Oliver Horvat

The limitations of assessing impacts of land use changes on runoff with a distributed hydrological model: case study of the Hron River

A distributed hydrological model was applied for estimating changes in a runoff regime due to land use changes. The upper Hron river basin, which has an area of 1766 km2 and is located in central Slovakia, was selected as the pilot basin. A physically-based rainfall-runoff model with distributed parameters was used for modelling runoff from rainfall and melting snow. The parameters of the model were estimated using climate data from 1981–2000 and from three digital map layers: a land-use map, soil map and digital elevation model. Several scenarios of changes in land use were prepared, and the runoff under the new land use conditions was simulated. Long-term mean annual runoff components and the design maximal mean daily discharges with a return period from 5 to 100 years under the previous and changed land uses were estimated and compared. The simulated runoff changes were confronted with expert judgments and estimates from the literature. Limitations of the use of distributed models for estimating land use changes are discussed.

Post-event analysis and flash flood hydrology in Slovakia

Abstract This work examines the main features of the flash flood regime in Central Europe as revealed by an analysis of flash floods that have occurred in Slovakia. The work is organized into the following two parts: The first part focuses on estimating the rainfall-runoff relationships for 3 major flash flood events, which were among the most severe events since 1998 and caused a loss of lives and a large amount of damage. The selected flash floods occurred on the 20th of July, 1998, in the Malá Svinka and Dubovický Creek basins; the 24th of July, 2001, at Štrbský Creek; and the 19th of June, 2004, at Turniansky Creek. The analysis aims to assess the flash flood peaks and rainfall-runoff properties by combining post-flood surveys and the application of hydrological and hydraulic post-event analyses. Next, a spatially-distributed hydrological model based on the availability of the raster information of the landscape’s topography, soil and vegetation properties, and rainfall data was used to simulate the runoff. The results from the application of the distributed hydrological model were used to analyse the consistency of the surveyed peak discharges with respect to the estimated rainfall properties and drainage basins. In the second part these data were combined with observations from flash flood events which were observed during the last 100 years and are focused on an analysis of the relationship between the flood peaks and the catchment area. The envelope curve was shown to exhibit a more pronounced decrease with the catchment size with respect to other flash flood relationships found in the Mediterranean region. The differences between the two relationships mainly reflect changes in the coverage of the storm sizes and hydrological characteristics between the two regions.

Methodology for post-event analysis of flash floods - Svacenický Creek case study

Methodology for post-event analysis of flash floods - Svacenický Creek case study In this paper a methodology for a post-event analysis of a flash flood and estimation of the flood peak and volume are developed and tested. The selected flash flood occurred on the 6th of June, 2009 in the Svacenický Creek Basin. To understand rainfall-runoff processes during this extreme flash flood, the runoff response was simulated using the spatially-distributed hydrological model KLEM (Kinematic Local Excess Model). The distributed hydrological model is based on the availability of raster information about the landscapes topography, soil and vegetation properties and radar rainfall data. In the model, the SCS-Curve Number procedure is applied to a grid for the spatially-distributed representation of the runoff-generating processes. A description of the drainage systems response is used to represent the runoffs routing. The simulated values achieved by the KLEM model were comparable with the maximum peak estimated on the basis of the post-event surveying. The consistency of the estimated and simulated values from the KLEM model was evident both in time and space, and the methodology has shown its practical applicability.

Application of the Frier Distributed Model for Estimating the Impact of Land use Changes on the Water Balance in Selected Basins in Slovakia

Application of the Frier Distributed Model for Estimating the Impact of Land use Changes on the Water Balance in Selected Basins in Slovakia In this study, the FRIER rainfall-runoff model with distributed parameters was developed to assess changes in runoff and water balance due to changes in land use and climate. The water balance was calculated at 3 levels: on the surface and in unsaturated and saturated zones. Six basins from the central and eastern parts of Slovakia were selected on the basis of their similar size, but different topography, land use, soil texture and climate: the upper Hornád, the upper Hron, the Poprad, the Rimava, the Slaná and the Torysa River basins. Model parameters were estimated using data from the period from June 1998 to May 2000 in daily time steps. The differences and similarities of the hydrologic processes in individual basins were investigated during the calibration period. Several scenarios of changes in land use and two simple scenarios of changes in climate were developed to estimate the impact of these changes on water balance and runoff. The changes in the hydrological regime were compared and discussed. Využitie hydrologického modelu FRIER s priestorovo rozčlenenými parametrami na posúdenie vplyvu zmeny využitia územia na hydrologickú bilanciu vybraných povodí na Slovensku V posledných rokoch sa veľmi často hodnotia a diskutujú vplyvy zmien využitia krajiny a klímy na procesy hydrologickej bilancie, aj keď miera ich vplyvu na hydrologický režim sa najmä pre komplexnosť týchto procesov veľmi ťažko kvantifikuje. Na odhad vplyvu zmien využitia krajiny a klímy na odtok a zložky hydrologickej bilancie bol vyvinutý zrážkovo-odtokový model FRIER s rozčlenenými parametrami. Na základe podobnej veľkosti, ale rôznej topografie, využitia krajiny a pôdnej štruktúry bolo vybraných šesť pilotných povodí: povodie horného Hornádu, horného Hrona, Popradu, Rimavy, Slanej a Torysy. Parametre modelu boli kalibrované pre obdobie jún 1998 - máj 2000 v dennom časovom kroku. Na základe simulácií hydrologickej bilancie pre súčasný stav sa hodnotili rozdiely a podobnosti procesov tvorby odtoku v jednotlivých povodiach. Odtok a zložky hydrologickej bilancie boli následne simulované pre sedem scenárov zmien využitia krajiny a dva jednoduché scenáre zmeny zrážok a teploty vzduchu. Zmeny odtoku a hydrologickej bilancie boli porovnané a diskutované.

SCENARIOS OF FLOOD REGIME CHANGES DUE TO LAND USE CHANGE IN THE HRON RIVER BASIN

Possible changes in the flood regime of the Hron river basin due to land use change were estimated by using a physically based distributed rainfallrunoff model for modelling runoff from rainfall and snowmelt. Model parameters were estimated from data from the 1981-2000 period and three basic digital map layers: land use map, soil map and digital elevation model. Several scenarios of land use change were prepared and runoff under different land use conditions was simulated. Design maximum mean daily discharges with the return period of 100 years under current and changed land use were estimated and compared.