Spyros Giakoumakis | National Technical University of Athens (original) (raw)

Papers by Spyros Giakoumakis

Journal of Agricultural, Earth and Environmental Sciences, 2025

In this work a modified version of the well-known Simple Water Balance (SWB) model, comprising he... more In this work a modified version of the well-known Simple Water Balance (SWB) model, comprising here three parameters instead of one, was used. Although simple, the model was tested in large-scale river basins in east-central Greece, upstream two hydrometric stations. The available historic runoff records comprised 19 hydrologic years each, on a monthly basis. Thirteen among them were used for calibrating the model, whereas the six subsequent, for validating it. Two different efficiency criteria were used as a measure of performance of the modified model. Their values, calculated for both calibration and validation stages, were close and relatively high. Thus, keeping in mind both the size and complexity of the river basins studied, one can conclude that the modified model, despite its simplistic concept and lumped form, fits satisfactorily the historic runoff series.

Journal of Agricultural, Earth and Environmental Sciences , 2024

In this work, via Med basin software, two different conceptual rainfall-runoff models were used i... more In this work, via Med basin software, two different conceptual rainfall-runoff models were used i.e. a monthly time step modified simple water balance model (Medbasin-M) comprising three calibration parameters and a daily time step (Med basin-D) comprising 14 parameters. As study area was selected the mountainous Plasters lake river basin in Thessaly of a total area of 166 km2. Rainfall and potential evapotranspiration data were used as input to both models. Additionally, measured runoff values were available for performing calibration and validation stages. As calibration period for both models was chosen from October 2012 to September 2017 and as validation period from October 2017 to September 2019. The Medbasin-M with the three parameters was proved that performs satisfactorily (e.g. NSE equals 0.57 for calibration and 0.52 for validation period). Moreover, Med basin-D gave clearly better results: 1. for the simulated daily runoff (NSE 0.73 and 0.69 for calibration and validation periods respectively) 2. for the simulated monthly runoff (NSE equals 0.9 for calibration and 0.77 for validation period). In addition, a sensitivity analysis was carried out in each case, for indicating which parameters influence the most models output.

International Journal of Heat and Fluid Flow, Apr 1, 1994

Abstract A one-dimensional model is used for simulating coupled heat and mass transfers in a vert... more Abstract A one-dimensional model is used for simulating coupled heat and mass transfers in a vertical porous medium column, with the upper end subjected to a negative temperature. The model can predict accurately both temperature and total water content profiles along the column, provided that both heat- and mass-conversation equations are solved simultaneously. On the contrary, when only heat transfer equation is solved, the position of the moving freezing front (isothermal of 273.16°K), is systematically underestimated. Moreover, it was shown that the commonly used surface-tension viscous-flow theory for estimating the temperature-dependent soil hydraulic properties (i.e., matric potential versus liquid water content, h[Θ 1 ], and hydraulic conductivity versus liquid water content, K[Θ 1 ]), when combined with the model, fails to describe satisfactorily the evolution of the freezing process.

Water Resources Management, 1992

The main objective of this paper is to review the existing methodologies for the estimation and a... more The main objective of this paper is to review the existing methodologies for the estimation and analysis of regional drought. As a first step, point drought methods are presented. Further emphasis is given to the definition and estimation of regional drought characteristics. Stochastic processes for simulating the time-space variability of drought, are presented. Finally, illustrative examples are shown and recommendations for further research are given.

Journal of Hydrology, Dec 1, 1991

The effect of temperature in soil-water transfer studies is usually neglected. However, experimen... more The effect of temperature in soil-water transfer studies is usually neglected. However, experimental research has shown that there is a strong temperature effect on the characteristic soil hydraulic functions. such as the matric potential versus water content relationship, h(0), and the hydraulic conductivity versus water content relationship, K(O). The objective of this study was to examine whether this effect can be isolated and explained. For this purpose, experimental h(O) and K(O} values from two different sandy soils at temperatures of 20, 8 and 3°C, were directly compared with predictions obtained by both the surface-tension viscous-flow model of soil moisture movement (STVF) and the empirical Gain factor model extended to include the K(O) relationship. Results showed that the predictive efficiency of the STVF method depends upon the soil type. For fine-textured material the Gain factor model seemed to perform satisfactorily. Finally, it was shown that unique normalized functions of both characteristic soil hydraulic properties, independent of temperature, can always be obtained.

In this article a modified version of the Simple Water Balance (SWB) model, comprising here three... more In this article a modified version of the Simple Water Balance (SWB) model, comprising here three parameters instead of one, was used. The modified model was tested in large-scale river basins in east-central Greece, upstream two hydrometric stations. The available historic runoff records comprised 19 hydrologic years each, on a monthly basis. Thirteen among them were used for calibrating the model, whereas the six subsequent, for validating it. Two different efficiency criteria were used as a measure of performance of the modified model. Their values, calculated for both calibration and validation stages, were close and relatively high. Thus, keeping in mind both the size and complexity of the river basins studied, one can conclude that the modified model, despite its lumped form, fits satisfactorily the historic runoff series.

During the last decades, numerous rainfall-runoff models have been developed, incorporating vario... more During the last decades, numerous rainfall-runoff models have been developed, incorporating various levels of complexity. However, the choice of the proper model remains a challenging task, especially in arid or semi-arid climates such as the Mediterranean, and in cases of limited data availability. In such cases, the use of simple rainfallrunoff models may be still the most suitable approach. In this study, a modified version of the well-known Simple Water Balance (SWB) model is presented. The modified SWB model comprises three calibration parameters instead of one, though it retains the simple structure of the original model. The model was evaluated in two regions of Greece with different Mediterranean climatic conditions (Acheloos and Pinios river basins). The available historic runoff series comprised 19 hydrologic years each, on a monthly basis. Thirteen among them were used for calibrating the model, whereas the six subsequent, for validating it. Two evaluation criteria were u...

In the present study a new approach for planning Micro-Catchment Water Harvesting (M.C.W.H.) syst... more In the present study a new approach for planning Micro-Catchment Water Harvesting (M.C.W.H.) systems for irrigation in semi-arid regions such as the Aegean islands, is presented. This is a cheap solution for constructing infrastructure with zero energy cost in regions where water is scarce. The proposed approach introduces simple linear relationships for estimating the annual volume of water Vs collected mainly from the CA (Contributing Area), stored in the root zone (Infiltration Basin, IB), according to the annual rainfall and runoff depths, after having determined the ratio of areas of micro-catchment components, i.e., λ = ΑCA/ΑΙΒ and its whole area AMC This procedure was applied in Paros island of the Cyclades complex in the middle of the Aegean sea in east Mediterranean. Besides, income-cost analysis was performed via NPV method for almonds, peach and apricot trees.

This study introduces a continuous simulation model dealing with the reconnaissance estimation of... more This study introduces a continuous simulation model dealing with the reconnaissance estimation of sediment yield from a hydrological basin. Based on this model, historical precipitation data of the Mornos River Basin in western Greece, were analyzed. The analysis allowed to establish a relationship between meteorological drought and sediment yield through a dimensionless erosion index. It was indicated that, for the historical precipitation series considered, sediment yield estimations were higher during the wet period following a period of drought.

Laboratory experiments were conducted for determining hydraulic conductivity during infiltration ... more Laboratory experiments were conducted for determining hydraulic conductivity during infiltration in an unsaturated sandy loam soil, using both steady state and equilibrium methods. A constant head Guelph permeameter and a volumetric pressure plate extractor were used. Based on two ponded heights in the permeameter, the parameters of Gardner's equation expressing the unsaturated hydraulic conductivity as a function of pressure head (i.e. the saturated hydraulic conductivity K s and the exponent α), were estimated simultaneously. Furthermore, it was found that the parameter α, could also be predicted from the soil-water retention curve based on equilibrium data obtained from the extractor. This indicated that, for the soil type studied, one-ponded height in the permeameter method could be sufficient for the determination of the exponent α, provided that the soil-water retention curve is known.

Water Resources Management, 2001

A series of laboratory experiments was carried out on a sandy loam soil, for testing the predicti... more A series of laboratory experiments was carried out on a sandy loam soil, for testing the predictive ability of a linearized analytical solution of the kinematic wave equation used for runoff estimation in micro-catchment water harvesting design. The experimental set-up comprised an inclined flume containing the soil sample and a rainfall simulator. The flume represented the Contributing Area (CA) of

Journal of Hydrology, 1991

Arabian Journal of Geosciences, 2014

ABSTRACT Soil salinization is an environmental problem having significant impacts on the soil–wat... more ABSTRACT Soil salinization is an environmental problem having significant impacts on the soil–water–plant system. This problem is more frequent in coastal areas due to seawater intrusion into the land. Assessing the soil salinization is a critical issue for the agricultural areas situated in the Mediterranean basin. This paper examines the deterioration of soil quality in the cultivated land of a Mediterranean site (Agoulinitsa district—West Greece). Soil samples were collected in both pre-irrigation and post-irrigation seasons. Electrical conductivity (EC), pH and the ions Br−, Ca2+, Cl−, F−, K+, Li+, Mg2+, Na+, NH4 +, NO2 −, NO3 −, PO4 3− and SO4 2− were determined by the 1:2 (soil/water ratio on weight basis) method. The salts which were present in both seasons in the soils of the area studied are KCl, MgCl2, NaCl, CaSO4 and K2SO4. The wide spatiotemporal variation of EC in the cultivated land in both seasons demonstrates that soil salinity is controlled mainly by seawater intrusion and anthropogenic factors such as the application of salt-rich water which is directly pumped from the drainage ditches. Seawater intrusion provides the affected soil with elevated contents of Ca2+, Cl−, K+, Mg2+, Na+ and SO4 2−. Classification of the soils by using criteria given by the literature is discussed. Practices to prevent, or at least ameliorate, salinization in the cultivated land of Agoulinitsa district are proposed.

In this work, simulation of the operation of the Plastiras reservoir for a 58-year period (from 1... more In this work, simulation of the operation of the Plastiras reservoir for a 58-year period (from 1961-62 to 2018-19), was performed. Different demand scenarios, comprising both irrigation and water supply, were examined. Due to the over-abstraction of water from the reservoir, especially for irrigating agricultural land in the plain of Thessaly during the dry summer period, the water level of the reservoir is often lowered dangerously, threatening so its sustainability. Taking into account that over 90% of water uptake from the reservoir is for irrigation purposes, it was shown that this quantity can be reduced drastically and, thus, the probability of failure of the reservoir turns out to be negligible, provided that the existing open channel irrigation network in the area is replaced by drip irrigation systems, saving important quantities of fresh water from the reservoir, increasing so the water efficiency for agriculture (efficiency coefficient for drip irrigation can reach up to...

Water Science and Technology: Water Supply

The disposal of the excessive volume of degraded water coming from agricultural drainage systems ... more The disposal of the excessive volume of degraded water coming from agricultural drainage systems is a serious environmental and economic issue, since a significant load of agrochemicals and salts contaminates water bodies downstream. An integrated on-farm drainage management (IFDM) system is an effective method of treatment by successively irrigating zones with drainage water. Each zone is cultivated with crops that have increasing tolerance to salinity, so that the drainage water effluents are minimized to an extent that the final drainage water volume is collected into an evaporation pond. The methodology of the system is proposed herein for a regional irrigationdrainage network (E1 in Agoulinitsa irrigation district in western Greece) as a method of reducing the disposal of agrochemicals in the coastal environment. Based on the design principles of an IFDM system, both the surface area of every irrigation zone and the costs of installing and operating the system are assessed. A scenario regarding the volume of drainage water that must be treated is examined as a sensitivity analysis. The results show that almost 15% of the cultivated area must be bounded for non-productive uses, resulting in a significant economic impact on the net present value of the investment.

Earth Sciences Research Journal