Konstantinos X. Soulis

Identification of the SCS-CN Parameter Spatial Distribution Using Rainfall-Runoff Data in Heterogeneous Watersheds

The Soil Conservation Service Curve Number (SCS-CN) method is widely used for predicting direct runoff volume for a given rainfall event. However, previous results indicated that when the CN value is determined from measured rainfall-runoff data in a natural watershed it is not possible to attribute a single CN value to the watershed, but actually the calculated CN values vary systematically with the rainfall depth. In a previous study, the authors investigated the hypothesis that the observed correlation between the calculated CN value and the rainfall depth in a watershed reflects the effect of the inevitable presence of soil-cover complex spatial variability along watersheds. In this study, a method to determine SCS-CN parameter values from rainfall-runoff data in heterogeneous watersheds is proposed. This method exploits the observed correlation between the calculated CN values and the rainfall depths in order to identify the spatial distribution of CN values along the watershed taking in to account the specific characteristics of the watershed. The proposed method utilizes the available rainfall-runoff data, remote sensing data and GIS techniques in order to provide information on spatial watershed characteristics that drive hydrological behavior. Furthermore, it allows the estimation of CN values for specific soil-land cover complexes in more complex watersheds. The proposed method was tested in a small experimental watershed in Greece. The watershed is equipped with a dense hydro-meteorological network, which together with a detailed land cover and soil survey using remote sensing and GIS techniques provided the detailed data required for this analysis.

Potential impacts of climate change on flow regime and fish habitat in mountain rivers of the south-western Balkans

The climate change in the Mediterranean area is expected to have significant impacts on the aquatic ecosystems and particular in the mountain rivers and streams that often host important species such as the Salmo farioides, Karaman 1938. These impacts will most possibly affect the habitat availability for various aquatic species resulting to an essential alteration of the water requirements, either for dams or other water abstractions, in order to maintain the essential levels of ecological flow for the rivers. The main scope of this study was to assess potential climate change impacts on the hydrological patterns and typical biota for a south-western Balkan mountain river, the Acheloos. The altered flow regimes under different emission scenarios of the Intergovernmental Panel on Climate Change (IPCC) were estimated using a hydrological model and based on regional climate simulations over the study area. The Indicators of Hydrologic Alteration (IHA) methodology was then used to assess the potential streamflow alterations in the studied river due to predicted climate change conditions. A fish habitat simulation method integrating univariate habitat suitability curves and hydraulic modeling techniques were used to assess the impacts on the relationships between the aquatic biota and hydrological status utilizing a sentinel species, the West Balkan trout. The most prominent effects of the climate change scenarios depict severe flow reductions that are likely to occur especially during the summer flows, changing the duration and depressing the magnitude of the natural low flow conditions. Weighted Usable Area-flow curves indicated the limitation of suitable habitat for the native trout. Finally, this preliminary application highlighted the potential of science-based hydrological and habitat simulation approaches that are relevant to both biological quality elements (fish) and current EU Water policy to serve as efficient tools for the estimation of possible climate change impacts on the south-western Balkan river ecosystems.

Development of a GIS-based Spatially Distributed Continuous Hydrological Model and its First Application

Abstract This study describes the development of a spatially distributed continuous hydrological model and its application on an Aegean Sea island. This model was developed on the basis of a Geographical Information System (GIS) in direct interaction with the special database containing the input data in a spatially distributed form. The model is physically based; it can evaluate the daily values of the water balance components in very fine spatial resolution and gives relatively accurate results with small calibration effort. The main scope of the model is to utilize a valuable tool in areas with great scarcity of hydrometric data, increased water needs and serious shortages of fresh water. The model was applied on Naxos, a medium size Aegean island, with satisfactory results.

Performance Analysis and Calibration of a New Low-Cost Capacitance Soil Moisture Sensor

AbstractSeveral newly developed sensors based on capacitance and frequency techniques have simplified real-time determination of soil water content (θ). The 10HS sensor is one of the most recent developments in capacitance sensors. However, up to now, little is known about the accuracy of this sensor, and the dependency of its measurements on soil type and environmental factors. In this study, the performance of the 10HS sensor was investigated through experiments using liquids with known dielectric properties and experiments in a set of porous media exhibiting a wide range of properties. The response of the 10HS sensor in bilayered systems was also investigated. The experimental results suggested that there is a distinct instrument sensitivity to soil type, indicating the need for individual soil calibration. A set of specific calibration equations for the various porous materials studied were proposed. It was shown that the 10HS sensor is able to provide reasonably accurate relative permittivity (er) me...

Development of a simplified grid cells ordering method facilitating GIS-based spatially distributed hydrological modeling

In many spatially distributed hydrological models the watershed is discretized into grid cells each of which represents an area with average properties. The hydrological response of these cells is flowing downhill from one cell to other neighboring cells until it reaches the specified outlet. However, in these models the computations should proceed in correct hydrological sequence. In this study, an alternative simplified grid cells ordering method, facilitating GIS-based spatially distributed hydrological modeling, is presented. The proposed method utilizes recent developments on the analysis of grid-based terrains to serialize the grid cells of the studied area to a single thread representing a proper hydrologic cascading system. The main advantage of this new method is that it is very simple, but at the same time efficient. Furthermore, the resulted ordered sequence of cells can be accessed serially in a single pass for each time step, enhancing the performance and simplifying the implementation of hydrological models.

Rapid Graphical Detection of Weakness Problems in Numerical Simulation Infiltration Models Using a Linearized Form Equation

Recently, Valiantzas proposed a new two-parameter vertical infiltration equation that can be transformed to a linearized-form equation that essentially states that the shape of the cumulative infiltration data, when presented in the form of (i2/t) versus i, is linear. In this paper, the presentation of the numerical data to the Valiantzas linearized-form equation is proposed as an additional criterion to detect easily and rapidly possible errors of the numerical solutions and eventually to choose the best spatial discretization for a simulated infiltration event that is used as setup parameter to the numerical infiltration models. Numerical data and analytical solutions were used to validate the proposed method.

Comparative Assessment of Environmental Flow Estimation Methods in a Mediterranean Mountain River

The ecological integrity of rivers ultimately depends on flow regime. Flow degradation is especially prominent in Mediterranean systems and assessing environmental flows in modified rivers is difficult, especially in environments with poor hydrologic monitoring and data availability. In many Mediterranean countries, which are characterized by pronounced natural variability and low summer flows, water management actions usually focus on prescribing minimum acceptable flows estimated by hydrologic methods. In this study, a comparative assessment of environmental flow estimation methods is developed in a river with poorly monitored flows and limited understanding of past reference conditions. This assessment incorporates both a hydrologic and a fish habitat simulation effort that takes into consideration hydrologic seasonality in a Greek mountainous river. The results of this study indicate that especially in data scarce regions the utilization of biotic indicators through habitat models, may provide valuable information, beyond that achievable with hydrologic methods, for developing regional environmental flow criteria. Despite the widespread use of the method, challenges in transferability of fish habitat simulation provide undefined levels of uncertainty and may require the concurrent use of different assessment tools and site-specific study.

Modified Form of the Extended Kostiakov Equation Including Various Initial and Boundary Conditions

The extended Kostiakov equation is intensively used in surface irrigation applications. Traditionally, the extended Kostiakov infiltration formula is calibrated for specific field conditions. However, there is a dependence of the extended Kostiakov coefficients on both initial and boundary conditions. In this paper, a new simplified methodology is developed to account extended Kostiakov κ variation for these effects. The purely empirical extended Kostiakov equation is transformed to a form of a modified version of the classical Philip two-term equation. This modification relates a physical parameter, the soil sorptivity S, with the purely empirical coefficient κ of the extended Kostiakov formula. Then, the variation of the sorptivity S for various water levels and initial water contents is given theoretically by a simple algebraic equation. The proposed correction was compared with numerical infiltration data with varying initial (water content) and boundary conditions (ponding depth) for two contrasting soils. Results indicate that the corrected infiltration curves converge well with the simulated ones.

Field Calibration of Weirs Using Partial Volumetric Flow Measurements

AbstractA simple and low-cost flow-measurement method for the field calibration of weirs is described. With this method, accurate estimations of the flow rate over a weir can be made on the basis of volumetric flow measurements of a fraction of the total flow, using common equipment. Two variants of the method, suitable for the calibration of rectangular or auxiliary profiled weirs, are described. The method, under specific conditions, can be also used for the field calibration of other flow-measurement or irrigation structures.

Estimation of SCS Curve Number variation following forest fires

ABSTRACT The Soil Conservation Service Curve Number (CN) method is routinely used to estimate the effects of forest fires on hydrological response. However, despite recent efforts, CN values are still not well known for burned conditions. A major forest fire in Attica, Greece, which affected the Lykorrema stream experimental watershed, provided an opportunity for the estimation of post-fire CN variation using detailed pre-fire and post-fire rainfall–runoff datasets. The CN values for both periods were estimated and compared using a wide range of available methods. Methods considering the spatial variability of soil-cover complexes were also used to investigate the effect of spatial heterogeneity. The post-fire watershed response changed from complacent to standard. Direct runoff depths and peak flows increased by a factor of more than 7.7 and 11.8, respectively. On average, the estimated post-fire CN values for the studied soil-cover complexes increased by about 25 units. This study may assist the improvement of existing post-fire hydrological assessment tools.