A strong E-W orientation of the base-level lines over the inflexion of the Araguaia and Tocantins rivers, suggest a major drainage capture. A N-S topographic swath profile over the Tocantins and Araguaia rivers reveals a topographic pattern which, allied with seismic data showing a roughly N-S direction of extension in the area, lead us to interpret this lineament as an E-W, southward-dipping normal fault. There is also a good visual correspondence between the base-level lineaments and Correspondence to: C. H. Grohmann (guano@usp.br) geophysical anomalies. A NW-SE lineament in the southeast of the study area partially corresponds to the northern border of the Mosquito lava field, of Jurassic age, and a NW-SE lineament traced in the northeastern sector of the study area can be interpreted as the Picos-Santa Inês lineament, identifiable in geophysical maps but with little expression in hypsometric or topographic maps.

River stage-discharge relationship has an important impact on modeling, planning, and management of river basins and water resources. In this study, the capability of Gaussian Process Regressions (GPR) kernel-based approach was assessed in predicting the daily river stage-discharge (RSD) relationship. Three successive hydrometric stations of Housatonic River were considered and based on the flow characteristics during the period of 2002–2006 several models were developed and tested via GPR. To enhance the applied model efficiency, two pre-processing techniques namely Wavelet Transform (WT) and Ensemble Empirical Mode Decomposition (EEMD) were used. Also, two states of the RSD modeling were investigated. In the state 1, each station's own data was used and in the state 2, the upstream stations’ datasets were used as input to model the RSD at downstream of the river. The single and integrated models results showed that the integrated WT- and EEMD-GPR models resulted in more accurate outcomes. Data processing enhanced the models capability between 25 and 40%. The results showed that the RSD modeling in the state 1 led to better results; however, when the stations’ own data were not available the integrated methods could be applied successfully for the RSD modeling using the previous stations’ data.

Base-level maps (or "isobase maps", as originally defined by Filosofov, 1960), express a relationship between valley order and topography. The base-level map can be seen as a "simplified" version of the original topographic surface, from which was removed the "noise" of the low-order streams erosion. This method is able to identify areas with possible tectonic influence even within lithological uniform domains. Base-level maps are usually applied in semi-detail scale (e.g., 1:50 000 or larger) morphotectonic analysis. In this paper, we present an evaluation of the method's applicability in regional-scale analysis (e.g., 1:250 000 or smaller). A test area was selected in Northern Brazil, at the lower course of the Araguaia and Tocantins rivers. The method provided results consistent with the scale of the data used as topographic base and with the drainage network (1:1 000 000). Some of the base-level anomalies interpreted correspond to important faultlines and geological contacts present at the 1:5 000 000 Geological Map of South America. Others have no correspondence with mapped structures and are considered to represent more recent morphotectonic features. The E–W inflexion of the lower Tocantins is considered as a major drainage capture, originated by an E–W, southward-dipping normal fault. The base-level map also presented a good correlation with anomalies in geophysical data, which shows that the method is sensitive enough to detect features with little topographic expression