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The pressure damping occurring in pressurized pipes with a leak during transients has been examined as a diagnostic tool – the so-called transient damping method (TDM) – mainly from the theoretical and numerical point of view. On the contrary, the experimental data are limited to few cases. As a consequence, there is a need of an extensive experimental analysis of the role played on the pressure damping by leak parameters (size, location and initial pressure). On the basis of the laboratory tests executed on a polymeric pipe, it is shown that, while the magnitude of the injected pressure wave does not affect the damping, the initial pressure, the leak size and location influence it plainly. Moreover, an experimental evidence is provided of the ambiguity in the time-domain of the transient pressure damping pointed out by numerical experiments. Precisely, it is demonstrated that different combinations of the leak parameters can lead to the same pressure damping. The obtained results indicate that the TDM can give a reliable assessment of the pipe status only if it is integrated with other diagnostic tools, such as the interpretation of the pressure signal during the first characteristic time of the pipe.

Determining "representative" rain gauge stations over a wide area is useful to optimize an existing rain gauge network, design a network in ungauged basins and calibrate a meteorological radar by ground measurements. Most available methodologies have been developed for specific watersheds and cannot be objectively transferred to other regions. This issue is addressed here through a reformulation of the temporal stability analysis for the areal-average cumulative rainfall depth, R, of single meteorological systems and an evaluation of its efficiency for application to common typologies of frontal systems with different physical characteristics. On this basis, our results suggest that, in each watershed, the combination of the measurements performed in the two stations with better ranking gives a fairly good representation of R derived from all the operative rain gauges, particularly for significant frontal systems, with the magnitude of the relative error generally less than 10%.

Intensity Duration Frequency (IDF) curves are important tools for hydraulic and hydrologic design. Considering that there are different approaches to obtain the rainfall quantiles on which the IDF curves are based, the availability of a method to evaluate their reliability is of great importance. With this aim, in this work the multifractal properties of hourly rainfall data recorded at 23 rain gauges in the Umbria Region (Italy) have been used to select the most appropriate frequency analysis method of extreme annual rainfall at each location. Three methods have been tested: Local Frequency Analysis (by fitting at each station extreme annual rainfall data of different durations by a probability distribution function), Regional Frequency Analysis approach based on L-Moments and flood index method (considering the extreme annual rainfall data from all the stations), and a variant of the latter method known as In-site Regional Frequency Analysis (based on the consideration of the station as a region). Therefore, quantiles of rainfall for different durations and return periods have been obtained. These quantiles have been fitted to the Montana Intensity-Duration-Frequency (IDF) curve. The scaling properties of rainfall have been obtained through out the empirical moments scaling function K(q). Their comparison with some scaling behavior properties of the IDF curves has let the selection of the most adequate quantile estimation method at each site, being the Regional Frequency Analysis the most appropriate one for 14 out of the 23 sites included in the study.

In this paper, the transient behavior of a single-branch pipe system (Y-system) is analyzed by means of numerical experiments in which a wide range of branch characteristics (i.e., size, lo...

The saturated hydraulic conductivity, Ks, is a soil property that has a key role in the partitioning of rainfall into surface runoff and infiltration. The commonly used instruments and methods for in situ measurements of Ks have frequently provided conflicting results. Comparison of Ks estimates obtained by three classical devices—namely, the double ring infiltrometer (DRI), the Guelph version of the constant-head well permeameter (GUELPH-CHP) and the CSIRO version of the tension permeameter (CSIRO-TP) is presented. A distinguishing feature in this study is the use of steady deep flow rates, obtained from controlled rainfall–runoff experiments, as benchmark values of Ks at local and field-plot scales, thereby enabling an assessment of these methods in reliably reproducing repeatable values and in their capability of determining plot-scale variation of Ks. We find that the DRI grossly overestimates Ks, the GUELPH-CHP gives conflicting estimates of Ks with substantial overestimation in laboratory experiments and underestimation at the plot scale, whereas the CSIRO-TP yields average Ks values with significant errors of 24% in the plot scale experiment and 66% in laboratory experiments. Although the DRI would likely yield a better estimate of the nature of variability than the GUELPH-CHP and CSIRO-TP, a separate calibration may be warranted to correct for the overestimation of Ks values. The reasons for such discrepancies within and between the measurement methods are not yet fully understood and serve as motivation for future work to better characterize the uncertainty associated with individual measurements of Ks using these methods and the characterization of field scale variability from multiple local measurements.

The subsea transmission main (TM) of Trieste, Italy, plays a crucial role in the water supply system managed by AcegasApsAmga SpA (Hera Group). With the aim of implementing a systematic inspection procedure (at present divers are used for periodic surveys) AcegasApsAmga SpA decided to proceed with Transient Test-Based Techniques (TTBTs). In this paper, the results of preliminary transient tests generated by means of the existing devices (the first option to be considered within TTBTs) are discussed and possible alternatives are highlighted.

Even though natural surfaces are rarely horizontal, infiltration modeling has been primarily confined to horizontal surfaces, and there are not enough studies to clarify the effects of slope on the partition of rainfall into surface and subsurface water. Besides, previous experimental results on the effects of slope provide conflicting conclusions perhaps because of the existence of erosion and crust formation. In this study, new laboratory experiments, performed in the absence of the last two processes, highlight the effect of the slope angle, γ, on infiltration into a grassy soil. The results are compared with those from previous experiments performed on a bare soil and interpreted in terms of an effective soil saturated hydraulic conductivity, Ke (γ). The grassy soil dampens the variation of Ke with γ compared to bare soil. For example, for γ = 10°, the reduction of the gravitational infiltration with respect to the saturation condition was ∼80% for the bare soil, while we find it to be ∼20% for the grassy soil. Finally, we point out that the presence of grass does not affect the results through the development of a two layered soil, but through a substantial variation of roughness.

In recent years there is a growing concern by the community, scientific and not, about global warming and climate changes. The fact that the global temperature is growing up after the increase of the greenhouse gases emissions is already known, but there is still wondering about its effect on the hydrological cycle and most of all, on rainfalls. Many studies supported by the Intergovernmental Panel on Climate Change (IPCC) showed that there is a general increase of heavy rainfalls also in areas where total annual precipitation is not prominently changed. Changings about frequency, intensity, duration in rainfalls and in weather events in general are still objects of uncertainty and past studies referred to different regions do not give an unanimous answer about their trends. The Mediterranean area, which includes Italy, is supposed to be one of the most reactive to climate change and deep effects are expected. This paper deals with rainfall tendencies in the Umbria Region, Central Italy, since almost all the regional territory is included in the Upper Tiber River Basin and many areas are prone to risk of flooding. The climate in the Umbria region is different from zone to zone, in fact the weather is cold and wet in the East areas, near the Apennine Mountains and hotter and drier in the West, close to Tuscany region. Because of this variability a lot of rain gauges were placed in the last 10-15 years. Nowadays a very dense rain gauge network is present (more than 90 rain gauges for a regional area of 8464.33 km 2 , about one station each 90 km 2 ). The aim of this paper is to analyze if climate change affects rainfall intensity in Umbria. Three meteorological stations have been selected: Citta di Castello, Todi and Orvieto. They provide the longest series of data and the best quality in rainfall measurements. Rainfall measurements began in the thirties and have gone on until nowadays even if there are some interruptions (most of all during the years of the Second World War). The analyses of heavy rainfalls of the three stations, and most of all the data referred to Todi, whose geographical position is barycentric in the regional territory; show that there are not considerable changes in rainfall maxima and intensities in the last seventy years.

For a few decades the local rainfall measurements are generally obtained by tipping bucket sensors, that allow to record each tipping time corresponding to a well-known rain depth. However, a considerable part of rainfall data to be used in the hydrological practice is available in aggregated form within constant time intervals. This can produce undesirable effects, like the underestimation of the annual maximum rainfall depth, Hd, associated with a given duration, d, that is the basic quantity in the development of rainfall depth-duration-frequency relationships. The errors in the evaluation of Hd from data characterized by a coarse temporal aggregation, ta, and a procedure to reduce the non-homogeneity of the Hd series are here investigated. Our results show that for ta = 1 min the underestimation is practically negligible, whereas for larger temporal aggregations with d = ta the error in a single Hd can reach values up to 50% and in a series of Hd in the average up to 17%. Relationships between the non-dimensional ratio ta/d and the average underestimation of Hd, derived through continuous rainfall data observed in many stations of Central Italy, are presented to overcome this issue. These equations allow to improve the Hd estimates and the associated depth-duration-frequency curves at least in areas with similar climatic conditions. The effect of the correction of the Hd series on the rainfall depth-duration-frequency curves is quantified. Our results indicate that the improvements obtained by the proposed procedure are of the order of 10%.

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, Q d , 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 Q d ( γ = 1 °) / Q d ( 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.

Summary Infiltration on sloping surfaces occupies an important role in our understanding of surface and subsurface hydrology. Previous studies have provided conflicting results about the role of slope on infiltration. Here, our main objective is to highlight, by well-controlled experiments, the slope role in the absence of the conflicting contributions generated by other physical processes observed in previous studies under natural or laboratory conditions. The experimental program was designed to resolve some of the confounding factors such as lower impermeable boundary condition, range of rainfall rates relative to soil saturated hydraulic conductivity, surface sealing, and erosion of top soil. The experimental apparatus consists of a box containing a natural bare soil with slope angle γ chosen between 0° and 10°, two sensors of surface and deep flow, one probe for moisture content and an artificial rainfall generator. The primary experimental results suggest that under steady conditions and rainfall rate, r, greater than saturated hydraulic conductivity, Ks, the deep flow, Qd, decreases with increasing slope angle, γ, up to a value leading to Qd(γ = 1°)/Qd(γ = 10°) equal to ≈4 which is in contrast with the results provided in a few earlier papers. Furthermore, in sloping bare soils surface runoff is produced even for r