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This paper firstly presents the temporal and spatial characteristics of short-term urban-scale rainfall. The studies are based on measurements of rainfall made on a network of 12 gauges situated in the city of Lund, Sweden. Three-year series of one-minute rainfall records from each gauge are used for the analyses such as areal intensity-duration-frequency relationships. Secondly, a method for real-time prediction in time and space of urban-scale rainfall under the assumption that the rainfall process is governed by the stochastic convective-dispersion equation. The method is applied to the shortterm rainstorm prediction in the city of Lund.

The two-parameter Weibull distribution (2PWD), similar to an instantaneous unit hydrograph (IUH), is parameterized in terms of Horton catchment ratios on the basis of a geomorphologic model of catchment response. For this the shape and scale parameters of the Weibull distribution are expressed analytically in terms of Horton's catchment ratios. The two parameters of the IUH derived using Nash's model, which is a two-parameter gamma distribution (2PGD), are also expressed analytically in terms of Horton ratios. The performance of the proposed methods is tested for describing a synthetic unit hydrograph (SUH) under limited data conditions. A comparison is made with the unit hydrographs derived from the event data of two real catchments, and with the existing geomorphological based 2PGD for developing SUH given by Rosso (1984). The sensitivity analysis of the 2PWD to the nondimensional parameter β of the UH (a product of peak discharge and time to peak) shows β to be more sensitive to the shape parameter a than the scale parameter b. Further examination to find any similarity between the behavior of 2PWD and 2PGD showed that a in 2PWD corresponds to the shape parameter n in the 2PGD, and b behaves similar to the scale parameter k in the 2PGD. Finally, practical applicability of the proposed approach to ungauged catchments is tested using field data. (Less)

The River Hoje in the south of Sweden is a typical receiving water for urban and rural runoff. Mass balance calculations over a 17-month period indicate that pollutants are retained in the sediments of the investigated 5-km-long reach of the stream (90 tons of biochemical oxygen demand (BOD7), 850 tons of chloride, 2.1 tons of copper, 3.2 tons of zinc, and 1.0 ton of lead). Other pollutants such as suspended solids and phosphorus appear to be both retained and washed-out, depending on loading rates and local stream conditions. The retained pollutants represent a substantial part of the total mass transport through the stream (14–47%). Almost half of the transported zinc is retained within the stream sediment. Subsequently, the deposited pollutants represent a potential pollution source. Analyses of sediment samples verify that the upper sediments contain high concentrations of heavy metals.

More than 40 years of re-vegetation using mainly xerophytic shrubs Artemisia ordosica Krasch. and Caragana korshinskii Kom. at Shapotou Desert Experimental Research Station near Lanzhou, China has resulted in established dwarf-shrub and herbaceous cover on sand dunes. Precipitation, as the sole source of water replenishment in the semiarid area, plays a pertinent role in sustaining the desert ecosystem. A field study was conducted to (a) measure interception loss on shrub canopies during individual rainfall events, (b) determine the canopy storage capacity of individual plants, and (c) explore the relationship between interception and rainfall parameters. The total rainfall and its respective partitions as throughfall were determined and the interception losses in the studied ecosystem were quantified. Interception loss was shown to differ among the xerophyte taxa studied. During the growing seasons, the average shrub community interception loss is 6.9% and 11.7% of the simultaneous overall preci...

The number of local and regional-scale water management failures appears steadily to increase despite an apparently higher level of engineering solutions at hand. The objective of this paper is to examine the challenges the existing education system needs to meet in order to produce water engineers capable of responding to the complexity of contemporary and future water problems in relation to societal needs. The next generation of water engineers may stay in their professional functions until 2040 or 2050. It is likely that in this period more critical water management and environmental problems will be experienced than have been encountered so far. The question then arises whether the present water engineers have the proper background education to understand environmental, hydrological, ecological and socio-economic problems to resolve related water management problems. Future water engineers must, to a greater extent, include socio-economic consequences in planned and/or designed water management systems and convey greater transparency regarding risks and societal effects.

Recently, substantial progress has been made in detection and observation of non-aqueous phase liquids (NAPLs) in the subsurface using different experimental techniques. However, there is still a lack of appropriate direct methods to measure the saturation of NAPL theta(NAPL)). This paper provides a guide for estimating theta(NAPL) and water content (theta(a)) in unsaturated and saturated sand based on direct measurements of soil dielectric constant (K-a) and electrical conductivity (sigma(a)) using time domain reflectometry (TDR). The results show that the previously used dielectric mixing model fails to predict, theta(NAPL) in the case of a four-phase system. A new methodology is suggested and exemplified by showing that the measured K-a gives accurate estimation of theta(NAPL) for a three-phase system while in a four-phase system, both sigma(a) and K-a need to be measured. The results show that using the suggested methodology, accurate predictions of theta(w) (R-2 = 0.9998) and theta(NAPL) lower than 0.20 m(3) m(-3) (average R-2 = 0.9756) are possible. (Less)

Land development often results in adverse environmental impact for surface and subsurface water systems. For areas close to the coast, land changes may also result in seawater intrusion into coastal aquifers. Due to this, it is important to evaluate potential adverse effects in advance of any land development. For evaluation purposes a combined groundwater recharge model is proposed with a quasi three-dimensional unconfined groundwater flow equation. The catchment water balance for a planned new campus area of Kyushu University in southern Japan, was selected as a case study to test the model approach. Since most of the study area is covered with forest, the proposed groundwater recharge model considers rainfall interception by forest canopy. The results show that simulated groundwater and surface runoff agree well with observations. It is also shown that actual evapotranspiration, including rainfall interception by forest canopy, is well represented in the proposed simulation model. Several hydrological components such as direct surface runoff rate, groundwater spring flow rate to a ground depression, trans-basin groundwater flow etc., were also investigated. (Less)

Water balances for a re-vegetated xerophyte shrub (Caragana korshinskii) area were compared to that of a bare surface area by using auto-weighing type lysimeters during the 1990-1995 growing seasons at the southeast Tengger Desert, Shapotou, China. The six-year experiment displayed how major daily water balance components might vary for a bare and a re-vegetated sand dune area. Evapotranspiration from the C korshinskii lysimeter represented a major part of the water balance. The average annual ET/P ratios varied between 69 and 142%. No seepage was observed for the vegetated lysimeter. For the bare lysimeter, on the other hand, 48 rum or 27% of observed rainfall per year occurred as seepage. These results suggest that re-vegetating large sandy areas with xerophytic shrubs could reduce soil water storage by transpiration. Also, the experimental results indicate that revegetating large sandy areas could significantly change groundwater recharge conditions. However, from a viewpoint of desert ecosystem reconstruction, it appears that natural rainfall can sustain xerophytic shrubs such as C. korshinskii which would reduce erosion loss of sand. However, re-vegetation has to be balanced with recharge/ groundwater needs of local populations. (Less)

Abstract In arid Tunisia, a tabia system is a traditional macrocatchment water harvesting system. It consists of a runoff area, which occupies two thirds of the slope and is traditionally used for grazing; and one to five cropped plots within U-shaped soil banks arranged in a cascade in the third downstream area. These ȁrun-onȁ areas accumulate and store the occasional runoff. Each soil bank is constructed with a discharge weir that allows modification of the flooded area and discharge of excess water towards downstream plots. Such a harvesting system, located in an area with 140 mm annual rainfall, was instrumented during four hydrological years (1995–1999) and 45 rainfall events were recorded. Eleven of these events gave a measurable inflow to at least one of the four plots. The observations showed that the traditional tabia system reduced total surface runoff from the catchment to essentially zero. The harvesting system significantly reduced peaks of surface runoff within the catchment, which ...

(2009). Reply to discussion of “Soil water content and salinity determination using different dielectric methods in saline gypsiferous soil”. Hydrological Sciences Journal: Vol. 54, No. 1, pp. 213-214.

The last century witnessed the development of numerousapproaches (e.g. linear, nonlinear, deterministic, stochastic,physics-based, data-based) for modeling and prediction ofour complex environmental systems. There is a plethora ofliterature debating whether any one of these approaches issuperior to any other (if at all such an evaluation can bemade), and why and how. While such debates continue, anexamination of environmental literature also reveals theexistence of some serious problems in our modelingpractice (see, for example, Beven 2002), regardless of theapproach adopted. For example: (1) we have a tendency,driven by our technological and methodological advances,to develop more complex models (having too manyparameters and requiring too much data) than that mayactually be necessary; and (2) the models are often devel-oped for specific situations, and their extensions to othersituations and generalizations are normally difficult. Whatis also being increasingly realized is that none of theexisting approaches is adequate for modeling and predic-tion of our environmental systems by itself. With ourincreasing emphasis on specific concepts/methods (see, forexample, Sivakumar 2005) for their ‘individual brilliance’(that normally reflect our extreme and biased views), ratherthan their ‘collective utility’ to address the real environ-mental challenges, the above situation may not changemuch in the future, unless a significant change in paradigmis adopted. The only way to overcome this situation seemsto be to find some ‘common grounds’ in our modelingapproaches, which is the primary motivation for this Spe-cial Issue entitled ‘‘Modeling and Prediction of ComplexEnvironmental Systems.’’ Towards pursuing this, the spe-cific objectives are:1. to disseminate the latest initiatives and developmentsin the modeling and prediction of our environmentalsystems, especially focusing on the applications ofdifferent concepts/methods; and2. to discuss (both philosophically and scientifically) thepotential for the formulation of a ‘middle-ground’approach for more realistic representations of ourenvironmental systems, and also to highlight theimportant challenges in this formulation.This Special Issue consists of 14 papers, contributed bya total of 40 authors. Each paper falls under either of theabove two objectives, and collectively they bring forth theapplications of various approaches/techniques to differentenvironmental systems/problems around the world. Thetechniques applied in these papers include (in the order oftheir appearance), among others: hidden Markov models(Jayawardena et al.; Kwon et al.), wavelet transforms(Jayawardena et al.; Kwon et al.), fractals and multifractals(Cortis et al.), nonlinear dynamics and chaos (Kim et al.;Singh et al.; Sivakumar), artificial neural networks (Aksoyand Dahamsheh; Bagtzoglou and Hossain), nonlinear sto-chastic models (Cayar and Kavvas), numerical methods(Perera et al.), self-organizing maps (Lischeid), statisticalestimation techniques (Bagtzoglou and Hossain; Deanet al.; Vrugt et al.), Bayesian approaches (Bagtzoglou andHossain; Vrugt et al.), and data-based mechanistic models(Young and Ratto). The environmental problems addressedin these papers are, among others: rainfall (Jayawardena

The present study concerns disaggregation of daily rainfall time series into higher resolution. For this purpose, the scaling-based cascade model proposed by Olsson (1998) is employed. This model operates by dividing each rainy time period into halves of equal length and distributing the rainfall volume between the halves. For this distribution three possible cases are defined, and the occurrence probability of each case is empirically estimated. Olsson (1998) showed that the model was applicable between the time scales 1 hour and 1 week for rainfall in southern Sweden. In the present study, a daily seasonal (April-June; 3 years) rainfall time series from the same region was disaggregated by the model to 45-min resolution. The disaggregated data was shown to very well reproduce many fundamental characteristics of the observed 45-min data, e.g., the division between rainy and dry periods, the event structure, and the scaling behavior. The results demonstrate the potential of scaling-based approaches in hydrological applications involving rainfall.

The assertion by the authors that n and depend on storm characteristics could be highly confusing. In essence, all parameters of the UH are dependent only on the physical characteristics of the studied catchment and should be constant for every storm. There is no reason in their development to infer any relationship with storm characteristics. The dependence on the observed hydrograph intervenes only when calibrating the UH parameters on observed rainfall-runoff data, as for any model. However, the most reliable estimates are obtained when pooling several storms together in the calibration process.

Climate change is likely to have severe effects on water availability in Ethiopia. The aim of the present study was to assess the impact of climate change on the Gilgel Abay River, Upper Blue Nile Basin. The Statistical Downscaling Tool (SDSM) was used to downscale the HadCM3 (Hadley centre Climate Model 3) Global Circulation Model (GCM) scenario data into finer scale resolution. The Soil and Water Assessment Tool (SWAT) was set up, calibrated, and validated. SDSM downscaled climate outputs were used as an input to the SWAT model. The climate projection analysis was done by dividing the period 2010-2100 into three time windows with each 30 years of data. The period 1990-2001 was taken as the baseline period against which comparison was made. Results showed that annual mean precipitation may decrease in the first 30-year period but increase in the following two 30-year periods. The decrease in mean monthly precipitation may be as much as about -30% during 2010-2040 but the increase may be more than +30% in 2070-2100. The impact of climate change may cause a decrease in mean monthly flow volume between -40% to -50% during 2010-2040 but may increase by more than the double during 2070-2100. Climate change appears to have negligible effect on low flow conditions of the river. Seasonal mean flow volume, however, may increase by more than the double and +30% to +40% for the Belg (small rainy season) and Kiremit (main rainy season) periods, respectively. Overall, it appears that climate change will result in an annual increase in flow volume for the Gilgel Abay River. The increase in flow is likely to have considerable importance for local small scale irrigation activities. Moreover, it will help harnessing a significant amount of water for ongoing dam projects in the Gilgel Abay River Basin.

Solute transport through the unsaturated zone is at present one of the most important research areas for evaluation and prediction of environmental hazards. We use tracer test data (Br-) from a semiarid experimental field in Tunisia to investigate effects of soil heterogeneity on the solute transport. Taylor’s frozen flow field hypothesis is used to derive Lagrangian correlation fields from Eulerian correlation fields using the two-dimensional solute data. The spatial dependence of solute concentration is anisotropic and strongly elongated in the horizontal due to soil layering. The correlation scale is about 0.5 m in the vertical but several times larger in the horizontal. These spatial patterns persist over 20–30 h. Soil water content displays a more random behavior as compared to Br- concentration. The loss of information on heterogeneity when increasing the horizontal measurement scale from 0.3 to 1.0 m appears significant.

Uncertainty and risk analyses are becoming more and more important in engineering sciences due to increasing climatic variation and other types of natural hazards. On average, every year infrastructure damages caused by earthquakes, floods, typhoons and other catastrophic events induce costs corresponding to hundreds of billions of dollars besides thousands of lives lost. Consequently, uncertainty and risk analyses are some of the most important subjects for engineers. In line with this, the author, Prof. Sergio E. Serrano, Temple University, has issued a second, completely revised text book on the subject. The book is a comprehensive collection of stochastic and statistical engineering techniques with uncertainty and risk analyses that are applicable in a broad range of problems. The focus is clearly on engineering applications rather than on theoretical derivation. Even rather advanced techniques involving nonlinear differential equations are solved analytically in supplied codes and presented with illustrative examples. The strong and very useful aspect of this text book is that it contains a multitude of solved examples as well as problems with answers. Consequently, the potential reader of this book might be engineering students as well as professional engineers. The book consists of fourteen chapters starting with a discussion of engineering uncertainty analysis and ending with a summary and discussion on seven steps for analysis of engineering problems. Chapter 2 introduces concepts of probability and frequency. Chapter 3 clarifies the concept of random variables with discrete and continuous variables. Chapter 4 then introduces the basics of random system modeling and Monte Carlo simulation. Chapter 5 presents the concept of several random variables and Chapter 6 introduces basic ideas of statistics. Chapter 7 shows how to fit probabilistic models to experimental data and then follows linear regression in Chapter 8. Chapter 9 explains how to develop models for reliability of engineering systems and Chapter 10 shows how to design engineering experiments. In Chapter 11 methods for testing experimental data are introduced together with ANOVA techniques. Chapter 12 is a synthesis of previous chapter in the way that it explains and visualizes random processes using explained Maple codes. Finally, Chapter 13 introduces novel techniques to solve linear and nonlinear differential equations by means of analytical methods. The above shows that it is a very comprehensive text book on uncertainty and risk. This together with solved examples and included Maple codes makes it one of the most useful books on the market for teaching engineering students as well solving practical engineering problems involving risk and uncertainty estimation. I am sure that the book will have a significant positive impact on improving engineering solving during coming decades.

[1] We aimed at investigating whether the spatial variability of infiltration in field soils, as visualized through dye infiltration experiments, is characterized by a multiscaling behavior. Digitized high-resolution dye images from three sites in an experimental catchment in Tunisia were analyzed using three indicators of scaling: empirical probability distribution functions, power spectra, and raw statistical moments. The two former indicators suggested a general scaling behavior of the data, which through the moments' analysis was found to be of multiscaling type. Random cascade processes are frequently used to model multiscaling processes, and we fitted the "universal multifractal'' (UM) model of Schertzer and Lovejoy [1987] to our data. The UM model closely reproduced the empirical K(q) functions, and simulated fields reproduced key features in the observed ones. The results indicate that multiscaling random cascade modeling is useful for statistically describing flow processes and solute transport under field conditions.

[1] Transport of nonaqueous phase liquids (NAPLs) in soils is becoming an increasingly serious threat to the environment. Detection and observation of these substances are thus an increasingly important issue. During recent years, studies have used the apparent dielectric constant (K-a) measured by time domain reflectometry (TDR) for determining the saturation of NAPLs (theta(NAPL)) in soils (m(3) m(-3)). K-a has been related to theta(NAPL) using dielectric mixing models. In this approach for the unsaturated zone, the water content theta(w) should be known beforehand (by assumptions or measured using other techniques). Here, unlike previous research, detailed laboratory experiments were conducted to investigate the relationship between the TDR measured K-a and bulk electrical conductivity sigma(a) and theta(NAPL). Calibration was made in homogeneous sand using three different NAPLs. It was shown that the mixing model used previously led to errors up to 0.05 m(3) m(-3) in saturated sand. Moreover, in unsaturated sand, measurements of Ka only cannot be used for estimation of theta(NAPL) even if theta(w) is known. Instead, TDR's capability of determining both K-a and sigma(a) was utilized to estimate theta(w) and theta(NAPL). The approach presented in this study can be used for simultaneous observation of theta(w) and theta(NAPL) during NAPL transport experiments in both unsaturated and saturated sandy soils. Thus it is potentially helpful when developing new NAPL transport models. (Less)

The reliability of the correlation dimension estimation in short hydrological time series is investigated using an inverse approach. According to this approach, first predictions are made using the phase-space reconstruction technique and the artificial neural networks. The correlation dimension is estimated next independently and is compared with the prediction results. A short hydrological series, monthly runoff series of 48 years (with a total of only 576 values) observed at the Coaracy Nunes/Araguari River watershed in northern Brazil, is studied. The correlation dimension results are in reasonably good agreement with the optimal embedding dimension obtained from the phase-space method and the optimal number of inputs from the neural networks. No underestimation of the correlation dimension is observed due to the small data size, rather there seems to be a slight overestimation due to the presence of noise in the data. The results indicate that the accuracy of the correlation dimension may not be judged on the basis of the length of the time series but on whether the time series is long enough to reasonably represent the dynamical changes in the system. Such an observation suggests that the correlation dimension could indeed be a reliable indicator of low-dimensional chaos even in short hydrological time series, which is certainly encouraging news for hydrologists who often have to deal with short time series. (Less)

Modeling of sunspots is important since they indicate the relative activity of the Sun which in turn influence different terrestrial properties. To predict the nonlinear and chaotic behavior of sunspot time series, the problem of reconstructing underlying system equations is studied. The proposed procedure for this is (1) based on the behavior of observed time series and dimension of strange attractor, find reference system equations (in our case the modified Rossler equations) that show similar basic features as the time series (e.g., appearance of attractor, amplitude and pseudoperiod), (2) assume a general structure of the governing system equations by Taylor series expansion, (3) use the reference equation systems as initial state in an updating procedure (extended Kalman filtering) to estimate the structure of the governing system equations. Using this procedure, results show that predictions on an average up to eight months ahead can be made with good agreement for sunspot time series after identifying the governing system equations. The extended Kalman filter was shown to be an efficient tool to identify parameter values and to make updated predictions of the chaotic system.

Two-year series of 1-min rainfall intensities observed by rain gages at six different points are analyzed to obtain information about the fractal behavior of the rainfall distribution in time. First, the rainfall time series are investigated using a monodimensional fractal approach (simple scaling) by calculating the box and correlation dimensions, respectively. The results indicate scaling but with different dimensions for different time aggregation periods. The time periods where changes in dimension occur can be related to average rainfall event durations and average dry period lengths. Also, the dimension is shown to be a decreasing function of the rainfall intensity level. This suggests a multidimensional fractal behavior (multiscaling), and to test this hypothesis, the probability distribution/multiple scaling method was applied to the time series. The results confirm that the investigated rainfall time series display a multidimensional fractal behavior, at least within a significant part of the studied timescales, which indicates that the rainfall process can be described by a multiplicative cascade process.

The spatial properties of the correlation structure based on daily rainfall data from 67 stations throughout Tunisia over a 5-year period are examined. The correlation structure is generally markedly anisotropic as influenced by topography and the coast. These two factors seem to influence the correlation pattern differently during different months. The mean areas within the 0.7 correlation isoline for all subgroups vary from about 1000 km2 in the early autumn to about 7000 km2 in the winter months.

When dealing with urban design, it is essential to have knowledge of the magnitude of the spatial variability of short high-intensive rainstorms. Most of the studies of high-intensive rainfall, conducted during recent years, concern regions with a humid climate. Still, the largest temporal and spatial variations in rainfall are to be found in arid and semi-arid regions. This paper sums up findings regarding rainfall variability, observed in a small catchment in northern Tunisia during a period of 2 yr. Point and areal intensities are presented for the ten most high-intensive storms observed. Storm-centered areal reduction factors are calculated for different durations and areas.

Temporal and spatial variability of soil water content on mainly two different scales is visualized by means of correlation analyses. The soil water data were collected at seven sites for a period of about ten years. The spatial variability of soil water in the unsaturated zone is illustrated and discussed from the aspects of interdepth, intersite and temporal changes respectively. The results in terms of the correlation structure show an increase in spatial variability when depth increases. Three soil layers with different patterns of variability are identified: 0–60, 60–140, and 140–240 cm. It is concluded that the mean time series values of the soil water content do not differ significantly within horizontal distances of about 10–20m. For distances of about 1100m this variation may be more than 5% by volume in absolute values. Higher spatial variability is noted during the summer period (May–September).

The function of combined sewer overflows (CSO) from both a quantitative and a qualitative point of view is often little known in the Nordic communities. Since large pollution loads are discharged from urban areas by CSO, it is important to consider this problem when rehabilitation plans are established. A study aiming at the estimation of yearly volumes of CSO and yearly quantities of pollution load from CSO has been carried out in the city of Malmö, Sweden. The CSO discharges into four different types of receiving waters: the channel, the harbour, the Sege River and the Öresund. Registration of frequency, duration and water volume was made at about 30 weirs at different time periods. Storm Water Management Model (SWMM) was used both to simulate single SCO events and for continuous simulation. The results from these simulations were compared with actual measurements. The total pollution load was estimated from mean concentration of pollutants from more than 100 samples taken at different weirs and CSO events. Through analysis of the occurrence of CSO in time and space, a program of priorities for the rehabilitation of the CSO-system was established.

Cross-correlation structures based on daily rainfall data recorded during a period of 5 years at 67 stations throughout Tunisia are used to examine spatial rainfall variability. Basic properties of the correlation-distance function such as cumulating period, exclusion versus inclusion of dry periods, and data volume are analysed. Analysis of the correlation patterns for each month shows that two periods (February–May, and September–November) are delimited by a period of great instability (December–January) and by the dry period (June–August). Three main rainfall regions can be distinguished, delimited and governed mainly by the topography and the coastal influence.

Composite correlation fields based on a 5-year record of daily rainfall at 67 stations throughout Tunisia were used to investigate spatial and temporal properties of rainfall fields. The composite correlation fields had in general banded or elliptical patterns and with the elongations generally along the coastline or the topographical ridges. The banded patterns occurred usually during the rainy season, and the elliptical patterns occurred toward the summer or early autumn. The ratio of width to length of the elongated correlation fields varied in general between 0.1 and 0.4. The composite correlation fields defined as the area within the 0.7 correlation isoline were usually less than about 8.000 km2. The mean monthly rainfall was moderately correlated with the size of the composite correlation fields. The major orientation of the coastline seems to be a more important factor for the rainfall generation than are local irregularities in the coastal orientation and local topographical differences.

Fifty-two double-ring infiltrometer tests, performed in a small, partly urbanized catchment in northern Tunisia are analyzed. Spatial variability is characterized by use of cross-correlation functions. Spatial patterns of infiltration properties are shown to be governed by geomorphology and occurring vegetation. Different geomorphological zones and zones with equal density of vegetation tend to be oriented in a parallel pattern in relation to the wadi. Statistical properties of infiltration capacities depending on geomorphological zone are presented.

In developing countries, the use of mathematical models in hydrological forecasting is increasing, making for optimal planning and management of water resources systems. Such application, however, faces different problems. One of these problems is that computers may not be available. Even if they are available, computer time is expensive. Hence, there is a need for simple models which can be run on pocket calculators or which are computer-time efficient, with high accuracy. This paper presents a rainfall-runoff model with a very simple structure. With simple algorithms, the model can be used with computers with small memory capacity. A method for estimating mean areal rainfall, representing the detailed distribution of rain over an area, is also put forward. The model has been applied to a small, mainly rural catchment in northern Tunisia for both single rainfall event simulation and continuous simulation for longer periods. The outcome was most encouraging. In the present paper the measured and ...

The infiltration equations according to Horton and Philip are applied to 52 double-ring infiltrometer tests performed in a small semiarid catchment in northern Tunisia. Spatial variability in infiltration properties is analysed as regards the coefficients of the two equations. Different geomorphological zones display different infiltration characteristics even if there is large variability within each zone and no clear statistical difference between the zones. Statistical properties of the coefficients of Horton's and Philip's equations describing cumulative infiltration are presented and discussed. The statistical distribution of the coefficients seems to be well approximated by an exponential function.

Aspects of spatial and temporal rainfall variability and rainfall analysis in relation to some water management problems are surveyed and discussed. It is concluded that relevant modelling of hydrological processes in which the rainfall is a driving force is vital with respect to possibilities of finding solutions to increasing environmental problems following urbanization and industrialization. However, modern computer methods and our knowledge of the spatial and dynamic properties of rainfall fields are seldom used in practical engineering applications. This causes errors and uncertainties in the calculated output. Bridging the gaps between researchers and engineers may overcome some of these problems. It is also argued that experimental studies in a variety of climates and physiographical conditions using an interdisciplinary approach are needed in order to further investigate the scale and dynamics of spatial rainfall variability.

The paper deals with the qualitative and quantitative characteristics of urban discharge. Ratios for urban discharge and recipient flow during different time intervals are presented and discussed. The quality of the urban discharge is illustrated through pollutographs.

Urmia Lake (also known as Oroumieh Lake) is a shallow terminal lake located in northwest Iran and one of the largest permanent lakes in the Middle East. Due to its biodiversity it has been designated as a Biosphere Reserve by UNESCO and a National Park under the 1971 Ramsar Convention. At present, the entire lake’s watershed is threatened due to drought and abrupt decline of the lake’s water level and the consequent increase of salinity. The rapidly declining eco-environmental conditions have serious impacts on the socio-economy of the whole region. In this paper we review the environmental state of art and suggest measures to improve the lake’s ecology by short- and long-term restoration possibilities. There are indications that the hydrology of the area could be described by a chaotic climate and a low-dimensional dynamical system. However, also the human impact is strong due to mismanagement of water resources. It is concluded that a multidisciplinary integrated approach is needed to tackle the current critical situation.

A noninvasive approach for measurements of near-surface water content (θ) and bulk electrical conductivity (σ a ) using time domain reflectometry (TDR) is presented. In this approach, an ordinary three-rod TDR probe is used together with a polyvinyl chloride (PVC) surface block that surrounds half the measurement volume. Theoretical and experimental results show that an analytical solution of the apparent dielectric constant K a and the σ of the soil is possible. Thus, the suggested technique does not require a separate calibration of the relationship between the measured effective K a and K a of the soil. The variability of the measurements was shown to be slightly higher than using the traditional approach. The spatial sensitivity of the suggested technique was also investigated. It was shown that using a three-rod TI)R probe with a rod spacing of 0.05 m allows the θ and σ a to be measured in the uppermost 2 cm of the soil.

Climate variability and climate change are of great concern to economists and energy producers as well as environmentalists as both affect the precipitation and temperature in many regions of the world. Among those affected by climate variability is the Scandinavian Peninsula. Particularly, its winter precipitation and temperature are affected by the variations of the so-called North Atlantic Oscillation (NAO). The objective of this paper is to analyze the spatial distribution of the influence of NAO over Scandinavia. This analysis is a first step to establishing a predictive model, driven by a climatic indicator such as NAO, for the available water resources of different regions in Scandinavia. Such a tool would be valuable for predicting potential of hydropower production one or more seasons in advance.