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Improving the management of irrigation schemes is a priority in the Mediterranean countries of the EU to achieve the objectives of the Water Framework Directive 2000/60EC. In the case of schemes based on open-channel networks for water conveyance and delivery, a limitation to the management efficiency is the huge number of gates that need to be controlled and regulated manually to adapt the flow to the actual irrigation water demand. Automated and coordinated gate regulation of large irrigation schemes has been successfully implemented in some areas of the world (e.g., NSW, Australia), but it implies huge public investments that are often unavailable. Opposite to this top–down approach, the Lombardy region (the largest irrigated region in the EU) has explored an approach based on funding small projects, which should demonstrate the potential of innovation in irrigation practice and foster the expansion of the most effective measures. In this paper, we analyze the effects of one of these projects, consisting in the substitution of a manual gate, controlling the supply of irrigation to a 150 ha irrigation district, with an automated, remotely controlled gate. Nine years of daily flow measurements at the district inlet, provided by the irrigation consortium that manages the gate, were compared with the rigid flow regulation that was applied when the inlet gate was manually regulated and with the irrigation water requirements simulated with a distributed agro-hydrological model widely used in the region for irrigation accounting and planning. The results show that the flexible regulation allowed by the new gate provided an average water saving of 12,000 m3/ha/year compared to the rigid regulation system. A further, though smaller, margin of improvement of 5000 m3/ha/year can be achieved with an optimal regulation that follows exactly the crop water requirements. A further interesting empirical evidence is that the simulation model fits very well the irrigation water requirements of the district using only easily accessible meteorological input data, without exploiting any information from ground or remote sensors to update soil moisture or crop developments during the season. This indicates that it could be effectively used, with very limited costs and effort, to support and improve the gate management. Finally, a preliminary economic analysis shows that the cost of the gate installation is sustainable, but the upscaling of this type of intervention to larger areas requires the support of public funding to cover approximately half of the cost of investment needed for the networking infrastructures.

Topographic depressions in Digital Elevation Models (DEMs) have been traditionally seen as a feature to be removed as no outward flow direction is available to route and accumulate flows. Therefore, to simplify hydrologic analysis for practical purposes, the common approach treated all depressions in DEMs as artefacts and completely removed them in DEMs’ data preprocessing prior to modelling. However, the effects of depression filling on both the geomorphic structure of the river network and surface runoff is still not clear. The use of two-dimensional (2D) hydrodynamic modeling to track inundation patterns has the potential to provide novel point of views on this issue. Specifically, there is no need to remove topographic depression from DEM, as performed in the use of traditional methods for the automatic extraction of river networks, so that their effects can be directly taken into account in simulated drainage patterns and in the associated hydrologic response. The novelty introduced in this work is the evaluation of the effects of DEM depression filling on both the structure of the net-points characterizing the simulated networks and the hydrologic response of the watersheds to simplified rainfall scenarios. The results highlight how important these effects might be in practical applications, providing new insights in the field of watershed-scale modeling.

Study region: The study region is represented by seven irrigation districts distributed under different climate and topography conditions in Italy. Study focus: This study explores the reliability and consistency of the global ERA5 single levels and ERA5-Land reanalysis datasets in predicting the main agrometeorological estimates commonly used for crop water requirements calculation. In particular, the reanalysis data was compared, variable-by-variable (e.g., solar radiation, R; air temperature, T; relative humidity, RH; wind speed, u; reference evapotranspiration, ET), with in situ agrometeorological observations obtained from 66 automatic weather stations (2008–2020). In addition, the presence of a climate-dependency on their accuracy was assessed at the different irrigation districts. New hydrological insights for the region: A general good agreement was obtained between observed and reanalysis agrometeorological variables at both daily and seasonal scales. The best performance was obtained for T, followed by RH, R, and u for both reanalysis datasets, especially under temperate climate conditions. These performances were translated into slightly higher accuracy of ET estimates by ERA5-Land product, confirming the potential of using reanalysis datasets as an alternative data source for retrieving the ET and overcoming the unavailability of observed agrometeorological data.

In this article, an open channel flow resistance equation, deduced applying dimensional analysis and incomplete self-similarity condition for the flow velocity distribution, was tested using measurements carried out in a full-scale channel equipped with three types of riparian plants (Salix alba L., Salix caprea L. and Alnus glutinosa L.). In the experimental channel, having banks lined with boulders, the vegetation branches were anchored in a concrete bottom. For each species, the measurements were carried out with plants having different amounts of leaves, different plant density and plant area index. The relationship between the scale factor Γ of the velocity profile and the Froude number was separately calibrated by measurements carried out without and with vegetation. The component of Darcy-Weisbach friction factor corresponding to the riparian vegetation fv was calculated as the difference between the measured friction factor value (channel grain roughness + vegetation) and that calculated for the channel without vegetation in the same hydraulic conditions. Using these fv values, the relationship between the scale factor Γ and the Froude number was calibrated. In this last relationship, a scaling coefficient a varying with the investigated vegetation type was introduced. This coefficient, as expected, gives the highest friction factor values for vegetation having branches with leaves. The theoretical flow resistance law, coupled with the relationship for estimating the Γ function having a scaling coefficient different for each investigated vegetation type, allowed an accurate estimate of the Darcy-Weisbach friction factor (errors less than or equal to 20% for 82.6% of the investigated cases). Finally, for the investigated vegetation species that are characterized by a condition with few leaves or leafless, the scaling coefficient a resulted strongly related to the bending stiffness. This analysis demonstrated that the highest Darcy-Weisbach friction factors correspond to vegetation species characterized by the highest values of bending stiffness. The friction factor values calculated for this last condition are characterized by errors that were less than or equal to ±20% for 90.6% of cases.

Urbanization modifies the hydrologic cycle, resulting in increased runoff rates, volumes, and peak flows in the drainage network. In this paper, the implementation of green roofs as source control solutions for mitigating the impacts of urbanization is analysed at the urban catchment scale. The hydrologic-hydraulic response of a 2 km2 urban basin is investigated under various implementation scenarios and rainfall characteristics. In particular, a distributed hydrologic model is employed to assess the impact of 4 spatially homogeneous installations of green roofs (25%, 50%, 75%, 100% of roofs area converted) when forced by 6 storms differing in both duration and return period. In addition, a spatially heterogeneous configuration is tested, with green roofs concentrated where the drainage network is more prone to high degrees of filling. Results show that implementing green roofs at the urban watershed scale can be considered a valuable strategy to reduce both flow peak and volume in urban drainage networks, although the approach is more effective for frequent storms of smaller magnitude. In addition, it is found that the urban system may respond non-linearly to the extent of green roofs implementation in terms of peak flow reduction at the network outlet, and that non-linearity is mainly related to the network being close to its flow convey capability. Finally, planning redevelopment efforts on the basis of local insufficiencies in network convey capacity has the potential of increasing the effectiveness of Low Impact Development solutions.

Italy is the leading rice producer in Europe, accounting for more than half of the total high-quality production of this crop. Rice is traditionally grown in fields that remain flooded starting with crop establishment until close to harvest. The water management in rice areas requires a high level of labor because it is based on maintaining a predetermined water height in paddy fields and because the regulation of input and output flow is typically operated manually by the farmers. This study aims to evaluate the hydraulic, control and economical performances of the first automatic and remote-controlled system applied for traditional rice irrigation in Europe and tested in Italy during 2016 agricultural season. In particular, (i) the effects of automation on the water balance; (ii) the reliability of the irrigation system for a real-time control of flow regulation and water level management in the field and (iii) the economic viability of the investment are investigated. The results show that, despite the automatic system has not proven a decrease of water consumptions (ranging from 2000 to 3700 mm) or a significant increase of rice yield (of about 8 ton hectare−1), it has not revealed any mechanical malfunctioning during the irrigation season and it allows to drastically reduce the time spent by workers for water level control and flow regulation. Lastly, the price of the automatic irrigation system (ranging from 638 to 689 € hectare−1) appears to be in good agreement with respect to the willingness of farmers for innovation.

Water retention characteristics are fundamental input parameters in any modeling study on water flow and solute transport. These properties are difficult to measure and for that reason, we usually need to use direct and indirect methods to determine them. An extensive comparison between measured and estimated results is needed to determine their applicability for a range of different soils. However this study attempts to make a contribution specifically in this connection. These properties were determined in two representative sites located in Landriano field, in Lombardy region, northern Italy. In the laboratory we used the pressure plate apparatus and the tensiometric box. Field soil water retention was determined including measurements of soil water content with SENTEK probes and matric potential with tensiometers. The soil waer retention curves (SWRC) were also settled on with some recently developed pedo-transfert functions (PTFs). Field retention curves were compared against those obtained from PTFs estimations and laboratory measurements. The comparison showed that laboratory measurements were the most accurate. They had the highest ranking for the validation indices (RMSE ranging between 2.4% and 7.7% and bias between 0.1% and 6.4%). The second best technique was the PTF Rosetta (Schaap et al. 2001). They perform only slightly poorer than the laboratory measurements (RMSE ranging between 2.7% and 10% and bias between 0.3% and 7.7%). The lowest prediction accuracy is observed for the Rawls and Brakensiek (1985) PTF (RMSE ranging between 6.3% and 17% and bias between 5% and 10%) which is in contradiction with previous finding (Calzolari et al., 2001), showing that this function is well representing the retention characteristics of the area. Due to time and cost investments of laboratory and field measurements, we conclude that the Rosetta PTF developed by Schaap et al. (2001) appears to be the best to predict the soil moisture retention curve from easily available soil properties in the Lombardy area and further field investigations would be useful to support this finding.

Exponentially growing water demands and increasingly uncertain hydrologic regimes due to changes in climate and land use are challenging the sustainability of agricultural water systems. Farmers must adapt their management strategies in order to secure food production and avoid crop failures. Investigating the potential for adaptation policies in agricultural systems requires accounting for their natural and human components, along with their reciprocal interactions. Yet this feedback is generally overlooked in the water resources systems literature. In this work, we contribute a novel modeling approach to study the coevolution of irrigated agriculture under changing climate, advancing the representation of the human component within agricultural systems by using normative meta-models to describe the behaviors of groups of farmers or institutional decisions. These behavioral models, validated against observational data, are then integrated into a coupled human-natural system simulation model to better represent both systems and their coevolution under future changing climate conditions, assuming the adoption of different policy adaptation options, such as cultivating less water demanding crops. The application to the pilot study of the Adda River basin in northern Italy shows that the dynamic coadaptation of water supply and demand allows farmers to avoid estimated potential losses of more than 10 M€/yr under projected climate changes, while unilateral adaptation of either the water supply or the demand are both demonstrated to be less effective. Results also show that the impact of the different policy options varies as function of drought intensity, with water demand adaptation outperforming water supply adaptation when drought conditions become more severe.

Rice cultivation requires a significant share of irrigation water, mostly because of the practice of continuous flooding; therefore, interest for alternative water managements is increasing. The paper presents results of a 2-year experiment in Northern Italy comparing three rice water managements: Water seeding-continuous FLooding (WFL), Dry seeding-delayed FLooding (DFL) and Dry seeding-intermittent IRrigation (DIR). The main objective was to assess the effects of water regimes on the agroecosystem as a whole (from water use and yield components to nutrient dynamics, etc.). This paper is focussed on water use aspects with the aim of: (1) comparing and discussing water balance terms, water use efficiencies and water productivities; (2) analysing percolation fluxes of flooded treatments (WFL and DFL); and (3) discussing interannual variations of paddy irrigation requirements due to environmental factors. Net irrigation requirements of WFL ranged between 1500 and 3000 mm in the two seasons, while DFL and DIR determined average reductions by 20 and 60 %. On the other hand, WFL provided an average yield of 10.2 t ha−1, which decreased by 3 and 28 % in DFL and DIR, respectively. Between-years variability can be attributed to environmental factors including groundwater levels and soil responses to abiotic and biotic factors. Percolations of flooded treatments showed a strong correlation with groundwater levels, especially during the first part of the season (R 2 0.90 and 0.95, respectively). Data analysis highlighted complex subsurface water dynamics dependent on groundwater levels and influenced by soil characteristics.

Studies conducted at the field scale report significant reductions in the irrigation requirements of rice when continuous submergence (CS) is replaced by less water-demanding regimes such as flush-irrigation (FI, i.e. intermittent irrigations of rice growing in non-submerged soils). However, the effects of their extensive application in paddy areas with shallow groundwater is much less studied. We present a scenario analysis investigating the impacts on irrigation requirements induced by a shift from CS to FI in an irrigation district of Northern Italy where rice is the main crop, followed by maize and poplar. The area is characterised by a shallow water Table whose depth fluctuates between two meters (in winter) and less than 1m (in summer). We applied a three-stage procedure, where we first analysed present state conditions using the SWAP (Soil, Water, Atmosphere, Plant) model to simulate irrigation deliveries and percolation fluxes. Then, we calibrated an empirical relationship between estimated percolation fluxes and measured depths to groundwater. Finally, we applied this relationship, in combination with the SWAP model, to predict the variation of district irrigation requirements due to a widespread shift from CS to FI. Results show that neglecting the feedback between groundwater recharge due to irrigation and groundwater depth led to overestimating the reduction of irrigation requirements of rice, which decreased from around 80% when no feedback was considered to around 60% when it was accounted for. Moreover, increased groundwater depths resulted in higher irrigation requirements for maize with an estimated growth of more than 50% due to the need of shortening the irrigation turn. These results demonstrate the importance of considering the impacts on the hydrological processes at larger scales when planning the conversion of CS into more efficient field irrigation methods.

Recent research suggests that groundwater overdraft can be mitigated by application of water onto agricultural lands for direct groundwater recharge. This technique is often called Agricultural Managed Aquifer Recharge (Ag-MAR) and is carried out in wintertime. Winter flooding of rice paddies could be considered as a form of Ag-MAR. Currently, it is implemented in Europe as an environmentally friendly practice, which could also bring many agronomic and hydrological benefits; however, especially the latter aspects have been poorly investigated in the past. Results of a hydrological study focused on winter flooding in three rice areas in northern Italy and lasting 18 months (winter seasons 2017–2018 and 2018–2019, and summer season 2018) are presented in this paper. The objective of winter flooding was to maintain higher groundwater levels till the beginning of the agricultural season in order to increase rice irrigation efficiency and protect some groundwater dependent ecosystems. Main findings are: (1) the percolation efficiency of winter flooding is very high (92–97% of the water volume applied on the fields); (2) local groundwater levels underneath the recharge areas increase at a similar rate as during the summer flooding and reach peak values that are close; (3) however, the rate of level decrease after the end of the flooding period is much faster with the winter flooding, when pre-flooding groundwater levels are re-established in 1 month, in contrast with at least 2 months with the summer flooding: this is due to the fact that the areas adopting winter flooding are less extended and more fragmented than the ones flooded during the agricultural season; (4) consequently, to maintain higher groundwater levels until the beginning of the cropping season, winter flooding should last longer and involve larger areas.

About 90 % of the global rice production takes place in Asia, while European production is quantitatively modest. Italy is the Europe’s leading producer, with over half of total production concentrated in a large, traditional paddy rice area in the north of the country. High irrigation requirement for continuous flooding encourages the adoption of water saving techniques. In 2013, an intense monitoring activity was conducted on two fields characterized by continuous flooding and intermittent irrigation regimes, with the aim of comparing their agronomical and hydrological effects, including their influence on the energy balance. An eddy covariance station was installed on the levee between the two fields, to monitor latent (LE) and sensible (H) heat fluxes as a function of wind direction. Additionally, the fields were instrumented with net radiometers, soil heat flux (G) plates, thermistors, tensiometers, and multilevel moisture probes. Three footprint models were applied to determine position and size of the footprint area at each monitoring time step, providing similar results. Two half-hourly turbulent fluxes datasets were obtained, one for each irrigation regime, each one comprising about 10 % of the daytime time steps over the agricultural season. The reliability of the monitoring performed with a single EC station was confirmed by the energy balance closure (H + LE versus Rn-G), showing an imbalance lower than 10 % for both the regimes. A detailed analysis of the effect of the storage terms on the ground heat flux estimation and a more thorough analysis of the radiation balance for the two plots were also performed.

The approaches for the estimation of evapotranspiration (ET) can be classified in “direct” methods, based on the original Penman–Monteith (PM) equation, in which the canopy resistance rc is modelled, and “indirect” methods, based on the preliminary calculation of ET for a well-watered reference grass (ETo) with a constant rc, which is then multiplied by a crop coefficient Kc to obtain ET. Even if the latter approaches are more widely adopted for their practical simplicity, many authors show that the former often provide better ET estimates in absence of calibration of crop parameters. In this study the performances of different direct and indirect methods were evaluated in the case of a surface irrigated maize grown in the Padana Plain (Northern Italy). The “one-layer” original PM equation with three different models for rc (Monteith, Jarvis, Katerji–Perrier), the “two-layers” PM model proposed by Shuttleworth and Wallace, the “single” and “double crop coefficient” models illustrated in the Paper FAO-56 were compared to latent heat fluxes measured in 2006 by eddy-covariance techniques. Results confirm that direct methods are more performing. The FAO-56 models with generalized crop coefficients overestimate ET, especially during the middle growth stage.

Soil moisture dynamics are affected by complex interactions among several factors. Understanding the relative importance of these factors is still an important challenge in the study of water fluxes and solute transport in unsaturated media. In this study, the spatio-temporal variability of surface soil moisture was investigated in a 10. ha flat cropped field located in northern Italy. Soil moisture was measured on a regular 50. ×. 50. m grid on seven dates during the growing season. For each measurement campaign, the spatial variability of the soil moisture was compared with the spatial variability of the soil texture and crop properties. In particular, to better understand the role of the vegetation, the spatio-temporal variability of two different parameters - leaf area index and crop height - was monitored on eight dates at different crop development stages. Statistical and geostatistical analysis was then applied to explore the interactions between these variables. In agreement with other studies, the results show that the soil moisture variability changes according to the average value within the field, with the standard deviation reaching a maximum value under intermediate mean soil moisture conditions and the coefficient of variation decreasing exponentially with increasing mean soil moisture. The controls of soil moisture variability change according to the average soil moisture within the field. Under wet conditions, the spatial distribution of the soil moisture reflects the variability of the soil texture. Under dry conditions, the spatial distribution of the soil moisture is affected mostly by the spatial variability of the vegetation. The interaction between these two factors is more important under intermediate soil moisture conditions. These results confirm the importance of considering the average soil moisture conditions within a field when investigating the controls affecting the spatial variability of soil moisture. This study highlights the importance of considering the spatio-temporal variability of the vegetation in investigating soil moisture dynamics, especially under intermediate and dry soil moisture conditions. The results of this study have important implications in different hydrological applications, such as for sampling design, ranking stability application, indirect measurements of soil properties and model parameterisation. © 2013 Elsevier B.V.

Pesticide losses to water can present problems for environmental management, particularly in catchments where surface waters are abstracted for drinking water supply. The relative role of different transfer pathways (spray drift, spills, overland flow and leaching from soils) is often uncertain, and there is a need for experimental observation and modelling to ensure that processes are understood under a range of conditions. Here we examine the transport of propyzamide and carbetamide in a small (15.5 ha) headwater sub-catchment dominated by an artificially drained field with strongly undulating topography (topographic gradients >1:10). Specifically, we explore the validity of the "field-scale lysimeter" analogy by applying the one dimensional mathematical model MACRO. Although one dimensional representation has been shown to be reasonable elsewhere, the scale and topography of the monitored system challenge many of the underlying assumptions. MACRO considers two interacting flow domains: micropores and macropores. The effect of subsurface drains can also be included. A component of the outflow from the main drain was identified as originating from an upslope permeable shallow aquifer which was represented using a simple groundwater model. Predicted herbicide losses were sensitive to drain spacing and the organic carbon to water partition coefficient, K(OC). The magnitude of the peak water and herbicide transport and their timing were simulated satisfactorily, although model performance was poor following a period of one month when snow covered the ground and precipitation was underestimated by the rain gauge. Total herbicide loads were simulated adequately by MACRO, suggesting that the field-scale lysimeter analogy is valid at this scale, although baseflow contributions to flow needed to be accounted for separately in order to adequately represent hydrological response.

Modern and effective water management in large alluvial plains that have intensive agricultural activity requires the integrated modeling of soil and groundwater. The models should be complex enough to properly simulate several, often non-linear, processes, but simple enough to be effectively calibrated with the available data. An operative, practical approach to calibration is proposed, based on three main aspects. First, the coupling of two models built on well-validated algorithms, to simulate (1) the irrigation system and the soil water balance in the unsaturated zone and (2) the groundwater flow. Second, the solution of the inverse problem of groundwater hydrology with the comparison model method to calibrate the model. Third, the use of appropriate criteria and cross-checks (comparison of the calibration results and of the model outputs with hydraulic and hydrogeological data) to choose the final parameter sets that warrant the physical coherence of the model. The approach has been tested by application to a large and intensively irrigated alluvial basin in northern Italy.

A review of the main instruments developed in Italy over more than two centuries to measure flow velocity of experience is presented, highlighting the relation with the development of hydraulics as a physical–mathematical science from the seventeenth century. The number and variety of Italian velocity meters partly reflect the vitality of a tradition, characterized by political polycentrism and rivalry among the individual cities and universities. In other aspects, the invention of ever-newer measuring instruments corresponds to the attitude of many of the early Italian hydraulicians, who interpreted hydraulics as a science of nature, based almost exclusively on observation and experience, which requires rather the gift of intuition than mathematical deduction. This work is part of a project of the BEIC Library and of the University of Milan, which will make available digital versions of hundreds of Italian historic texts of hydraulics on the portal www.beic.it.

Complex decision-making problems, related to planning and management of irrigation water resources, generally preclude the use of large, distributed-parameter models, which are then commonly substituted by lumped-parameter models. This paper, with the aim of improving the quality of these latter, introduces a new approach for their design. This approach is based on metamodelling, which proposes to identify a simple, lumped-parameter model on the basis of the data produced via simulation with a distributed-parameter model. The approach proposed is tested on a real-world case study, namely the identification of a metamodel describing the water demand of the Muzza-Bassa Lodigiana irrigation district (Italy). The metamodel, which inherits the physical description of the original distributed-parameter model, is sufficiently simple to permit the resolution of an optimal control problem, i.e. the design, via stochastic dynamic programming, of the release policy of Lake Como, serving the Muzza irrigation district.

The work presents the results of a comprehensive modelling study of surface and groundwater resources in the Muzza–Bassa Lodigiana irrigation district, in Northern Italy. It assesses the impact of changes in land use and irrigation water availability on the distribution of crop water consumption in space and time, as well as on the groundwater resources. A distributed, integrated surface water-groundwater simulation system was implemented and applied to the study area. The system is based on the coupling of a conceptual vadose zone model with the groundwater model MODFLOW. To assess the impact of land use and irrigation water availability on water deficit for crops as well as on groundwater system in the area, a number of management scenarios were identified and compared with a base scenario, reflecting the present conditions. Changes in land use may alter significantly both total crop water requirement and aquifer recharge. Water supply is sufficient to meet demand under present conditions and, from the crop water use viewpoint, a reduction of water availability has a positive effect on the overall irrigation system efficiency; however, evapotranspiration deficit increases, concentrated in July and August, when it may be critical for maize crops.

Neglecting hydrodynamic dispersion in models of river water quality has important implications in terms of simplifying the equations which describe the system and for model calibration. In this paper we analyze the behavior of a river system subjected to a time-variable point source input of a degradable solute using frequency response techniques applied to one-dimensional solute transport models, considering the combined effect of amplitude attenuation and phase shift due to hydrodynamic dispersion. We derive exact and simplified expressions that can be used for establishing whether dispersion is negligible at a desired level of accuracy. Finally, we present an application of the analysis to the river Lambro in northern Italy which receives diurnally varying solute loads from an undersized sewage treatment plant. The results obtained show the following: (1) In the case of a time-constant solute input, exact analytical expressions of the error incurred by neglecting dispersion can be derived which show that dispersive transport is negligible in most quasi steady state cases. (2) When solute input varies sinusoidally with time, the error due to neglecting dispersion is strongly dependent on the input frequency and may be significant if the input frequency is high. The error is practically independent of the decay rate coefficient, k, except when k is significantly greater than the input frequency. (3) Ignoring solute transport upstream from the outfall, due to dispersion, in the solution to the advection dispersion equation (ADE) can result in significant errors if the input frequency is sufficiently high. In some cases the choice of the ADE solution employed may have a larger impact than neglecting dispersion altogether.

The hydrological response of a catchment is the result of combined hillslope and channel network delays in the translation of rainfall to discharge at the catchment outlet. In this paper we examine three simple descriptions of the channel network response following an instantaneous hillslope runoff input within a general framework in which the role of network morphology is described using the probability density function (pdf) of network path lengths, and the role of hydrodynamic dispersion is described using a solution of the linear advection dispersion equation. We show that the pdf of path lengths, represented by the area function, can be adequately approximated by a triangular distribution with just two parameters (the mean and maximum network path lengths). The triangular pdf can be combined with a description of residence times in individual paths to derive an analytical expression for the hydrological response of the channel network. This expression provides a better approximation of the network response than both the original geomorphological instantaneous unit hydrograph (GIUH), based on Horton–Strahler ratios, and a single-channel representation, based on the concept of geomorphological dispersion. Using the same expression, we show that geomorphological factors generally prevail in controlling the mean and variance of network residence times. In contrast, hydrodynamic dispersion is shown to have a significant influence on the skewness of the network response over a wide range of catchment characteristics, strongly influencing the hydrograph peak and time to peak values in these cases. Copyright © 1999 John Wiley & Sons, Ltd.

A simple point-source water quality model was constructed to explore hypothetical scenarios of linear alkylbenzene sulphonate (LAS) load variability, chemical degradation kinetics, river discharge and river velocities within the context of planned water quality monitoring in the river Lambro, northern Italy. LAS is an anionic surfactant and a commonly used ingredient of household detergents. Input loads were derived from flow and concentration measurements at sewage treatment works (STW). River travel times are approximated using hydraulic geometry concepts based on existing records of stage, discharge and velocity measurements. The model proved to be especially useful in predicting the impact of overflows from an undersized STW near the top of the catchment on diurnal variations in water quality downstream. Probability density functions (pdf's) of LAS concentrations for a number of points on the river were approximated by running the model stochastically (using a Monte Carlo procedure) over independent frequency distributions of discharge, temperature and input load. The predicted concentration pdf's were then used to estimate the number of random grab and 24 h composite samples, which would be required in order to estimate mean concentrations with confidence. This is especially important in situations where the analysis is expensive and the sample budget is limited. The model results showed that grab sampling was not a viable strategy in the Lambro largely due to the very strong diurnal variability in concentrations induced by the STW overflow. This conclusion was corroborated by field data.

The influence of the method of identification of the drainage network on its geomorphological characteristics and on its hydrological response is analysed. Blue lines, photo-interpreted networks and networks generated from digital elevation models (DEMs) by an automatic algorithm are compared with field observations for two small alpine catchments. The comparisons are carried out in quantitative terms by using several geomorphological indices and functions and by calculating the hydrological response of the networks as represented by their geomorphologic instantaneous unit hydrograph (GIUH). The results show that the effect of the identification method on the geomorphological indices and on the hydrological response is significant, and that the threshold area for channel initiation is not constant. Moreover, the available data show a poor correlation between local slope and threshold area. Finally, the influence of the threshold area on the shape of the GIUH is larger when the residence time on the hillslopes is of the same order as the residence time in the network. In the opposite case, the variability of the flow velocity along the network seems to play an important role. © 1997 John Wiley & Sons, Ltd.

The optimal flow allocation in the Zambezi system, the largest multi-reservoir water resources system in southern Africa, is analysed. The problem is formulated in network terms and solved with a network flow algorithm. The present configuration of the system is taken as the reference to evaluate the benefits of the proposed modifications to the existing hydropower schemes. The introduction of additional operational constraints is also considered in order to analyse the costs of environmental protection of paludal ecosystems and to account for secondary objectives (e.g. irrigation, fishery, navigation). The results show that the upgrade of Kafue Gorge scheme through the addition of a new generator stage is the most advantageous from the hydropower production view point. In addition, the protection of paludal ecosystems through periodic controlled flooding and an increase of withdrawals for irrigation purposes may be achieved without dramatically changing the hydroelectric energy production.

Italy is one of the most important maize producers in the EU, and the Po Valley plain in northern Italy is the largest maize area in the country, with over 1 million ha planted. Water consumption for maize is very high because the crop covers almost 30% of the agricultural land of the plain and is irrigated mainly by border irrigation. Conversion to more efficient methods is currently under discussion for many areas. Whatever the irrigation method adopted, an accurate knowledge of maize irrigation requirements is essential to improving irrigation scheduling and water use planning on a regional scale. The FAO-56 “single crop coefficient” procedure is currently the most widely used procedure for the estimation of crop irrigation requirements. However, in the last 15 years, many authors have shown that FAO-56 crop coefficients, even if adjusted to account for local conditions (climate, soil, irrigation and crop management), may differ by up to ±40% from experimentally determined values. In this study, K c was derived as the ratio of the actual crop evapotranspiration in well-watered conditions (ET c ), as measured by the eddy covariance technique at two maize fields over three years, to the reference crop evapotranspiration ETo. The crop cycle length ranged from 136 to 146 days, depending on the year and the harvesting date, and the accumulated growing degrees-days (GDD) varied from 1590 to 1730 °C for silage and grain maize, respectively. The average locally developed K c values for initial, middle and late growing seasons were 0.33, 0.99 and 0.89–0.35 (the K c-end value depends on the harvesting time). The experimental K c-mid was 15% lower than the FAO-56 value adjusted for local conditions. Average seasonal ET c values were 430 and 400 mm for grain and silage second-crop maize, respectively

A simple model for estimating likely spatial patterns in landscape-scale denitrification rates is described. In the absence of limiting nitrate concentration, denitrification is assumed to be controlled principally by the soil water regime and the amount of available soil carbon. A formulation of TOPMODEL is used to estimate the spatial distribution of water table depths. Soil carbon concentration is assumed to decrease exponentially with depth. The spatial distribution of carbon concentrations at the soil surface is assumed to be imperfectly correlated with the topographic index used in TOPMODEL. Monte Carlo simulation techniques were used to introduce a stochastic element to the spatial distribution of soil carbon. This allowed estimates of the uncertainty in model outputs, resulting from uncertainties in the distribution and variability of soil carbon to be made. The model predicted spatial and temporal patterns of nitrate-non-limiting denitrification for a 15 year period in the Slapton Wood catchment in southwest England. Predicted denitrification followed a slight seasonal pattern with a winter maximum. Total annual denitrification losses tended to be positively correlated with total annual precipitation in the catchment. Highest rates tended to be predicted near to the stream. The modelling approach provides a means of assessing the proximity of local-scale field measurements to probable landscape-scale denitrification fluxes. Combining a deterministic model core with a stochastic generation of model parameters or state variables provides an attractive way of embracing variability and uncertainty whilst maintaining a conceptual description of the system dynamics. Copyright © 2002 John Wiley & Sons, Ltd.

Traditionally, most irrigation practices in Southern Europe have been based on gravity-fed surface irrigation systems. Currently, these systems remain a relevant typology in the European Union (EU) member states of the Mediterranean areas, where it is often the only sustainable method for farmers due to the small size of agricultural holdings, their reduced capacity and readiness to invest and the low ratio between yield profits and irrigation costs. In the last several years, in response to European and national directives, surface irrigation has garnered increasing attention at the political and bureaucratic levels due to frequent criticisms of its postulated low efficiency and high water wastage. However, these systems commonly provide a number of ecosystem services and nature-based solutions that increase the positive externalities in different rural socio-ecological contexts and often have the potential to extend these services and provide solutions that are compatible with economical sustainability. This study aims to discuss the prospects for new practices and for the rehabilitation and modernization of the gravity-fed surface irrigation systems in EU Mediterranean areas to enhance water efficiency, thus gaining both economic advantages and environmental benefits. The difficulties, stimuli for improvements and peculiarities of the irrigation water management of four rural environments located in Italy, Spain and Portugal were analyzed and compared to the current state of the gravity-fed surface irrigation systems with hypothetical future improvements achievable by innovative technologies and practices. In these different case studies, the current gravity-fed surface irrigation systems have an obsolete regulatory structure; water-use efficiency is not a driving criterion for the management of the conveyance and distribution canal network, and farmers are not yet adequately encouraged to adopt more efficient gravity-fed irrigation practices. A continuous knowledge exchange is thus necessary for the interaction of all irrigation water managers and farmers to improve their eco-efficiency and to preserve and promote their cultural heritage across the entire water supply and delivery chains. We argue that the best way forward will require precisely targeted rehabilitation measures of gravity-fed surface irrigation systems based on the integrated use of decision support services, gate automation, remote and feedback controls and real-time flow optimization.

In this paper an integrated modelling approach is presented and applied to a 26km stretch of the Lambro River downstream of the Merone Wastewater Treatment Plant in northern Italy. The sub-models used (ASM1 for the treatment plant and RWQM1 for the river) have been implemented in the WEST® simulator. Hydraulics and quality processes of the Lambro River have been modelled with a ‘tanks in series’ approach. The purpose of this study is to model the effect on river water quality of an insufficient treatment capacity of the WWTP. The plant was constantly operating at its maximum hydraulic capacity, leading to a daily bypass of dry weather wastewater, which imposed a marked diurnal cycle on pollutant concentrations in the river. The assessment of the actual WWTP upgrade has confirmed its beneficial effect on the river water quality.Keywords: ASM1, integrated modelling, LAS, model interfaces, RWQM1