Root reinforcement and slope bioengineering stabilization by Spanish Broom (<i>Spartium junceum</i> L.)

The present paper deals with the root system's characteristics of Spanish Broom (<i>Spartium junceum</i> L.), a species whose capacity for adaptating and resisting to drought is worth investigating. In particular, the aims of the study were 1) to investigate the plant's bio-mechanical aspects and 2) to verify whether root reinforcement and the field rooting ability of stem cuttings enhance its potential for use in slope stabilization and soil bio-engineering techniques, particularly in the Mediterranean areas. <br><br> Single root specimens were sampled and tested for tensile strength, obtaining classic tensile strength-diameter relationships. Analysis were performed on the root systems in order to assess root density distribution. The Root Area Ratio (RAR) was analyzed by taking both direct and indirect measurements, the latter relying on image processing. The data obtained were used to analyze the stability of an artificial slope (landfill) and the root reinforcement. The measurement and calculation of mean root number, mean root diameter, RAR, root cohesion and Factor of safety are presented in order to distinguish the effect of plant origin and propagation. <br><br> Furthermore, tests were performed to assess the possibility of agamic propagation (survival rate of root-ball endowed plants, rooting from stem cuttings). These tests confirmed that agamic propagation is difficult, even though roots were produced from some buried stems, and for practical purposes it has been ruled out. <br><br> Our results show that Spanish Broom has good bio-mechanical characteristics with regard to slope stabilization, even in critical pedoclimatic conditions and where inclinations are quite steep, and it is effective on soil depths up to about 50 cm, in agreement with other studies on Mediterranean species. It is effective in slope stabilization, but less suitable for soil bio-engineering or for triggering natural plant succession

Runoff generation processes in a Mediterranean research catchment (Sardinia)

In recent decades the hydrological community has increasingly improved its understanding of the runoff generation in river basins. Since Horton (1933), numerous studies have investigated these mechanisms at the plot, hillslope and catchment scale (e.g.: Betson, 1964; Dunne and Black, 1970; Pilgrim et al., 1978; Kirkby, 1978; Mosley, 1979; Beven, 1989; Anderson and Burt, 1991). The primary processes that have been observed and described to explain runoff generation in a catchment area are: (1) Hortonian Overland Flow (HOF), which occurs when rainfall intensity exceeds the infiltration capacity of the soil; (2) Saturation Overland Flow (SOF), which occurs when the storage capacity of the soil is exceeded and defines the concept of contributing saturated areas, which expand as rainfall volume increases; Saturated Subsurface Flow (SSF), which occurs when the water in the soil flows along lateral paths and thus contributes to streamflow as return flow from the groundwater aquifer.</br

Evaporation in a Mediterranean environment by energy budget and Penman methods, Lake Baratz, Sardinia, Italy

Abstract. In Mediterranean environments, evaporation is a key component of lake water budgets. This applies to Lake Baratz in Sardinia, Italy, a closed lake that almost dried up in 2008 after a succession of years with low seasonal rainfall. We used the energy budget method and Penman's equation to estimate evaporation over Lake Baratz. We measured, using a raft station, water temperature at the surface, at 1, 2, 4, 6 m depth and at the bottom of the lake, as well as air temperature, relative humidity, wind speed, and net radiation over a period of 3 years. We also compared Penman's equation and the energy budget method in two other climatic zones using published data. Our results indicate that mean yearly evaporation over Lake Baratz was 950 mm. On an annual scale, evaporation estimated by Penman's method omitting heat storage as is usually done was 18% higher than by the energy budget method that included heat storage, with monthly differences ranging between −38 and +60%. Including the heat storage term in Penman's equation changed the monthly values but did not change the yearly value significantly. Solar radiation and heat storage were found to be the most important energy fluxes to and from the lake and had the greatest effect on evaporation rates for the energy budget method. The bias between the two methods has a seasonal cycle due to the storage and release of energy from the lake. Energy advected to and from the lake by precipitation, surface water and ground water had minor effect on evaporation rates. Lake Baratz, like other lakes in a Mediterranean environment, is particularly sensitive to the summer hot and dry climate. In contrast, we found that rates of evaporation estimated from Penman and the energy budget methods over tropical African lakes were nearly constant over the entire year and the difference between the two methods smaller. Difference between the two methods for North American lakes is also smaller probably owing to the ice-cover season and to lower radiation and lower temperatures during summer

Comparing the Hydraulic Properties of Forested and Grassed Soils on an Experimental Hillslope in a Mediterranean Environment

AbstractThis experimental research compares the physical and hydraulic properties of two adjacent soils, one covered with a native forest of Mediterranean maquis, and the other with spontaneous grass. The latter replaced the previous natural forest. The aim is to quantify the significant differences in the soil properties caused by the removal of the natural vegetation. Although the soil texture was similar in the different land uses, the soil under the forest had a higher organic matter content, a lower apparent density and a higher water content at saturation than the grassed soil. The analysis of the water retention characteristics indicated that the retained water content of the forest soil exceeded that of the grassed soil in the range from saturation to -50cm of water tension. This suggests that changing the land use altered the soil pore structure within this range. The hydraulic conductivity of the forest soil exceeded that of the grassed soil at water tensions of -10, -5 and -3cm. Conversely the hydraulic conductivity of the grassed soil was similar to that of the forest soil at -1cm of water tension and at saturation. This result was probably due to the hydraulic activation of the desiccation cracks in the grassed soil. This increased the amount of infiltrated water in saturated and near-saturated soil conditions.This work shows that changes in land use have an unfavorable impact on the physical and hydraulic properties of the soil. Soil covered with grass is more vulnerability to water erosion than that under forest, and there is likely to be general worsening of flow regimes

SCHEMA SPERIMENTALE PER LA STIMA DELLA CONDUCIBILITÀ IDRAULICA LATERALE ALLA SCALA DI VERSANTE

La conducibilità idraulica alla saturazione, KS, è un parametro fondamentale per la simulazione del flusso idrico nel suolo. La memoria illustra un approccio sperimentale per la stima della KS laterale alla scala di versante. La metodologia proposta è stata applicata in due aree contigue ricoperte, rispettivamente, da macchia mediterranea e prato. Sono stati registrati i livelli di falda e i deflussi idrici sottosuperficiali, e queste misure sono state usate per il calcolo della KS del suolo tramite l’equazione di Darcy. Il monitoraggio è stato effettuato durante il periodo piovoso compreso tra gennaio e giugno 2014. In aprile, inoltre, sono state eseguite prove di pioggia artificiale con intensità di 30 e 70 mm h-1. Durante le precipitazioni naturali, il valore massimo di KS stimato nel prato è stato di 2870 mm h-1, mentre è stato pari a 2400 mm h-1 nel corso delle prove di saturazione artificiale. Il valore massimo di KS pari 4000 mm h-1 è stato ottenuto, nella macchia, durante le prove di pioggia artificiale. Per contro, valori minori di KS sono stati ottenuti durante le piogge naturali a causa delle basse portate sottosuperficiali registrate. La metodologia proposta è risultata idonea per la stima di valori della conducibilità idraulica rappresentativi per le aree di interesse. Tali informazioni potranno garantire una maggiore attendibilità della modellizzazione dei processi idrologici a scala di versante e di bacino

glmGUI v1.0: an R-based graphical user interface and toolbox for GLM (General Lake Model) simulations

Abstract. Numerical modeling provides an opportunity to quantify the reaction of lakes to alterations in their environment, such as changes in climate or hydrological conditions. The one-dimensional hydrodynamic General Lake Model (GLM) is an open-source software and widely used within the limnological research community. Nevertheless, no interface to process the input data and run the model and no tools for an automatic parameter calibration yet exist. Hence, we developed glmGUI, a graphical user interface (GUI) including a toolbox for an autocalibration, parameter sensitivity analysis, and several plot options. The tool is provided as a package for the freely available scientific code language R. The model parameters can be analyzed and calibrated for the simulation output variables water temperature and lake level. The glmGUI package is tested for two sites (lake Ammersee, Germany, and lake Baratz, Italy), distinguishing size, mixing regime, hydrology of the catchment area (i.e., the number of inflows and their runoff seasonality), and climatic conditions. A robust simulation of water temperature for both lakes (Ammersee: RMSE =1.17 ∘C; Baratz: RMSE =1.30 ∘C) is achieved by a quick automatic calibration. The quality of a water temperature simulation can be assessed immediately by means of a difference plot provided by glmGUI, which displays the distribution of the spatial (vertical) and temporal deviations. The calibration of the lake-level simulations of lake Ammersee for multiple hydrological inputs including also unknown inflows yielded a satisfactory model fit (RMSE =0.20 m). This shows that GLM can also be used to estimate the water balance of lakes correctly. The tools provided by glmGUI enable a less time-consuming and simplified parameter optimization within the calibration process. Due to this, i.e., the free availability and the implementation in a GUI, the presented R package expands the application of GLM to a broader field of lake modeling research and even beyond limnological experts

Shallow landslide disposition in burnt European beech (Fagus sylvatica L.) forests

Tree roots contribute significantly to soil strength on hillslopes. In the case of wildfires, this effect may abruptly vanish and be lacking for a considerable period of time depending on the resistance and resilience of the forest. Despite its importance, quantitative data on the impact and dynamics of wildfires on slope stabilization is still lacking. We use the study case of the Fagus sylvatica L. to quantify the medium-term evolution of root reinforcement and its effect on slope stability in fire-injured forests. In the study, we upscale root reinforcement using field data for the calibration of the Root Bundle Model and detailed information on forest structure in 244 plots, and calculate the spatio-temporal dynamics of forest protective capacity using a three-dimensional probabilistic slope stability model (slideforNET) for different site types. In unburnt and low-burn forests, the protective capacity was found to remain constant over time. Forests hit by moderate burns continue to provide adequate protection for shallow (depth < 0.5 m) and cohesive soils only, whereas in the case of high severity fires, the protective capacity vanishes for 15 years and an increased shallow landslide probability remains for at least 40 years. These conditions call for appropriate sylvicultural post-fire measures

The Open Data Kit suite, Mobile Data Collection technology as an opportunity for forest mensuration practices

This paper examines the potential for using Mobile Data Collection (MDC) as an effective database supported technology to substantially improve forest mensuration practices. Open source Open Data Kit (ODK) procedures and tools were used during a survey campaign that initiated a local forest monitoring process in the Marganai forest (Sardinia). The ODK suite is practical to use and its procedures allow authoring and use of digital survey forms without users needing software development expertise. Form design enables a high degree of customization to be achieved by means of specifying a wide range of data flow control mechanisms. ODK has proved to be a valid tool for data coherence and completeness improvements. As forestry’s contribution to regional Gross Domestic Product has dramatically decreased, forest mensuration practices have been reduced. Meeting the increased need to monitor environmental assets such as forests requires these practices to be re-evaluated. If regional public institutions took an active part in the process of enhancing forest mensuration, by contributing with open database systems acting as repositories and knowledge engines, support for MDC tools like ODK would potentially be a great opportunity to disseminate the use of the system and boost its development

Large-scale lateral saturated soil hydraulic conductivity as a metric for the connectivity of subsurface flow paths at hillslope scale

Lateral saturated soil hydraulic conductivity, Ks,l, is the soil property governing subsurface water transfer in hillslopes, and the key parameter in many numerical models simulating hydrological processes at the hillslope and catchment scales. Likewise, the hydrological connectivity of the lateral flow paths plays a significant role in determining the rate of the subsurface flow at various spatial scales. This study investigates the relationship between Ks,l and hydrological connectivity at the hillslope spatial scale. Ks,l was determined by the subsurface flow rates intercepted by drains and water table depths observed in a well network. The hydrological connectivity was evaluated by the synchronicity among water table peaks, and between these and the peaks of the drained flow. Rainfall and soil moisture were used to investigate the influence of the transient hydrological soil condition on connectivity and Ks,l. As the synchronicity of the water table response between wells increased, the lag times between the peaks of water levels and those of the drained subsurface flow decreased. Moreover, the most synchronic water table rises determined the highest drainage rates. The relationships between Ks,l and water table depths were highly non-linear, with a sharp increase in the values for water table levels close to the soil surface. Estimated Ks,l values for the full saturated soil were in the order of thousands of mm h−1, suggesting the activation of macropores in the root zone. The Ks,l values determined at the peak of the drainage events were correlated with the indicators of synchronicity. The sum of cumulative rainfall and antecedent soil moisture was correlated with the connectivity indicators and Ks,l. We suggest that, for simulating realistic processes at the hillslope scale, the hydrological connectivity could be implicitly considered in hydrological modelling through an evaluation of Ks,l at the same spatial scale