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Editorial: River basin hydrology and natural hazards: Monitoring, prediction and prevention
Abstract
The 5th edition of the ‘Hydrology Days’ of the Italian Hydrological Society was held in Perugia, Italy, 6–8 October 2015, to provide a joint forum of hydrologists and a broad range of stakeholders for commenting and discussing on ‘River basin hydrology and natural hazards: monitoring, prediction and prevention’. A total of 58 abstracts were presented at the workshop. The 2½-day conference was organized by the ‘Hydrology Group’ of the Research Institute for Geo-Hydrological Protection (National Research Council of Italy) in collaboration with the Italian Hydrological Society, the Tiber River Basin Authority and the professional association of Engineers of Perugia. Specifically, the Italian Hydrological Society (SII-IHS) was founded in 2009 to foster progress, enhancement and dissemination of hydrological sciences in Italy, including all aspects related to water resources systems management and possible interaction with human activity. In this perspective, one of the main objectives of the Association is to stimulate interdisciplinary collaboration among academia, research institutes, institutional stakeholders and private operators.
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The paper presents the activity performed at the University of Brescia by students and researchers, belonging to different Mediterranean cultures and different disciplines, to prepare a documentary exhibition on irrigation techniques in water scarcity conditions, on the occasion of the International Year of Soils 2015. Traditional irrigation techniques were identified as a key aspect of soil conservation and agricultural practices, to build living and autopoietic ecosystems, also in adverse climatic conditions, and to adapt to climatic changes. Being a structural source of ecosystem survival, and being based on long-lasting observation of the climate and of the environment, they have deep roots in local cultures and they were identified as a common ground also for multicultural interaction. The core of the exhibition is structured in sections focused on techniques for collecting groundwater, atmospheric humidity and surface water, on water lifting techniques and on water distributive systems. The final section of the exhibition is devoted to the oases which are presented as an equilibrium ecosystem, established upon the alliance between man and nature and founded on the capability of collecting water.
Increased water demand and climate change impacts have recently enhanced the need to improve water resources management, even in those areas which traditionally have an abundant supply of water, such as the Po Valley in northern Italy. The highest consumption of water is devoted to irrigation for agricultural production, and so it is in this area that efforts have to be focused to study possible interventions. Meeting and optimizing the consumption of water for irrigation also means making more resources available for drinking water and industrial use, and maintaining an optimal state of the environment. In this study we show the effectiveness of the combined use of numerical weather predictions and hydrological modelling to forecast soil moisture and crop water requirement in order to optimize irrigation scheduling. This system combines state of the art mathematical models and new technologies for environmental monitoring, merging ground observed data with Earth observations from space and unconventional information from the cyberspace through crowdsourcing.
The estimation of velocity profile in turbulent open channels is a difficult task due to the significant effects of the secondary flow. The present paper investigates the mechanism of the velocity-dip phenomenon, whereby the location of the maximum velocity appears below the free surface. Previous studies conducted in straight channels relate the mechanism of the velocity-dip phenomenon to secondary flow induced by anisotropy of turbulence. This work focuses on high-curved channels where the secondary motion, which is also induced by the channel’s curvature, evolves along the bend. The width-to-depth ratio, B/h, is one of the most important parameters affecting the secondary motion entity. In particular, the present study aims to investigate the evolution of the velocity-dip along the bend for two values of the width-to-depth ratio and the applicability of the entropic model for the dip-phenomenon estimation. The results show that the velocity-dip is more accentuated for low values of the width-to-depth ratio, where the secondary motion plays a fundamental role in the distribution of the downstream flow velocity, although the velocity-dip is also present when the aspect ratio is higher than 10. Furthermore, the velocity profiles estimated by applying the entropic model are in good agreement with the measured ones, especially for B/h<10.
The utilization of continuous approaches, namely analytical-probabilistic methods, has often been advocated for hydraulic device sizing, in order to overcome some deficiencies of the design event method. In the analytical distribution derivation, however, strong simplifying hypotheses are usually adopted. Rainfall depth and duration independency is the most unrealistic one, even if usually leads to satisfactory agreements between derived and benchmarking distributions. The reason can lie in drawbacks related to conventional assessment techniques of multivariate rainfall distributions. Copula functions recently provided a significant improvement in statistical inference capabilities and greatly simplified the distribution assessment. Nonetheless, the generalization of the return period concept, well defined in the univariate case, to multivariate cases has not found a blanket solution yet. Effective estimate methods can however be developed for the design and performance assessment of specific hydraulic devices. In the regard of urban catchment applications, a criterion to derive flood frequency curves from a rainfall volume and duration distribution is herein proposed. Further, a method to estimate the return period of bivariate rainfall events based on a device-targeted approach is developed. Hydrologic simulations are conducted to support model reliability through a test case, featured by a northern Italy’s rainfall regime.
Estimating water requirements of plants cultivated in greenhouse environments is crucial, both for the design of greenhouse irrigation systems and the improvement of irrigation scheduling. Spinach is one of the main vegetables sold as ‘ready-to-eat’ bagged produce; it is very sensitive to water stress and thus requires accurate irrigation. In this work, a water balance model simulating the daily irrigation need for greenhouse crops based on the FAO-56 ‘single crop coefficient’ method was designed and applied (FAO-56-GH). Two experiments were conducted on two spinach varieties grown in pots in different periods. For each experiment, four nitrogen treatments were considered. Irrigation was managed weighing the pots every day, and restoring soil water to field capacity. Crop coefficient (Kc) values were calibrated using data of the first experiment, the model was successively validated using the second dataset. Results showed a good model performance both in the validation and calibration periods (R2 = 0.80 and 0.84, root mean square error (RMSE) = 0.41 and 0.21 mm day−1, Nash–Sutcliffe efficiency (NSE) = 0.78 and 0.83). Analysis of variance (ANOVA) test revealed a scarce dependence of irrigation needs to nitrogen treatments. This study suggests the possibility of adopting the FAO-56-GH model with site-specific Kc to improve irrigation management and planning in greenhouse environments.
Extensive flooding can be the result of levee system failures most frequently caused by the piping process due to seepage. The proper description of the seepage line is affected by the difficulty of estimating the hydraulic parameters, mainly the soil hydraulic conductivity. Therefore, the development of simple methods for a quick analysis of extended levee systems is fundamental to identify critical points. In this context, a practical procedure, recently proposed, based on a simple vulnerability index is here enhanced and used to derive diagrams easily applicable for seepage vulnerability estimate, taking the hydraulic parameters’ uncertainty into account. The procedure is applied for the Tiber River, in central Italy, and the Tanaro River, in northern Italy, by analyzing 67 and 6 levees, respectively. The results show that the method provides the highest seepage probabilities for levees affected by failures in the past. Therefore, the procedure seems to be able to identify the levees that require detailed investigations. Finally, the Italian levee database (DANTE) is presented as a dynamic geospatial tool for collecting all the available data/information on levee systems to usefully support authorities with the charge of hydraulic risk mitigation for identifying the most vulnerable levees.
A statistical analysis of the rainfalls is carried out for detecting a possible trend in the observed data. The rainfall dataset refers to the historical series collected in the hydrographic basins of the Marche region. On the one hand, the annual maximum daily, hourly and sub-hourly rainfalls have been analysed, on the other hand Climate Change Indices by Expert Team on Climate Change Detection and Indices (ETCCDI) (R1 mm, Rx1day, R20 mm, R95pTOT, PRCPTOT) have been computed to verify an eventual variation of the frequency of the rainfall regime in the Marche region. The time series, selected in the reference period 1951–2013, have been processed by using the non-parametric Mann–Kendall test. The results confirm that most of the series relating to the annual maximum rainfalls do not exhibit any trend. The absence of trend or the presence of negative trend prevail also in the analysis of the ETCCDI indices. The annual average anomalies of the same indices computed with respect to the climatological reference period 1961–1990 are negative since the mid-1980s, but they appear to show an increasing behaviour in the period 2009–2013.
This paper presents a procedure for estimating discharge in a river cross-section based on the combined use of dimensionless isovels and point velocity measurements. Specifically, taking the Biot–Savart law on the magnetic field induced by an electric current in a wire as their basis as already done by other researchers, the authors propose a new formulation of the relationship characterizing the effect of the wetted perimeter on the range of velocities in a cross-section in order to take explicit account of roughness, expressed by means of Manning's coefficient. Once appropriately nondimensionalized, the isoeffect contours can be read as dimensionless isovels. Assuming in situ velocity measurements are available, discharge at a cross-section can be computed using two different methods. The proposed procedure was applied to six case studies characterized by river cross-sections which differed greatly from one another. The results show that the two methods proposed for estimating discharge lead to equivalent outcomes, and in all the cases the procedure as a whole enables a sufficiently accurate estimation of discharge, even when it is based on a limited number of velocity measurements or on the measurement of maximum surface-water velocity alone.
The suitability of a smartphone camera for the structure from motion (SfM) reconstruction for monitoring variations in soil surface characteristics and soil loss originated by a low intensity erosive event was evaluated. Terrestrial laser scanning (TLS) was used to validate the SfM model. Two surveys of the soil surface, one before and one after the rainfall event, were carried out for SfM and TLS. The point clouds obtained by the SfM were compared to the TLS point clouds (used as reference). From the point clouds, digital elevation models (DEMs) (0.01 m × 0.01 m) were obtained. The differences of the DEMs (DoDs) obtained from the two surveys for SfM and TLS were compared. To assess the uncertainty of the DEMs, from the DoDs the minimum level of detection was derived. The soil loss was evaluated from DoDs (for SfM and TLS, respectively) considering negative values as erosion and positive values as deposition. The SfM appears appropriate and sensitive for detecting small soil surface variations induced by low erosive events. The SfM estimated correctly the measured soil loss, while TLS underestimated 26%. Further studies could be carried out to consolidate these first results.
Standardized indices are widely used in the spatio-temporal monitoring of several hydrological variables. The estimation of these indices is affected by uncertainty which depends on the methods adopted for their quantification and on the characteristics (i.e., size and variability) of the available sample of observations. In this paper various uncertainty measures, applicable to any kind of standardized index, are proposed. These measures derive from bootstrap-based confidence intervals expressed in years of return period and are effective for assessing both the uncertainty and the reliability of the index estimate. In the illustrative case study the indices considered are the Standardized Precipitation Index and the Standardized Precipitation Evapotranspiration Index. Their time series have been quantified by both nonparametric and parametric approaches, using the weather data of a single station in central Italy. For the parametric approach, two possible types of distributions have been assumed for each index. The results are discussed in order to analyze the behavior of the proposed uncertainty measures in relation to: sample size, type of approach (parametric or nonparametric), time scale, type of standardized index, and type of anomaly (excess or deficit).
Parameter estimation for rainfall-runoff models in ungauged basins is a key aspect for a wide range
of applications where streamflow predictions from a hydrological model can be used. The need for
more reliable estimation of flow in data scarcity conditions is, in fact, thoroughly related to the
necessity of reducing uncertainty associated with parameter estimation. This study extends the
application of a Bayesian procedure that, given a generic rainfall-runoff model, allows for the
assessment of posterior parameter distribution, using a regional estimate of ‘hydrological signatures’
available in ungauged basins. A set of eight catchments located in southern Italy was analyzed, and
regionalized, and the first three L-moments of annual streamflow maxima were considered as
signatures. Specifically, the effects of conditioning posterior model parameter distribution under
different sets of signatures and the role played by uncertainty in their regional estimates were
investigated with specific reference to the application of rainfall-runoff models in design flood
estimation. For this purpose, the continuous simulation approach was employed and compared to
purely statistical methods. The obtained results confirm the potential of the proposed methodology
and that the use of the available regional information enables a reduction of the uncertainty of
rainfall-runoff models in applications to ungauged basins.
The investigation of a few hydrological processes under natural conditions can be distorted by their interactions. In this context, a laboratory system that allows a few mechanisms of the infiltration process to be studied univocally is presented. The core component of the system is a physical model consisting of a soil tank with slope angle, γ, adjustable from 1 ° to 15 °. A generator of artificial rainfall can produce rainfall rates up to 50 mm h⁻¹. Surface runoff and deep flow, Qd, are continuously monitored. An overall analysis of three previous investigations performed by the physical system and directed to clarify the infiltration process is also briefly reported. These investigations, that concerned the validation of a local conceptual model for erratic rainfalls, the role of run-on and the effects of sloping soil surfaces, were all carried out by using different configurations of the system. Great slope effects in bare soils were observed. For example, under steady conditions, a ratio Qd(γ = 1 °) / Qd(γ = 10 °) equal to about 4 was observed in a loam soil. Finally, on the basis of the acquired knowledge, further investigations to be realized with the same basic elements are proposed to derive a conceptual model that describes the soil surface gradient effects.
Fully remote surface flow measurements are crucial for flow monitoring during floods and in difficult-to-access areas. Recently, optics-based surface flow monitoring has been enabled through a permanent gauge-cam station on the Tiber River, Rome, Italy. Therein, a system of lasers and an internet protocol camera equipped with two optical modules afford video acquisitions of the river surface every 10 minutes. In this work, we establish a standard video-processing protocol by analyzing more than 10 Gb of footage data captured during low discharge regime from May, 2nd to 11th, 2015, through particle tracking velocimetry (PTV). We show that good image-based velocity data can be obtained throughout the day–from 6 am to 8 pm–despite the challenging experimental settings (direct sunlight illumination, mirror-like river surface, and overlying bridge shadow). Further, we demonstrate that images captured with a 27 ° angle of view optical sensor lead to average velocity measurements in agreement with available radar data. Consistent with similar optical methods, PTV is not applicable in case of adverse illumination and at night; however, it is more robust for dishomogeneous distributions of floaters in the field of view.
Many rainfall-runoff (RR) models are available in the scientific literature. Selecting the best structure and parameterization for a model is not straightforward and depends on a wide number of factors, including climatic conditions, catchment characteristics, temporal/spatial resolution and model objectives.
In this study, the RR model MISDc ("Modello Idrologico Semi-Distribuito in continuo"), mainly developed for flood simulation in Mediterranean basins, was tested on the Seveso Basin, which is stressed several times a year by flooding events mainly caused by excessive urbanization. The work summarizes a compendium of the MISDc applications over a wide range of catchments in European countries and then it analyses the performances over the Seveso basin. The results show a good fit behaviour during both the calibration and the validation periods with a NSE index larger than 0.9. Moreover, the median volume and peak discharge errors calculated on several flood events were less than 25%. In conclusion, we can assure that the reliability and computational speed could make the MISDc model suitable for flood estimation in many catchments of different geographical contexts and land use characteristics. Moreover, MISDc will be also useful for future support of real-time decision-making for flood risk management on the Seveso basin.