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La corretta rappresentazione dei processi idrologici alla scala di versante è fon-damentale per la simulazione della risposta idrologica dei bacini idrografici durante eventi di pioggia intensa. I modelli basati sulla risoluzione dell’equazione di Richards possono simulare efficacemente le dinamiche della zona satura e non satura del suolo. Tuttavia essi richiedono una parametrizzazione onerosa, difficile da rilevare sperimentalmente sopratutto su ampie scale spaziali di applicazione. In questo lavoro di ricerca è stato sviluppato un modello idrologico monodimensionale di versante, in cui i processi di flusso laterale di falda sono rappresentati attraverso l’equazione di Darcy, mentre sono trascurati i processi dinamici nella zona non satura del suolo. L’effetto della ritenzione idrica capillare nella zona non satura è incorporato nel modello attraverso il termine della porosità drenabile del suolo che varia non linearmente in funzione della profondità della falda. A riguardo, l’assunto principale per la determinazione della porosità drenabile è che l’umidità nella zona non satura del suolo raggiunga istantaneamente la condizione di equilibrio idrostatico rispetto alla linea di falda. Il modello è stato applicato per la simulazione dell’andamento temporale del deflusso sottosuperficiale, dell’umidità del suolo e dei livelli di falda osservati in un ripido versante nel bacino idrografico del Lago di Baratz, in Sardegna. I parametri del modello, relativi alla trasmissività idraulica laterale e alle proprietà di ritenzione idrica del suolo, sono stati ricavati a partire dai dati idrologici raccolti. La calibrazione del modello è stata quindi limitata alle sole perdite idriche dovute a flussi laterali uscenti dal versante, di difficile quantificazione speri-mentale. Le performance predittive del modello sono risultate soddisfacenti, come con-fermato da coefficienti di efficienza di Nash-Sutcliffe prossimi a 0.8 per tutte le variabili idrologiche simulate. L'umidità del suolo, i livelli di falda e il deflusso sottosuperficiale sono stati ben riprodotti in termini di tempistica della risposta idrologica durante i periodi piovosi e di velocità di esaurimento nei periodi asciutti. Il modello sviluppato può essere effettivamente utilizzato per predire la risposta idrologica nei versanti naturali.

I versanti sono unità morfologiche fondamentali che governano la risposta idrologica dei bacini idrografici durante le precipitazioni più intense. Nonostante la loro riconosciuta importanza idrologica, è ancora necessario condurre approfonditi studi, sia a carattere sperimentale che teoretico, per meglio comprendere i meccanismi di generazione e trasporto del deflusso sottosuperficiale laterale saturo nei versanti. In questo contributo sono presentati i risultati di un monitoraggio di lungo periodo del flusso laterale di falda intercettato per mezzo di una trincea drenante installata su d’un ripido versante naturale nel bacino del Lago di Baratz, Sardegna. I dati raccolti vengono utilizzati per sviluppare una relazione di tipo esponenziale tra la conducibilità idraulica laterale satura (KS) e lo spessore della falda (T), valida alla scala di versante. I flussi osservati e i livelli di falda sono simulati con un modello numerico orizzontale 1D, basato sulla soluzione simultanea della legge del moto e dell’equazione di bilancio idrico, e implementato tramite uno schema risolutivo alle differenza finite. Le principali assunzioni del modello sono che nel suolo il flusso sottosuperficiale saturo sia regolato dalla legge di Darcy, e che si verifichi sempre l’istantaneo raggiungimento di un profilo di equilibrio idrostatico del carico di suzione nella zona vadosa. Il modello richiede la specifica della curva di ritenzione idrica del suolo e della relazione KS(T) ottenute sperimentalmente. I risultati della simulazione indicano che il modello è in grado di riprodurre in modo adeguato i dati osservati. Il flusso di falda è ben riprodotto, sia in termini di tempi di risposta che di portate drenate. Pertanto, il modello sviluppato può essere un utile strumento di previsione della risposta idrologica in versanti naturali a forte pendenza.

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.

Lateral saturated soil hydraulic conductivity, K-s,K-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 K-s,K-l and hydrological connectivity at the hillslope spatial scale. K-s,K-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 K-s,K-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 K-s,K-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 K-s,K-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 K-s,K-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 K-s,K-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 K-s,K-l at the same spatial scale.

International audience; The macroscopic capillary length, λc, is a fundamental soil parameter expressing the relative importance of the capillary over gravity forces during water movement in unsaturated soil. In this investigation, we propose a simple field method for estimating λc using only a single-ring infiltration experiment of the Beerkan type and measurements of initial and saturated soil water contents. We assumed that the intercept of the linear regression fitted to the steady-state portion of the experimental infiltration curve could be used as a reliable predictor of λc. This hypothesis was validated by assessing the proposed calculation approach using both analytical and field data. The analytical validation demonstrated that the proposed method was able to provide reliable λc estimates over a wide range of soil textural characteristics and initial soil water contents. The field testing was performed on a large database including 433 Beerkan infiltration experiments, with the 99% of the experiments yielding realistic λc values. The generated λc values were then used in conjunction with four different methods for estimating saturated soil hydraulic conductivity, Ks. Estimated Ks values were close to those generated by a reference method, with relative error < 25% in nearly all cases. By comparison, assuming constant or soil-dependent λc values caused relative errors in Ks of up to 600%. Altogether, the proposed method constitutes an easy solution for estimating λc, which can improve our ability to estimate Ks in the field.

Conversion of Mediterranean maquis and/or natural forest into agro-pastoral lands is a cause of soil degradation in many Mediterranean areas. Indicators of soil physical quality (SPQ) quantitatively linked to soil hydraulic properties are a valuable tool to assess the effect of land use changes. In this investigation, the Beerkan Estimation of Soil Transfer parameters (BEST) procedure for soil hydraulic characterization was used to estimate SPQ indicators. Four areas of the Baratz Lake watershed, Sardinia, Italy, characterized by both typical natural vegetation (holm oak [ Quercus ilex L.] forest and high maquis) and degraded vegetation (grassland established after fire or clearing of the maquis) were considered. The SPQ was assessed by either independently measured soil physical attributes, like soil bulk density, organic C content, saturated hydraulic conductivity, and sorptivity, and “capacitive” and “dynamic” indicators calculated from the water retention curve estimated by the BEST procedure. Measured and estimated SPQ indicators unanimously showed that clearing of the maquis caused a severe deterioration of SPQ associated with soil compaction, organic matter loss, and decrease of macropore volume and soil aeration capacity as well as reduced water circulation. A different and unexpected result was obtained for the fire-affected area, where the SPQ was comparable to that of the neighboring oak forest area. We deduced that vegetation restoration after fire passage contributed to maintain a high organic matter content and to mitigate rain compaction effects. We concluded that SPQ indicators derived by applying the BEST procedure are suitable to detect land degradation in the natural environments studied.

Soil surface sealing is a major cause of decreased infiltration rates and increased surface runoff and erosion during a rainstorm. The objective of this paper is to quantify the effect of surface sealing on infiltration for 3 layered soils with different textures for the upper layer and investigate the capability of BEST procedure to catch the formation of the seal and related consequences on water infiltration. Rainfall experiments were carried out to induce the formation of the seal. Meanwhile, Beerkan infiltration runs were carried out pouring water at different distances from the soil surface (BEST-H versus BEST-L runs, with a High and Low water pouring heights, respectively) for the same type of layered soils. Then, we determined saturated soil hydraulic conductivity, Ks, values from rainfall simulation and Beerkan infiltration experiments. Rainfall simulations carried out on soil layers having different depths allowed to demonstrate that infiltration processes were mainly driven by the seal and that Ks estimates were representative of the seal. Mean Ks values, estimated for the late-phase, ranged from 13.9 to 26.2 mm h−1. Soil sealing induced an increase in soil bulk density by 38.7 to 42.1%, depending on the type of soil. Rainfall-deduced Ks data were used as target values and compared with those estimated by the Beerkan runs. BEST-H runs proved more appropriate than BEST-L runs, those last triggering no seal formation. The predictive potential of the three BEST algorithms (BEST-slope, BEST-intercept and BEST-steady) to yield a proper Ks estimate for the seal was also investigated. BEST-slope yielded negative Ks values in 87% of the cases for BEST-H runs. Positive values were obtained in 100% of the cases with BEST-steady and BEST-intercept. However, poorer fits were obtained with the latter algorithm. The comparison of Ks estimates with rainfall-deduced estimates allowed to identify BEST-steady algorithm with BEST-H run as the best combination. The method proposed in this study could be used to easily measure the seal's saturated hydraulic conductivity of an initially undisturbed bare soil directly impacted by water with minimal experimental efforts, using small volumes of water and easily transportable equipment.

Soil infiltration processes manage runoff generation, which in turn affects soil erosion. There is limited information on infiltration rates. In this study, the impact of vine age on soil bulk density (BD) and hydraulic conductivity (Ks) was assessed on a loam soil tilled by chisel plough. Soil sampling was conducted in the inter row area of six vineyards, which differed by the age from planting: 0 (Age 0; just planted), 1, 3, 6, 13, and 25 years (Age 1, Age 3, Age 6, Age 13, and Age 25, respectively). The One Ponding Depth (OPD) approach was applied to ring infiltration data to estimate soil Ks with an α* parameter equal to 0.012 mm-1. Soil bulk density for Age 0 was about 1.5 times greater than for Age 25, i.e., the long-term managed vineyards. Saturated hydraulic conductivity at Age 0 was 86% less than at Age 25. The planting works were considered a major factor for soil compaction and the reduction of hydraulic conductivity. Compared to the long-term managed vineyards, soil compaction was a very short-term effect given that BD was restored in one year due to ploughing. Reestablishment of Ks to the long-term value required more time.

The lateral saturated hydraulic conductivity, Ks,l , is the soil property that mostly governs subsurface flow in hillslopes. Determinations of Ks,l at the hillslope scale are expected to yield valuable information for interpreting and modeling hydrological processes since soil heterogeneities are functionally averaged in this case. However, these data are rare since the experiments are quite difficult and costly. In this investigation, that was carried out in Sardinia (Italy), large-scale determinations of Ks,l were done in two adjacent hillslopes covered by a Mediterranean maquis and grass, respectively, with the following objectives: i) to evaluate the effect of land use change on Ks,l , and ii) to compare estimates of Ks,l obtained under natural and artificial rainfall conditions. Higher Ks,l values were obtained under the maquis than in the grassed soil since the soil macropore network was better connected in the maquis soil. The lateral conductivity increased sharply close to the soil surface. The sharp increase of Ks,l started at a larger depth for the maquis soil than the grassed one. The Ks,l values estimated during artificial rainfall experiments agreed with those obtained during the natural rainfall periods. For the grassed site, it was possible to detect a stabilization of Ks,l in the upper soil layer, suggesting that flow transport capacity of the soil pore system did not increase indefinitely. This study highlighted the importance of the experimental determination of Ks,l at the hillslope scale for subsurface modeling, and also as a benchmark for developing appropriate sampling methodologies based on near-point estimation of Ks,l .