Common-reflection-surface imaging of shallow and ultrashallow reflectors

We analyzed the feasibility of the common-reflection-surface (CRS) stack for near-surface surveys as an alternative to the conventional common midpoint (CMP) stacking procedure. The data-driven, less user-interactive CRS method could be more cost efficient for shallow surveys, where the high sensitivity to velocity analysis makes data processing a critical step. We compared the results for two field data sets collected to image shallow and ultrashallow reflectors: an example of shallow Pwave reflection for targets in the first few hundred meters, and an example of SH-wave reflection for targets in the first 10 m. By processing the shallow P-wave records using the CMP method, we imaged several nearly horizontal reflectors with onsets from 60 to about 250 ms. The CRS stack produced a stacked section more suited for a subsurface interpretation, without any preliminary formal and time-consuming velocity analysis, because the imaged reflectors possessed greater coherency and lateral continuity. With CMP processing of the SHwave records, we imaged a dipping bedrock interface below four horizontal reflectors in unconsolidated, very low velocity sediments. The vertical and lateral resolution was very high, despite the very shallow depth: the image showed the pinchout of two layers at less than 10 m depth. The numerous traces used by the CRS stack improved the continuity of the shallowest reflector, but the deepest overburden reflectors appear unresolved, with not well-imaged pinchouts. Using the kinematic wavefield attributes determined for each stacking operation, we retrieved velocity fields fitting the stacking velocities we had estimated in the CMP processing. The use of CRS stack could be a significant step ahead to increase the acceptance of the seismic reflection method as a routine investigation method in shallow and ultrashallow seismics

EHSMu: a New Ecohydrological Streamflow Model to Estimate Runoff in Urban Areas

A conceptual lumped ecohydrological streamflow model (EHSMu) is presented as a promising tool to simulate runoff in urban catchments. The model, based on the interaction between a soil bucket and two linear reservoirs, enables also evapotranspiration and aquifer recharge to be estimated. Notwithstanding its minimalism, EHSMu describes interactions among soil moisture dynamics, hydrological fluxes and ecological processes. The model was calibrated and validated within two densely urbanized sub-basins in Charlotte (US). A Monte Carlo procedure is used to investigate the efficiency of random sets of 8 model parameters. Results show the high model performance (NSE = 0.72). The influence of land use change is evaluated, by varying the imperviousness and crop coefficients. Synthetic experiments show that increasing urbanization triggers a linear decrease in evapotranspiration and aquifer recharge, while it increases the fast runoff. An opposite response is achieved by installing vegetation with higher potential evapotranspiration, which would contribute to the actual evapotranspiration making up 50–55% of the total water balance

Awareness and willingness to pay for green roofs in Mediterranean areas

Green roofs have been extensively investigated in recent years, showing that their implementation in urban areas provides multiple benefits (e.g., pluvial flood mitigation, urban heat island reduction, energy saving, increase of biodiversity, CO2 sequestration) and supports sustainable urban development. Although green roof benefits have been widely recognized, the perception that the community has of these nature-based solutions and the willingness to pay for their installation in urban areas is still not clear nor quantified. Societal perception and willingness to pay for green roofs are fundamental for urban planners and decision makers, since they represent the community participation in the sustainable development of urban areas. In this work, we aim to analyze how citizens perceive green roofs and how willing they are to pay for the installation and maintenance of these nature-based solutions. We used an online survey to investigate the perception and the knowledge of green roofs as a potential solution to common environmental issues (i.e., urban flood, increase of temperature, energy consumption, air pollution and lack of green spaces), and the interest and willingness to pay for green roof installation on both public and private roofs. Based on the answers of 389 respondents living in Sardinia (Italy), our analysis revealed that most citizens are aware of what green roofs are, and they are aware that, although these nature-based solutions can not completely solve environmental issues, they can greatly contribute to the mitigation of these phenomena. Results also show a higher interest in the installation of green roofs on public buildings than on private ones, due to the high installation costs. Moreover, for private roofs, the possibility to install photovoltaic panels instead of GRs is generally preferred. Most of the respondents are willing to spend less than 100 € per year for the maintenance of green roofs on public buildings and to invest less than 5000 € for the installation on their own house

The role of green roofs in urban Water-Energy-Food-Ecosystem nexus: a review

Green roofs are strategic tools that can play a significant role in the creation of sustainable and resilient cities. They have been largely investigated thanks to their high retention capacity, which can be a valid support to mitigate the pluvial flood risk and to increase the building thermal insulation, ensuring energy saving. Moreover, green roofs contribute to restoring vegetation in the urban environment, increasing the biodiversity and adding aesthetic value to the city. The new generation of multilayer green roofs present an additional layer with respect to traditional ones, which allows rainwater to be stored, which, if properly treated, can be reused for different purposes. This paper offers a review of benefits and limitations of green roofs, with a focus on multilayer ones, within a Water-Energy-Food-Ecosystem nexus context. This approach enables the potential impact of green roofs on the different sectors to be highlighted, investigating also the interactions and interconnections among the fields. Moreover, the Water-Energy-Food-Ecosystem nexus approach highlights how the installation of traditional and multilayer green roofs in urban areas contributes to the Development Goals defined by the 2030 Sustainable Agenda

Inversion of electrical conductivity data with Tikhonov regularization approach: some considerations

Electromagnetic induction measurements, which are generally used to determine lateral variations of apparent electrical conductivity, can provide quantitative estimates of the subsurface conductivity at different depths. Quantitative inference about the Earth’s interior from experimental data is, however, an ill-posed problem. Using the generalised McNeill’s theory for the EM38 ground conductivity meter, we generated synthetic apparent conductivity curves (input data vector) simulating measurements at different heights above the soil surface. The electrical conductivity profile (the Earth model) was then estimated solving a least squares problem with Tikhonov regularization optimised with a projected conjugate gradient algorithm. Although the Tikhonov approach improves the conditioning of the resulting linear system, profile reconstruction can be surprisingly far from the desired true one. On the contrary, the projected conjugate gradient provided the best solution without any explicit regularization (a = 0) of the objective function of the least squares problem. Also, if the initial guess belongs to the image of the system matrix, Im(A), we found that it provides a unique solution in the same subspace Im(A)

Physical controls on the scale-dependence of ensemble streamflow forecast dispersion

Abstract. The accuracy of ensemble streamflow forecasts (ESFs) is impacted by the propagation of uncertainty associated with quantitative precipitation forecasts (QPFs) through the physical processes occurring in the basin. In this study, we consider consistent ESFs (i.e., observations and ensemble members are equally likely) and we study the effect of basin area (A) and antecedent rainfall (AR) on the ESF dispersion, a metric of flood forecast skill. Results from a set of numerical experiments indicate that: (i) for small basins (≲180 km2), ESF dispersion is mainly dominated by the runoff generation process and does not depend on the basin size A; (ii) for larger areas, ESF dispersion decreases with A according to a log-linear relation due to the decreasing variability of ensemble QPFs and, possibly, to the channel routing process. In addition, we found that, regardless the basin size, the ESF dispersion decreases as AR increases, and that the influence of AR is larger for basins with fast response times. Physical controls (land cover, soil texture and morphometric features) on the analyzed basin response confirm these interpretations

Management strategies for maximizing the ecohydrological benefits of multilayer blue-green roofs in mediterranean urban areas

Multilayer Blue-Green Roofs are powerful nature-based solutions that can contribute to the creation of smart and resilient cities. These tools combine the retention capacity of traditional green roofs with the water storage of a rainwater harvesting tank. The additional storage layer enables to accumulate the rainwater percolating from the soil layer, that, if properly treated, can be reused for domestic purposes. Here, we explore the behavior of a Multilayer Blue-Green Roof prototype installed in Cagliari (Italy) in 2019, that have been equipped with a remotely controlled gate to regulate the storage capacity of the system. The gate installation allows to manage the Multilayer Blue-Green Roof in order to increase the flood mitigation capacity, minimizing the water stress for vegetation and limiting the roof load with adequate management practices. In this work, 10 rules for the management of the Multilayer Blue-Green Roof gate have been investigated and their performances in achieving different management goals (i.e., mitigating urban flood, increasing water storage and limiting roof load on the building) have been evaluated, with the aim to identify the most efficient approach to maximize the benefits of this nature based solution. An ecohydrological model have been calibrated based on field measurements carried out for 6 months. The model has been used to simulate the system performance in achieving the proposed goals, using as input nowdays and future rainfall and temperature time series. The analysis reveled the importance of the correct management of the gate, highthing how choosing and applying a specific management rule helps increasing the performance in reaching the desired goal

Design and construction of earth dams.

This thesis deals with the design and construction of rolled-fill earth dams with the standard methods of practice, taking the Hirakud Dam as the basis. The field operations of the investigation to obtain observational information and to secure samples for the laboratory testing include observation of rain gauge and river gauge readings, taking river water samples, digging test pits, drilling grout holes, opening drifts, digging borrow pits and conducting detailed topographical surveys. Laboratory tests are conducted on the samples and the results are plotted in graphs. Rainfall and run-off statistics are plotted in graphs. Observational information of geology is plotted in log sheets and the field data of survey works is made use of for the preparation of the topographical maps. From the results of the investigation it is found that the Hirakud Dam has a firm foundation and there is sufficient quantity of material for the embankment at site. The annual rainfall is 47.49 inches yielding a run-off of 50 million sore feet over a catchment area of 32,200 square miles. The stability of the embankment is computed by the slip circle method and the seepage water from the flow net method. The dam is designed for 100 years with a reservoir capacity of 5.98 million acre feet at the maximum water level elevation 625 feet, the bed level being elevation 500 feet. The dead storage is 2.24 million acre feet corresponding to elevation 590 feet, and the maximum submerged area corresponding elevation 625 feet is 150,380 acres. The minimum factor of safety for the upstream slope is 1.68 and that for the downstream slope is 1.19. The seepage water is 0.264 cubic feet per lineal foot per year. The dam is to be constructed as per the design and the specifications. The compaction is attained by the mechanical effort at the optimum moisture content. The mechanical effort is influenced by the type of roller, its weight and the number of passes. Field control is affected by vigilant supervision, needle penetration, ring test and sand test. The construction is to be carried out according to a plan of seven stages. A comparison and contrast is drawn between the U.S.A. and India to bring out the inherent difficulties of construction operations of large dams in India. Importance is given to the sequence of the subject matter since no text book gives all the relevant portions as used in practice. Reference is given to the text books from which the formulas are taken so that a student who is interested in theory, derivation and explanation of the formulas may study the available literature. The procedures employed and the conclusions drawn are based on the experience, observation and the research study of the author both in India and the United States of America

Inversion of electrical conductivity data with Tikhonov regularization approach: some considerations

Electromagnetic induction measurements, which are generally used to determine lateral variations of apparent electrical conductivity, can provide quantitative estimates of the subsurface conductivity at different depths. Quantitative inference about the Earth's interior from experimental data is, however, an ill-posed problem. Using the generalised McNeill's theory for the EM38 ground conductivity meter, we generated synthetic apparent conductivity curves (input data vector) simulating measurements at different heights above the soil surface. The electrical conductivity profile (the Earth model) was then estimated solving a least squares problem with Tikhonov regularization optimised with a projected conjugate gradient algorithm. Although the Tikhonov approach improves the conditioning of the resulting linear system, profile reconstruction can be surprisingly far from the desired true one. On the contrary, the projected conjugate gradient provided the best solution without any explicit regularization ( a= 0) of the objective function of the least squares problem. Also, if the initial guess belongs to the image of the system matrix, Im(A), we found that it provides a unique solution in the same subspace Im(A)

Distributed hydrologic modeling of a sparsely monitored basin in Sardinia, Italy, through hydrometeorological downscaling

The water resources and hydrologic extremes in Mediterranean basins are heavily influenced by climate variability. Modeling these watersheds is difficult due to the complex nature of the hydrologic response as well as the sparseness of hydrometeorological observations. In this work, we present a strategy to calibrate a distributed hydrologic model, known as TIN-based Real-time Integrated Basin Simulator (tRIBS), in the Rio Mannu basin (RMB), a medium-sized watershed (472.5 km2) located in an agricultural area in Sardinia, Italy. In the RMB, precipitation, streamflow and meteorological data were collected within different historical periods and at diverse temporal resolutions. We designed two statistical tools for downscaling precipitation and potential evapotranspiration data to create the hourly, high-resolution forcing for the hydrologic model from daily records. Despite the presence of several sources of uncertainty in the observations and model parameterization, the use of the disaggregated forcing led to good calibration and validation performances for the tRIBS model, when daily discharge observations were available. The methodology proposed here can be also used to disaggregate outputs of climate models and conduct high-resolution hydrologic simulations with the goal of quantifying the impacts of climate change on water resources and the frequency of hydrologic extremes within medium-sized basins