1,720,966 research outputs found
Effetti dei fenomeni di filtrazione sulle traverse fluviali e sulle opere provvisionali di comune impiego nelle costruzioni idrauliche
No full textHow is hydrology improving?
No full textThere are as many ways of evaluating performances of hydrological models as purposes
to represent phenomena of interest and aspects of water cycle which to focus on. There
is no single criterion satisfying all assessment practices. Despite this obvious limitation,
the article attempts to identify some statistical indicators with which to answer the general
question: whether it is progressing and how the effectiveness of hydrological modelling at
large. From examples published on international journals and from case studies taken
from documents by the main international hydrological organizations, spanning over a
period of about 35 years, a statistical analysis is made separately for models predicting 1)
low flows, 2) peak events, 3) whole cycle. The reported performance indexes (mainly
determination or correlation coefficients) are plotted against time, to check the overall
trend. Time is not the best explanatory variable but, although linearly, it summarizes the
non linear increase of means: numerical codes, data availability from new gauging tools,
human and financial resources, attention and effort paid to this branch of science. The
overall trend is of course positive but less than expected and, moreover, in the last 15
years, in spite of new analysis techniques, it seems to show an asymptote far from unity.
Is this a boundary provided by the mathematical representation or by the description of
physical systems and their forcing actions? Has the knowableness of a hydrological
system an upper limit which cannot be exceeded by the usual methods of numerical
simulation? Has the calibration-validation approach to be revised? How is hydrological
modelling effective in practice? Is there an ideal set of data and of experiments which
allows a given model to perform at its best? How far are we usually from this optimal
condition when running hydrological codes? How can this distance be measured from the
very beginning of the task? Some tentative hypotheses are made to answer these
questions
Navigazione interna: la rete idroviaria padana. Connessioni con la portualità marittima
No full textPhysically based model of soil erosion and pollutant dynamics at a basin scale
No full textIn the paper we describe a conceptual model for evaluating sediment transport and pollutants dynamics (BOD, P and N) at a basin scale. The sediment transport model is physically based; the pollutant dynamics model is based on an integral and simplified form of the complex equations. The model was numerically implemented and applied to four catchments in the Po River Area, with extension ranging from 460 to 2150 km2. The topology is described by DEM with cells of 250x250 m2. The time step is of 24 h. The model was calibrated using data measured in the main streams in the period 1993-1999
Flood prevention analyses in artificially drained basins: lithology, land use and hydrology.
No full textAn interdisciplinary study is presented dealing with the flood prevention techniques designed and applied to two artificially drained basins in Northern Italy (Parma Province). The analyses include lithological, land use, hydrological, hydrodynamic and environmental aspects, in addition to structural and economical computations.
This poster (Part 1) comprises lithology, land use and hydrology, while Part 2 describes hydraulic and ecological studies, although many subjects are coupled and a distinction in the information and modelling flow cannot be sharply traced.
The Lorno and Galasso Channels are the main outlets of two adjacent basins, whose areas are 20.8 and 91.3 km2 respectively. Their catchments are both very flat and are drained by a dense network of smaller artificial canals whose bed slope is often much less than 1m•km-1: during the flood events the driving energy is provided by the water surface slope. The main channels share the final reach of 0.5 km just before their common outlet in Parma River, which in its turn flows into Po River 8 km down-stream. High stages in both Rivers cause huge backwater effects in the final 8 km of Lorno and the final 4 km of Galasso main Channels: to prevent the flood risks to the densely populated and historical town of Colorno, a lock is operating at the con-fluence of the channels, whose movable gates close whenever water level down-stream gets higher than upstream, so disconnecting both artificial channels from the natural streams.
While floods in Parma River are comparatively short (hours), floods in Po River may last weeks: moreover they usually happen during the fall season when high flows in the Lorno e Galasso basins are most likely to occur, lasting days. So in the October-December period, the joint probability of high water stages downstream of the lock, causing the closure of the gates, and of high discharge from the upstream catchments is not negligible: the probability of upstream water levels exceeding the local levees is therefore higher than the usually accepted standards for hydraulic safety.
From the lithological point of view, the soil within the region around the channels outlet is mainly silt and clay: till the XIX century it was a marshy area, with a complex ecological system, where many species of birds found their dwelling.
In conjunction with the project of three clay open quarries for the local brick industry, the analyses aim at ascertaining if these structures, once exploited, might be trans-formed and operate both as qualified ecological sites where the original natural environment can be restored, and as hydraulic devices (lateral reservoirs) to reduce the local risk of flooding.
Part I of the paper describes the lithology and land use in Lorno and Galasso basins, together with hydrological evaluations and modelling. In particular the following aspects are presented:
A) Zonation of overall catchment area into smaller tributary sub-basins; check of topology, functioning and efficiency of the drainage network; evaluation of morphological, lithological and land use features of sub-basins sides in view of the overland processes; evaluation of morphological and hydraulic properties of each canal within the drainage system, in view of the channel processes.
B) Rainfall analysis, focussing on the statistics of extreme event likely to generate the flood waves relevant to the hydrodynamic modelling in the main channels, to the design of flood prevention devices and to the risk analysis of the system.
C) Through hydrological simulation, evaluation of probabilistic flood hydrographs as a function of return time likely to occur within the drainage system; evaluation of the joint probability distribution of downstream boundary water stages (Po and Parma Rivers) and discharge hydrographs in Lorno and Galasso basins
Flood prevention analyses in artificially drained basins : hydraulics and ecology.
No full textAn interdisciplinary study is presented dealing with the flood prevention techniques designed and applied to two artificially drained basins in Northern Italy (Lorno and Galasso, Parma Province). The analyses about lithology, land use and hydrology are described in Part I of the paper; Part II summarizes hydraulic and environmental aspects.
As previously mentioned, many subjects are coupled and a sharp distinction in the information and modelling flow cannot be traced. In particular lack of discharge time series entails a complex coupling of hydrological and hydrodynamic modelling in order to correctly estimate the discharge hydrographs as a function of probability which enter the artificial drainage network from each contributing sub-basin and which propagate along the main channels to build the shape and the volume of the flood wave flowing in the critical final reach of the system, where flooding threatens the populated town of Colorno.
The calibration of the rainfall-runoff hydrological model and the hydrodynamic model, based on the numerical integration of the classical Saint Venant equations, is performed by a trial-and-error procedure trying to match the records dates and effects of flooding, available for the last 60 years in the drainage network and in its downstream reach in particular. The procedure depends on the description of the channel geometry varying along the decades.The hydrological model is run for the rainfall events which caused some flooding and the corresponding hydrographs are routed through the hydrodynamic code: its results are compared with the local historical observations, in terms of time and place of water levels exceeding bank elevation. Model parameters (both hydrological and hydrodynamic) are adjusted deviating as little as possible from central value of their distributions.
After calibration, the following aspects are dealt with:
A) Hydrodynamic simulation of the behaviour of the critical reach of Lorno and Galasso main channels, under the probabilistic discharge hydrographs in the unmodified configuration, for various downstream boundary conditions (open and closed lock gates).
B) Evaluation of the effects on flood risk reduction when lateral reservoirs are introduced where in the next future three open quarries will make a large storage volume available.
C) Evaluation of the optimal design of the reservoirs in order to foster the ecological restoration of the site, where many birds are expected to find their natural dwelling; design of hydraulic structures to enhance the environmental function by minimizing the impact of periodical flooding.
The problem of uncertainty in the numerical estimates is also addressed, by conducting a sensitivity analysis over the most important parameters in the hydrological and hydrodynamic simulations
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