1,721,076 research outputs found
Linking the Kinetic Energy Fraction and Equivalent Length Method for Trickle Irrigation Design under Local Losses
No full textNew methods using analytical relationships to design drip irrigation laterals and subunits have been introduced in recent years based on the assumption that minor losses can be neglected. This assumption could be relaxed by applying the equivalent method, which makes it possible to account for minor losses, such as those caused by emitter connections, through formulas based on the rationale that an equivalent length of the drip lateral produces the same losses. However, equivalent length formulas are empirical; thus, they do not necessarily cover the entire range of conditions in the real-world contexts in which the formulas will be applied, and their extrapolation could lead to erroneous results. In this paper, theoretical equivalent lengths were calculated and linked to the kinetic energy fraction, which was considered as an alternative general procedure to compute minor losses. Therefore, the results obtained here are valid in all general contexts, because they were not affected by experimental calibrations. A methodology was suggested that extends the use of analytical relationships to design drip laterals from a previous method that neglects minor losses to a new method in which minor losses are considered. Several applications were performed for drip laterals in horizontal and in sloping fields. Results showed the reliability of this new design procedure
SCS Curve Number and Green-Ampt Infiltration Models
No full textSoil Conservation Service curve number (SCS-CN) and Green-Ampt (GA) infiltration models are probably the most applied equations in practical hydrology to compute the amount of direct runoff from rainfall. Both models are very simple, require few parameters, and present drawbacks and advantages. The empirical CN model concentrates the infiltration effect in the curve number and in the so-called soil hydrological groups, which have been widely characterized for different soil types, land cover, and antecedent soil moisture conditions (ASMCs), although the latter was considered ambiguous, whereas soil hydrological characteristics, including ASMC, are taken into account for the simplified physically based GA model. The main advantage of the GA model is the temporal variation of the rainfall excess intensity, which is not considered in the CN model. In this paper, CN and GA models are jointly used in order to analytically establish relationships linking each other, so that the positive features of both models together can be taken into account for applications. It is shown that the suggested procedure makes it possible to move from one model to the other and vice versa, according to the derived equations linking the relative parameters. Constant rainfall intensity was assumed; therefore, the procedure is better aimed to its design purpose at the small basin scale, rather than to reproducing rainfall-runoff events. A comparison between the results obtained by applying the suggested analytical procedure with those numerically derived by other researchers for SCS temporal storm distribution is performed and discussed
Analytical Solution of the Richards Equation under Gravity-Driven Infiltration and Constant Rainfall Intensity
No full textIn the field of soil hydrology, the Richards equation is commonly used to model water flow in unsaturated soils. The high nonlinearity of the Richards equation makes it very challenging to solve analytically for situations that are meaningful in practical applications. In this paper, an exact and simple analytical solution of the Richards equation under gravity-driven infiltration and constant rainfall intensity is derived. First, the solution is presented under Torricelli's law, which mimics the soil hydraulic conductivity function and describes the emptying or filling process of a nonlinear water reservoir. Then, following a similar approach, the solution is extended to the Brooks and Corey soil hydraulic conductivity function, which is generally considered to well describe soil hydrological characteristics. The approach followed in this study is a simple hydraulic approach; therefore, the derived solutions are not affected by uncertainty as long as the hypothesis of the gravity-driven infiltration is satisfied for the selected soils. A comparison with the solution numerically derived by the Richards equation for which the gravity-driven assumption is relaxed is performed and discussed. Interestingly, the comparison indicated that the suggested solution delimits the solutions domain of the Richards equation
Discussion of "Hydraulic Model of Transition of Transient to Steady Flows in the Vadose Zone" by Yaguo Zhang, Tonglu Li, Wei Shen, and Yu Wang
No full textThe authors wrote an interesting article dealing with a simple hydraulic model to illustrate the transition mechanism of transient to steady flows in the vadose zone. The soil behavior is described by a set of nine vertically aligned cylinders, each opened at the top and with a small outlet at the bottom. The water level dynamic of each cylinder, associated with an intermittent constant rainfall applied to the top cylinder, C0, was analyzed and numerical simulations were performed.
The only objective of this discussion is to show that results similar to those proposed by the authors could be obtained by using the recently introduced Richards equation analytical solution, under gravity-driven infiltration, and the Brooks and Corey (BC) hydraulic conductivity function (Baiamonte 2020a). Indeed, before applying the BC hydraulic conductivity function, for just one water tank, the previous solution was first introduced by studying the theoretical soil behavior under Torricelli’s law, as by the authors.
In this discussion, we will first briefly summarize the aforementioned solution for constant rainfall intensity and apply the solution for different parameters, including those considered in the original article. Then, the solution is extended to variable inflow intensity applied to the top of each cylinder. The analysis is performed for dimensionless groups, which make results more general than by using dimensional variables as in Zhang et al. (2019). Indeed, what makes them most useful is their ability to contract, or make more succinct, the functional form of physical relationships that are characterized by fewer dimensionless parameters
Variability of near-surface saturated hydraulic conductivity for the clay soils of a small Sicilian basin
No full textProper characterization of saturated hydraulic conductivity, Ks, of clay soils in a hillslope or a basin is still a challenge for soil science. In this investigation, the clay soils of the Maganoce (Sicily, Italy) basin were sampled at 19 sampling sites by the BEST procedure of soil hydraulic characterization. More OM implied less compact conditions (decreasing dry soil bulk density; coefficient of determination, R2 = 0.67), more stability to water of the soil aggregates (increasing water stable aggregates; R2 = 0.83) and, consequently, higher Ks values (R2 = 0.54). Variability of Ks was lower in the steeper zones of the basin than in the flatter ones. A comparison with the Ks data collected in the past with the Simplified Falling Head (SFH) technique at the same sampling points revealed a similarity between the two datasets but also a tendency of this last technique to yield some small Ks values that were not obtained with BEST. Soil disturbance due to ring insertion that SFH requires and/or Ks anisotropy likely contributed to explain this result. In conclusion, organic matter content and topographic attributes can help to plan an effective clay soil sampling strategy. High Ks values are expected to be less uncertain than small values
Biodiversità vegetale degli stagni temporanei della Sicilia
No full textGli ambienti umidi effimeri ospitano comunità vegetali specializzate e sono sede esclusiva di rare microterofite nonché autentiche stazioni di rifugio per molte specie a ciclo effimero. Per l’interesse bio-ecologico, Braun-Blanquet ha definito queste fitocenosi un gioiello floristico. Anche la Comunità Europea, con la direttiva Habitat 92/43/CEE, riconosce agli stagni temporanei mediterranei una notevole importanza e li individua come habitat prioritario (3170*).
Questi ambienti, essendo stagionali, di modesta estensione, spazialmente dispersi e difficilmente cartografabili, spesso vengono trascurati negli studi a scala di paesaggio. Tali habitat, invece, rappresentano veri e propri micro-hotsposts di biodiversità che contribuiscono in maniera significativa alla funzionalità ecosistemica e svolgono un ruolo fondamentale nelle dinamiche che controllano la connettività del mosaico territoriale.
In questo contributo vengono presentate caratteristiche vegetazionali, distribuzione nonché informazioni sullo stato di conservazione delle zone umide temporanee presenti in Sicilia.
Le fitocenosi analizzate sono riferite, dal punto di vista fitosociologico, alla classe Isoeto-Nanojuncetea, che nell’area di studio è rappresentata da cinque alleanze, per un totale di diciotto associazioni.
Questi biotopi peculiari ospitano specie poco comuni e di grande interesse fitogeografico come Myosusrus minimus, Isoetes velata, Damasonium polyspermum, Cicendia filiformis, Elatine gussonei, Isolepis cernua, Molineriella minuta, Sisymbriella dentata, Ranunculus parviflorus, Juncus capitatus, Crassula vaillantii
Geostatistical analisys on the relationship between vegetation pattern and human impact
No full textThe purpose of this work is to evaluate the vegetation pattern of a mediterranean landscape, analyzed through the shape of the patches that constitute it, and its relationship with alterations introduced by land use and human impact.
As a case of study the territory of the Monti Madonie Regional Park has been chosen, since it is a very heterogeneous area from the ecological point of view and a biodiversity hotspot.
Shape Index has been used to evaluate pattern geometry and has been calculated for every single polygon. Resulting data has been grouped by vegetation type. Value is 1 when the patch is maximally compact and increases as patch shape becomes more irregular. Geostatistical analysis has been performed on each dataset.
Acidophilous beech woods (Anemono apenninae-Fagetum) have the highest mean value (2,6), while basiphilous beech woods (Luzulo siculae-Fagetum) have a lower but still very high value (2,22). Basiphilous holm oak woods (Aceri campestris-Quercetum ilicis) show one of the highest mean values (2,43), while acidophilous holm oak woods (Geranio versicoloris-Quercetum ilicis, Teucrio siculi-Quercetum ilicis) value is lower (2,12). Even high mountain grasslands (Cerastio-Astragalion nebrodensis), serially connected to holm oak woods, show high values (2,18). Cliff vegetation (Asperulo-Potentilletum nebrodensis, Scabioso creticae-Centauretum ucriae, Anthemido cupanianae-Centauretum busambarensis) has an high value (ranging from 2,13 to 2,28) which is exclusively due to the abrupt change in slope. Thermophilous woods (IIici aquifoliae-Quercetum congestae, Oleo-Quercetum virgilianae, Quercetum leptobalanae, Erico-Quercion ilicis) have a mean value of 2,13. Grasslands and scrubs have intermediate values ranging from 1,97 to 2,03. Crops, vineyards and orange plantations have the lowest values, ranging from 1,49 to 1,82.
Geostatistical analysis demonstrated a clear relationship between vegetation pattern and land use. In agricultural areas human impact produces more regualr patch shapes (low shape index value) due to cadastral limits.
In natural and seminatural areas zonal vegetation shows a correlation between human impact and shape index values; in particular, woods which have been strongly exploited have higher shape index values. Azonal vegetation’s shape index value, instead, is exclusively correlated to terrain morphology
Land mosaic naturalness evaluation: a proposal for European landscapes
No full textThe present work proposes a criterion to classify landscape into naturalness systems using four levels of conservation: High naturalness, Semi-natural, Agricultural, Artificial. As a case study Sicily (Italy) was chosen. The methodology has been applied to reclassify Corine Land Cover data and obtain a Naturalness map. The area of study has been divided into reference units; these land units are the result of the overlay of the bioclimatic map and of the geomorphologic map. A new index to evaluate landscape naturalness and conservation is proposed, which has been calculated for each land unit. The highest value is located on the Nebrodi Mountains, a Regional Park where extensive beech woods are present and human activities are restricted. Very high values are correspondent to Mount Etna land systems (another Regional Park), the Ficuzza area and the Madonie Mountains (yet another Regional Park and a biodiversity hotspot). As expected, lowest values correspond to extensive urban areas and to industrial complexes. Agricultural landscape, widespread in Sicily, is almost always present in those land units whose values are in the mid-low range. The index has proved to be very useful for visualising the state of conservation and giving a general idea of human activity; it has been tested on Sicily, but could be applied to the entire European territory
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