1,721,020 research outputs found
Simulation of ground-water flow in steep basin with shallow surface soil
No full textA coupled ground-water/channel flow distributed model has been developed for continuous simulation in a 123-km2 basin. The aim was to analyze the streamflow generation processes in natural vegetated environments. Finite-difference schemes have been used to solve conservation equations of the 2D saturated subsurface flow and the 1D kinematic surface flow. Because of the high hydraulic conductivity of the surface soil, only the saturation excess mechanism of runoff production has been considered. Parameter sensitivity analysis showed the overriding influence of soil storage capacity and conductivity. A grid discretization >100 m produces a hydraulic conductivity greater than physically meaningful, which considerably increases as the space-grid step increases. Results indicate that the model can satisfactorily simulate the water-flow behavior of the catchment after fitting the three parameters of surface hydraulic conductivity, effective porosity, and evapotranspiration losses. These are done after calculating the conductivity as a function of the height of the water table. The simulation efficiency has varied from 87% in the first 5-year calibration period to 85.8% in the subsequent 5-year validation period
Use of network algorithms in spatially distributed models for the study of river basin response
No full textThe research concerns the potential applications of data extracted from topographic maps with GIS for the study of the main physical relations between channel network structures and the runoff generation at the basin scale. It deals with the methodology set up for the automatic channel network extraction, according to the link-based approach, using the DEMs. The channel network is obtained as a rooted tree graph of minimum energy, in which the nodes correspond to the cells resulting from the raster scanning of the basin maps. Pixels with no uncertainty in flow direction are subjected to a local optimization, whereas pixels of equal elevation and pits are globally optimized by an algorithm for the minimum cost network flow problem. Achieved is an excellent correspondence between natural and simulated network, thus confirming the natural system tendency to a minimum energy configuration
Upscaling hydraulic conductivity by means of entropy of terrain curvature representation
Full text linkThe effects of topography resolution on upscaling point-scale processes and parameters on watershed hydrology numerical routing are investigated. Parsimonious continuous simulation was applied to two forested catchments with shallow and sloping soils, one medium (123 km2) and one small-sized (4.5 km2), where saturation-excess runoff prevails. The computed discharge showed highest sensitivity to spatial resolution, due to smoothing effects during aggregation of the digital elevation model caused by a coarse grid. The loss of information content of terrain curvature as consequence of the averaging procedure was related to the amplification factor required for the soil hydraulic conductivity, to compensate the resulting retardation of the runoff hydrograph. A scaling relation has been developed that links soil hydraulic conductivity measured at the point-scale with that required at the typically much coarser modeling scale. The entropy concept for the measurement of information loss could be a good index for parameter rescaling of other basins where the terrain curvature is similarly scale-dependen
Numerical dissipation and parameter values in the distributed hydrological modeling’
No full textA coupled subsurface-channel flow distributed model has been applied for the continuous simulation of the basic hydrologic processes in a small mountain basin, in order to investigate the effects of the numerical resolution on parameter evaluation and on simulation results. Finite difference schemes have been used to solve conservation equations of the 2-D saturated subsurface flow and the 1-D kinematic surface flow. Simulation tests developed in terms of space and time-steps have highlighted that the truncation error in the finite difference approximation of groundwater flow equation, produces a numerical dissipation which grows as the space-step grows. This numerical dissipation can be compensated adopting hydraulic conductivity greater than physically meaningful values. The conductivity parameter can take on field measured values if a space-step is used which is smaller than 10 m. For greater grid scales, the conductivity parameter needs to be recalibrated and it must be chosen empirically with increasing values as the grid size increases
Studio idraulico delle correnti e della salinità in uno stagno costiero
No full textEnvironmental monitoring and a study of the tidal cur-rents was carried out on a coastal lagoon in a wetland area of Northern Sardinia. This was done as part of a research project to exploit the fish resources in an ecologically compatible way. The relative shallowness of the lagoon in relationship to its surface area allows to use a two-dimensional depth-averaged hydrodynamic and diffusive model. The coupling of the alternative directional implicit difference scheme and the Eulerian-Lagrangian method is used to solved the shallow water equations. The hydrodynamic equilibrium of the lagoon is determined by the tidal currents and by fresh water from the catchment. The tide waves which enter the lagoon are not dampened in amplitude, and there is only a small time lag in the effects of the tide in the whole lagoon. The friction coefficient and the turbulent kinetic viscosity have been evaluated by comparison with the collected field data. The spatial and temporal distribution of the salinity has been used to calibrate the diffusion model and validate the hydrodynamic model
Indagini sul sistema idraulico del lago di Baratz per la gestione e la salvaguardia ambientale dell’area
No full textMonitoraggio ambientale e modelli di simulazione per la regolazione idraulica e la salvaguardia dello stagno di Calich – Alghero
No full textParameter values and grid size in the distributed hydrological modeling for a small mountain basin
No full textA finite difference distributed model for the continuous simulation of the coupled groundwater-channel flow has been applied to a 4.56-km2 vegetated mountain basin. The effects of the numerical dissipation of the difference schemes adopted are investigated using different space and time-step sizes. Saturated subsurface flow is simplified to a 2-D horizontal representation by integrating over the soil depth. Surface flow is simplified to a kinematic 1-D representation along the channel network. Groundwater and stream channel components of the hydrological cycle are simulated with the mass and momentum conservation equations. The comparison of the discharge hydrographs for four grid-step sizes has highlighted that the truncation error of the higher order terms in the finite difference approximation of groundwater flow equation, produces a numerical dissipation which grows as the space-step size grows. This numerical dissipation can be compensated adopting new soil hydraulic conductivity values, greater than physically meaningful values, which considerably increase proportionally to the grid-step size. The conductivity parameter can then take on field measured values only if a small space-step is used
Gestione multisettoriale e criticità dei sistemi idrici: il caso della Sardegna settentrionale
No full textHydrological processes of a closed catchment-lake system in a semi-arid Mediterranean environment
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