Giuseppe Bombino

Evaluation and modeling of scouring and sedimentation around check dams in a Mediterranean torrent in Calabria, Italy

The effectiveness of check dams on channel morphology of managed torrents is rarely assessed. Therefore, there is a need for studies that focus on the impacts of existing engineering check dams on the planoaltimetric characteristics of the torrent, particularly in Mediterranean areas, where the hydrological regime of ephemeral channels is dynamically unsteady. The quantitative evaluation of the effects of the check dams on channel morphology after many years (i.e., at least four or five decades) helps introduce innovations to the usual analysis of check dam efficacy which have often been limited to qualitative observations for only a few years after installation. As a contribution to make up these shortcomings, this paper investigates the geomorphologic asset of a torrent in southern Italy containing 10 check dams (installed in the 1950s to 1960s) and analyzes the dynamics of the scouring and sedimentation processes upstream and downstream of selected check dams after 8 rainfall events; moreover, the capability of the model by Castillo (2007) to predict scouring/sedimentation in proximity to these check dams is assessed. Sediment stored upstream of each check dam (where lower channel gradients and wider channel sections formed very long and wide sedimentary wedges) is more than one order of magnitude higher compared to scouring downstream. The morphological analysis revealed that the check dams installed in the headwater reach play a function of bed stabilization (due to the longitudinal slope reduction) and flood lamination (because of the wider channel section) rather than a role of sediment collectors as their sediment storage capacity has already been completed. Scouring/sedimentation dynamics depend mainly on the channel slope and width in proximity to the check dams rather than on structure height. Finally, Castillos model showed an acceptable performance in predicting scouring/sedimentation in the channel bed close to check dams after the monitored rainfall events, the model efficiency being satisfactory and the differences between the mean observed and simulated values low. This investigation improves the understanding about morphological effects of check dams in Mediterranean torrents based on field observations and quantitative analysis.

Depuration in aerated ponds of citrus processing wastewater with a high concentration of essential oils

Citrus processing wastewater was treated in aerated pilot plants in order to evaluate the following: (a) energy efficiency under different air flow rates and times; and (b) limits of spontaneous microflora in adapting to essential oils. In comparison to permanent air flow, night aeration for 12 hours determined an increase of up to 12% of the monthly removal rate of chemical oxygen demand (COD) and a consequent reduction by 10% of energy consumptions per unit of COD removed from 0.63 to 0.57 kWh/kgCOD. Lowering night aeration from 14 to 7 l/m3/h reduced by only 10% the removal rate of COD; the energy consumption per unit of COD removed (0.32 kWh/kgCOD) was consequently reduced by more than 40%. Dissolved oxygen was maintained at very low level, rarely exceeding 0.2 ppm, with no bad smell. The consequent high oxygen deficit of 98–99% of saturation induced high oxygen transfer efficiency. The microbial population was characterized mainly by aerobic bacteria; only 5–8% of bacteria were strictly anaerobic. In the deep tank layer under the air diffuser a small amount of sludge settled (0.03–0.04 kg of dry matter per kg of COD removed), containing only 3% of total organic matter detected at the end of the depuration process. The fact that the concentration of essential oils could be progressively increased up to 1400 ppm without noticeably slowing down the biological processes demonstrated the remarkable microbial adaptation.

Adjustments in channel morphology due to land‐use changes and check dam installation in mountain torrents of Calabria (southern Italy)

In Mediterranean semi-arid conditions, the availability of studies monitoring channel adjustments as a response to reforestation and check dams over representative observation periods, could help develop new management strategies. This investigation is an integrated approach assessing the adjustments of channel morphology in a typical torrent of southern Italy after land-use changes and check dam construction across a period of about 60 years. A statistical analysis of historical rainfall records, an analysis of land-use changes in the catchment area and a geomorphological mapping of channel adjustments were carried out and combined with field surveys of bed surface grain-size over a 5-km reach including 14 check dams. The analysis of the historical rainfall records showed a slight decrease in the amount and erosivity of precipitation. Mapping of land-use changes highlighted a general increase of vegetal coverage on the slopes adjacent to the monitored reaches. Together with the check dam network installation, this increase could have induced a reduction in water and sediment supply. The different erosional and depositional forms and adjustments showed a general narrowing between consecutive check dams together with local modifications detected upstream (bed aggradation and cross-section expansion together with low-flow realignments) and downstream (local incision) of the installed check dams. Changes in the torrent bends were also detected as a response to erosional and depositional processes with different intensities. The study highlighted: the efficiency of check dams against the disrupting power of intense floods by stabilizing the active channel and the influence of reforestation in increasing hillslope protection from erosion and disconnectivity of water and sediment flows towards the active channel. Only slight management interventions (for instance, the conversion of the existing check dams into open structures) are suggested, in order to mobilize the residual sediment avoiding further generalized incision of the active channel and coast line erosion. Copyright

Evaluating the crop and management factor C for applying RUSLE at plot scale

The successful application of empirical models like RUSLE for estimating soil erosion in rangeland areas depends heavily on the availability of reliable procedures for evaluating the crop and management factor C. In many cases such procedures make important assumptions regarding the plant growth component in response to land use for both annual and perennial plants. Such assumptions are frequently untested and the associated models thus remain largely invalidated. This contribution describes the results of an experiment involving 9 experimental plots located in Southern Italy aimed at validating several of the assumptions commonly associated with the use of RUSLE for estimating soil erosion at plot scale. At first, the soil loss measurements carried out in 2001 and 2002 are used to evaluate the crop and management factor for perennial plants. Then, an independent procedure involving biomass measurements for evaluating the C factor is proposed. Finally, a Monte Carlo technique is used for evaluating the effects of the knowledge uncertainty and the stochastic variability of the model parameters on calculated soil loss.

Evaluating the effects of check dams on channel geometry, bed sediment size and riparian vegetation in Mediterranean mountain torrents

In mountain streams possible negative impacts of check dams on soil, water and riparian vegetation due to check dam installation can be noticed. In spite of the ample literature on the qualitative effects of engineering works on channel hydrology, morphology, sedimentary effects and riparian vegetation characteristics, quantitative evaluations of the changes induced by check dams on headwater characteristics are rare. In order to fill this gap, this study has evaluated the effects of check dams located in headwaters of Calabria (Southern Italy) on hydrological and geomorphological processes and on the response of riparian vegetation to these actions. The analysis has compared physical and vegetation indicators in transects identified around check dams (upstream and downstream) and far from their direct influence (control transects). Check dams were found to influence significantly unit discharge, surface and subsurface sediments (both upstream and downstream), channel shape and transverse distribution of riparian vegetation (upstream) as well as cover and structure of riparian complexes (downstream). The actions of the structures on torrent longitudinal slope and biodiversity of vegetation were less significant. The differences on bed profile slope were significant only between upstream and downstream transects. The results of the Agglomerative Hierarchical Cluster analysis confirmed the substantial similarity between upstream and control transects, thus highlighting that the construction of check dams, needed to mitigate the hydro-geological risks, has not strongly influenced the torrent functioning and ecology before check dam construction. Moreover, simple and quantitative linkages between torrent hydraulics, geomorphology and vegetation characteristics exist in the analysed headwaters; these relationships among physical adjustments of channels and most of the resulting characteristics of the riparian vegetation are specific for the transect locations with respect of check dams. Conversely, the biodiversity of the riparian vegetation basically eludes any quantitative relations with the physical and other vegetal characteristics of the torrent transects.

Prediction of Surface Runoff and Soil Erosion at Watershed Scale: Analysis of the AnnAGNPS Model in Different Environmental Conditions

Negative effects of surface runoff and soil erosion in watersheds can be controlled and miti‐ gated through hydrological models. Moreover, they are suitable to simulate various combi‐ nations of different scenarios of land and water management in a watershed and therefore they are useful for comparative analysis of different options and as a guide to what Best Management Practices (BMPs) can be adopted to minimize pollution from point and non‐ point sources (Shrestha et al., 2006).

Hydrological Effects of Different Soil Management Practices in Mediterranean Areas

In Mediterranean environment intensive agricultural activities are often practiced in steep slopes, where sometimes climatic, geomorphologic and land use factors (e.g. the high rainfall intensity, the scarce vegetal coverage, especially on the occasion of the early rainfalls, the low organic matter content of soils, etc.) worsen the impacts of soil erosion. In such contexts agriculture may play an important role both in terms of economic and social spin-offs (e.g. peopling of hilly marginal lands) as well as under the environmental aspect (e.g. control of erosion phenomena). This is the case of olive growing practiced in hilly lands with a low tree density (e.g. in Southern Italy), often subjected to torrential rainstorms. Therefore, soil degradation problems in such agricultural steep lands under semi-arid conditions must be accounted for through proper soil management systems with low environmental impacts (mainly on soil hydrology). Until recently, the most common practice for soil conservation in many Mediterranean regions, as Andalusia (Spain, Gomez et al., 2003) and Sicily or Calabria (Italy) has been tillage: however, the tradition of frequent tillage, aimed at preventing competition from natural vegetation for water and nutrients with the olive tree and at facilitating olive harvesting, has exacerbated the problems of erosion and soil degradation (Gomez et al., 2009a). Alternative practices to tillage include: no-tillage with herbicides to maintain a bare and weed-free soil (which sometimes results in accelerated soil erosion due to an increase in water runoff) or the use of a cover crop to protect the soil during autumn and winter, either sown in early autumn or from the regeneration of the natural vegetation after the onset of rains (Gomez et al., 2009a, 2009c). The cover crop is controlled by mowing or by herbicide in spring to reduce the risk of competition for water with the trees, which represents the main limiting factor for plant growth in semi-arid lands, where the evapo-transpiration rate is very high and water resource is scarce. Studies on soil erosion in orchards in Mediterranean environment have analyzed the hydrological effects of the traditional different managements systems (e.g. Dastgheib & Frampton, 2000; Gago et al., 2007; Gomez et al., 2003, 2009b, 2009c; Monteiro & Moreira, 2004); the important role for soil conservation played by the crop cover has been also

Land spreading of solar-dried citrus peel to control runoff and soil erosion.

Marginal areas of southern Italy are often characterised by steep slopes and scarce vegetal coverage, which induce relevant runoff and soil erosion phenomena. On the other hand, the agricultural system of some Italian regions is characterized by the presence of many citrus industries, producing high amounts of by-products and wastewater. The possibility of spreading orange peel over land could represent an alternative solution for a more sustainable biomass disposal and, at the same time, protect against the risks soil erosion in Mediterranean areas. This paper reports the results of an experimental research activity aimed at evaluating the hydrological effects of land spreading of solar-dried citrus peel over steep plots (remodelled at 100%-slope), containing bare soil or covered by vegetation and exposed to natural rainfalls. The comparison of hydrological observations to those performed on untreated soils (“control”) highlighted that the addition of citrus peel to soil induced an appreciable reduction of runoff and particularly of sediment yield, due to the improvement of the soil properties, which encourages the establishment and development of vegetation.

Crop and management factor estimate for applying RUSLE in rangeland areas

The Revised Universal Soil Loss Equation (RUSLE) is a relatively simple model for estimating soil losses in agricultural lands and its use is attracting increasing attention around the world. Although all the factors in this model are receiving close attention and research is continuing to refine and improve the knowledge of how each factor affects erosion, much of research focus on the crop and management factor (C). Studies on the C-factor are continuing, not just for cropland where much of the research is occurring, but also for other agricultural land uses such as pasture, rangeland and forestland. In this paper, the results of a research involving 9 experimental plots located in Southern Italy aimed at validating some of the assumptions associated with the estimate of C-factor for rangeland conditions, are reported. The experiment involved rainfall, runoff and soil loss measurements for a three-year period which were used to evaluate the crop and management factor for perennial plants. Then, a simple procedure involving biomass seasonal measurements for evaluating the C-factor is proposed. The RUSLE model coupled with this empirical procedure showed good agreement between measured and calculated soil losses. Finally, in order to represent the model limitations and uncertainties, the effect of parameter uncertainty was studied by Monte Carlo method.