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A physically based model for estimating the resistance coefficient for coniferous trees in open-channel flow is modified to account for variations in the flexibility between species. The new model is based on the assumption of a linear increase in foliage area with height and a dimensional analysis. It is supported by experiments in air and water. The advantage of the new model over existing methods for estimating resistance factors is its ability to account for the interaction between the vegetation and the flow, taking into account velocity, depth of flow, and vegetative conditions (including type, size, stage of maturity, and density of vegetation). Based on the mathematical model, a table is provided to estimate Manning's n value for flow through vegetation.

Individual pine and cedar tree saplings and branches were used to model the resistance to flow in a water flume for nonsubmerged and nonrigid vegetation to determine the amount that streamlining decreases the drag coefficient and reduces the momentum absorbing area. Currently, vegetation on floodplains is commonly assumed to behave as rigid roughness that can lead to large errors in the relationships between velocity and drag force. This presents a basic fluid mechanics problem. An extreme variation of roughness with depth of flow can result due to a large increase in the momentum absorbing area in nonsubmerged vegetation as depth is increased. This deems all the available roughness equations (which generally are based on relative roughness approach) useless for this application. In this paper a dimensional analysis, supported by experimental results, is developed to obtain a relationship between roughness conditions (i.e., density and flexural rigidity) and flow conditions (i.e., velocity and depth) for floodplains and vegetative zones of natural waterways.

This paper introduces a method for distributed hydrologic modeling that eliminates the need for small computational areas while maintaining the requirement of computing runoff for homogenous watershed subareas. The model is designed from the ground up as a georeferenced model that can make maximum use of remotely sensed data such as rainfall from weather RADAR and land cover characteristics from LANDSAT or SPOT satellites. Other remotely sensed data such as snow-cover extent and initial soil moisture can also be based on satellite data and be directly incorporated in the model. The method consists of grouping hydrologic response units that have similar response characteristics on the basis of classified land-cover maps. Model parameters are unique to individual land-cover classes. This reduces the need for model calibration and allows for the transfer of model parameters in both time and space. The model was applied to four watersheds in Southern Ontario. It was calibrated on the Grand River watershed and then applied to the three other watersheds without further calibration of the hydrologic parameters. Only the river roughness was adjusted.

An evaluation is presented on a study conducted on vegetation and the effects on flow resistance on floodplains and channel banks.

The potential impact of climate change scenarios on the runoff regime in the Italian Alpine area was investigated. A preliminary analysis of the output of three Global Circulation Models (PCM, HADCM, ECHAM) was needed to select IPCC-based scenarios for the 2000-2099 period. Two basins, 1840 and 236 km[sub2] in size, respectively, and with different glaciated areas and storage capacity of reservoirs were selected as case studies. The PCM model, the one capable to better reproduce the observed rainfall regime in the investigated area, with the IPCC SRES A2 scenario was adopted for the meteorological forcing. On average for the two basins, an increase of annual precipitation of about 3% is expected for the 2050 scenario and should not significantly vary at the end of this century compared to present conditions. At the same time temperature should increase of 1.1°C in 2050 and 2.4°C for 2090. Because of the coarse resolution of the climate models' output, the statistics of the simulated rainy days and daily precipitation were adapted to the scale of the two selected basins using a modified version of the multiplicative cascade -model, proposed in the literature to explain the statistics of intermittent fully developed turbulence. As regards to land cover, glaciated areas are decreased, in the future scenarios, according to the Kuhn's concept of equilibrium line adaptation to climate fluctuations. The tree-line altitude is increased, according to the observed trend since the end of the Little Ice Age: thus boundary conditions for evapotranspiration changed. The resulting meteorological variables and hydrological parameters were used to run theWATFLOOD hydrological model in order to assess the changes of runoff regimes in the two watersheds. A decrease of about 7% of annual runoff volume for the 2050 scenario and of 13% for the 2090 scenario was estimated, on average, at the outlet of the Oglio river basin, the largest one. In the smaller Lys basin, where the glaciated area is 8% of the total area, the annual runoff is foreseen to decrease by about 3% (for the 2050 scenario) and 14% at the end of this century. Also the runoff regime changes are significant, with an increase of spring melt and a decrease of summer and autumn runoff. No clear evidence is found for changes in the precipitation extremes and in the fraction of rainy days. [ABSTRACT FROM AUTHOR]