Kazi Rahman

Quantification of the daily dynamics of streamflow components in a small alpine watershed in Switzerland using end member mixing analysis

There is a growing need to improve our understanding of catchment flow generation processes, especially in alpine watersheds, where the aquatic biodiversity is dependent upon the types of water sources and their seasonal dynamics. In order to identify and quantify the potential sources that contribute to stream runoff, Water samples were collected and discharge was measured. Other physical variables like electric conductivity and water temperature were also collected twice a day, once in the morning and once in the evening. These measurements continued for two to four consecutive days. In situ measurements were done for temperature, electric conductivity and turbidity of water at different temporal scale. Mass spectrometry was done to analyze silica and sulfate along with chlorine. Three different water sources were identified based on their physiochemical characteristics: glacier melt water, quickly routed surface runoff, and slowly routed ground water. Principal component analysis was performed in order to reduce dimensionality of the chemistry data independently in two hydrological years. End member mixing analysis was carried out for morning and afternoon data to describe the daily variation of runoff components. Our study suggests that glacier melt component has a strong daily variation, which influences the magnitude and timing of peak flow. A sign of early melt and accumulation can be seen in this watershed based on the studied years.

Breaking walls towards fully open source hydrological modeling

Hydrological models are powerful mathematical tools to address environmental problems and are often used for watershed management and planning. Hydrological models are data driven and the lack of data availability often limits model development. In this paper, we address several challenges in building and running a hydrological model for streamflow simulations based solely on freely available data and open source software. The Soil and Water Assessment Tool (SWAT) hydrological modeling software has been used in the Map Window Geographic Information System (GIS). All spatial and non-spatial data used in this study were obtained from various free of charge online sources. Model calibration and validation represent major challenges following the initial model construction since they involve several trial and error processes to reach acceptable model performances. These critical steps were programmed here as automated scripts in the R open source statistical package. The challenges of model building are described step by step through video tutorials. Using a case study in the Mendoza watershed in Argentina, we show that simulated streamflow exhibits sound agreement with the observed streamflow considering daily time steps (NSE = 0.69, R2 = 0.72 and Percent bias = +9%). The workflow demonstrated in this study can be applied for other watersheds, especially in data-sparse regions that may lack key regional or local data sets.