Torrent

A new one-dimensional (1-D) numerical model for calculating flow and sediment transport in steep mountain streams is developed. 3 ST1D, which stands for Steep Stream Sediment Transport 1-D model, is applicable to unsteady flow conditions that occur over transcritical flow stream reaches such as flows over step-pool sequences. 3ST1D consists of two coupled components, the hydrodynamic and the sediment transport. The flow component is addressed here by solving the unsteady form of the Saint-Venant equations. The Total Variation Diminishing Dissipation (TVD)-MacCormack scheme, which is a shock-capturing scheme capable of rendering the solution oscillation free, is employed here to approximate the hydrodynamic solution over transcritical flow stream reaches. The sediment component of the model accounts for multifractional sediment transport and incorporates a series of various incipient motion criteria and frictional formulas applicable to mountain streams. In addition, sediment entrainability is estimated based on a state-of-the art formula that accounts for the bed porosity, turbulent bursting frequency, probability of occurrence of strong episodic turbulent events, and sediment availability in the unit bed area. The model at the end of each time step predicts the flow depth, velocity and shear stress distribution within a cell and calculates changes in bed evolution and grain size distribution. The overall performance of the model is evaluated by comparing its predictions with observations from two flume studies, two field investigations and against the predictions of the quasi-steady model of Lopez and Falcon developed for mountain streams. A sensitivity analysis is performed to assess the effects of cell size and Manning’s roughness coefficient in the predictive ability of the model.Un nouveau modèle numérique uni-dimensionnel (1-D) de calcul d’écoulement et de transport de sédiment dans les torrents rapides de montagne a été développé: 3ST1D, mis pour Steep Stream Sediment Transport 1-D model (modèle de transport 1-D de sédiment dans les torrents à forte pente), est applicable aux écoulements instationnaires qui se produisent dans les biefs critiques tels que les séquences de marches. 3ST1D se compose de deux composantes couplées, l’hydrodynamique et le transport de sédiment. Pour la composante écoulement on a recours à la forme instationnaire des équations de Saint-Venant Le schéma TVD de MacCormack (diminution de la variation totale de dissipation) qui est un schéma absorbant les chocs capable de rendre la solution libre d’oscillations, est utilisé pour approcher la solution hydrodynamique dans les biefs du torrent où l’écoulement est transcritique. La composante de sédiment du modèle tient compte de sédiments composites et incorpore une série de critères pour le début d’entraînement et de formules de frottement applicables aux torrents de montagne. En outre, l’entraînement de sédiment est basé sur l’état de l’art qui tient compte de la porosité de lit, de la fréquence des bouffées turbulentes, de la probabilité d’occurrence d’événements turbulents épisodiques forts, et de la mobilité des sédiments dans le secteur de lit. Le modèle à la fin de chaque pas de temps donne la profondeur, la distribution de vitesse et de contraintes de cisaillement dans une cellule et calcule l’évolution du lit et de la distribution des tailles de grains. La performance globale du modèle est évaluée en comparant ses prévisions aux observations de deux études en canal, de deux expériences en nature et des prévisions du modèle quasi-stationnaire de Lopez et de Falcon développé pour des torrents de montagne. Une analyse de sensibilité est exécutée pour évaluer les effets de la taille de maille et du coefficient de rugosité de Manning sur les capacités prédictives du modèle.

Torrent flood origin from the mountain, but consequences felt in the downstream sections.  River basins are dynamic systems constituted by a complex arrangement of fluxes between the land and water environment. Land use pattern and planning has a observed influence on pick flow and sediments in small catchments. Case study was carried out on a Sushica and Radoviska Reka floods in December 2008. Damages by torrent Sushica were significant and much higher then Radoviska Reka damages. The aim of this study is to defined impact of geospatial factors on appearance of the flood wave and on the damages. A digital landscape model was developed consist of several layers needed for: analyze of discharge (DEM, slope, soil, geology, land cover/use, erosion, precipitation intensity), layers for analyze of reason for damages (urban plan, position of critical facilities, hydraulic structures in the bed, bridges) and analyze of municipality crises management body operation. Basin of Sushica (18,7km2) is smaller then Radoviska Reka (53,8 km2). All natural factors (slopes, drainage net, altitude difference, soil, geology, basin area..) contribute to the fact that Radoviska Reka is much more dangerous. Land cover favor Sushica (consist of arable land, degraded pastures and transitional woodland) while in the Radoviska Reka basin more then a half of the area is forest. Gavrilovic model was used for quantification of natural factors impact.  Erosion coefficient is almost double higher in Sushica (Z=0,65) then in Radoviska Reka (Z=0,35). Precipitation value on critical day was 52,5 mm. Radoviska Reka was trained with various hydraulic structures (longitudinal and cross structure - check-dams for sediment retention etc.) Otherwise, there isn’t any type of structure in Sushica bed. Urban plan in the center of the city (where Radoviska Reka pass) is adequate for flood damages minimizing, because there are two streets along the river bed that enable open corridor.. But the main problem for flooding was closure of the bed profile with sediment and improper built bridges (on the “Ancient Bridge” profile was 40% closed). Flood water didn’t contain significant amount of sediments. Urban structure in the industrial part (where Sushica pass) was not adequate. There are installations closed to the torrent bed and these objects were highly damaged. As a result of, high erodibility of the basin and existence of wild landfill, significant amount of sediments closed the bridges, the first bridge collapsed, sediment was re-transported to the second bridge that was totally closed and water jump over the bridge and damaged infrastructure facilities.  Municipality body for crises management operated but after the flood according to the national legislation and principles. Early warning system was not established but because of speed of onset of this hazard, practically there was no time for warning the citizens. It can be concluded that the main reason for flooding of the center by Radoviska Reka was improper bridges, while land cover/use pattern and erosion intensity together with the inadequate set up of industrial object and absence of flood control structures result in flood wave that cause significant damages.

In the complex of tasks required to design various hydraulic structures, the estimation of maximum water discharge (peak flow) with different returning period, for ungauged basins is one of the most difficult ones, and could be the key problem and a base of other estimations and further designing. Understanding the accuracy of commonly used methods for estimating peak stream flows is important because the designs of bridges, culverts, and other river structures are based on these flows. There are a lot of known empirical methods in use spread all over the world. Some of them are only for local use, but some methods are to be universal, but calibration on local conditions before use is required. SCS method is one of the most spread. The origin and evolution of the USDA SCS curve number method for estimating runoff from small ungauged rural catchments is traced. The purpose of this paper is to test theoretical applicability of SCS method for small basin peak flow estimation in Macedonian conditions. !% probability Peak flow was done on 30 small torrents and 2 additional methods (Concentration time, Gavrilovic method) were used for compassion. Results got by SCS method were lower then other. Then was tested all range of CN compared with effective precipitation (Pe). Values for effective precipitation were maximal estimated for Macedonian conditions (8 pluviographic gauge stations)  by Skoklevski & Todorovski. This analyze show that through crossing Tk (time of concentration), suitable precipitation values for it (Pe) and CN could be got some illogical and practically unreal results in a pat of the range of CN. It depend on the value of CN. It showed limited applicability of this method.

Soil erosion has been occurring over the geological time. Inappropriate human activities
accelerate this process. Soil erosion by water is a widespread problem throughout Europe.
The South and Southeast regions of Europe are significantly prone to water erosion. In parts
of the region, erosion has reached a stage of irreversibility and in some places erosion has
practically ceased because there is no soil left. Scientists from the Balkan countries faced with
the erosion problem for years, paid significant attention to solving problems with erosion. The
aim of this study is to compare the results of water erosion intensity in the Balkan countries
with other European countries. The basic methodological approach in this paper is an analysis
of secondary data, using the method of “content analyses” of various data sources. Inductive
and deductive qualitative analysis was used and finally the method of “comparative analysis” is
applied too. Through the analysis of national researches, it was estimated that erosion intensity
in Balkan countries is 548 m3km-2 (similar to 5.48 tha-1) and the total amount of annual produced
erosive material is 419.9*106 m3. The mean European average annual erosion intensity is
3.13tha-1. The most erosive countries in Europe are the Balkan countries, Albania and Montenegro
where the mean annual intensity of erosion is > 10 tha-1.

Mountain risk and disaster management (MRDM) in the field of natural hazards is in alpine countries a national task. Natural hazards in alpine spaces are represented by floods, avalanches, landslides, rock falls and debris flows. MRDM is a very complex system which includes many technical and administrative components. In Austria MRDM is based on legal acts and regulations enforced by different federal political levels. At national level Austrian Federal Ministry of Agriculture, Forestry, Environment andWater Management and Austrian Service for Torrent and Avalanche Control are responsible for MRDM. A big desire of all involved participants in MRDM is to get handy solutions in this complexity. Since 1975 Austrian Service for Torrent
and Avalanche Control has to keep a torrent and avalanche cadaster (TAC). First TAC was held just analog but with geographic information systems (GIS) it was possible to create since 2004 a digital TAC. The digital TAC is diverted into different modules: torrent areas, avalanche areas, hazard zone maps, etc. Each module has its own character and own workflow for digitizing new objects, the modules act also interactive. For public information supply objects can be exported from the digital TAC. Only when technical and legal work of an object is correct it can be send through a data tunnel to GIS portals with permanent public access for further public use. This paper gives a basic insight into the digital TAC supported by GIS which is used in the offices of Austrian Service for Torrent and Avalanche Control.

We present a method to estimate Time of Concentration (T c) and Storage Coefficient (R) to develop Clark’s Instantaneous Unit Hydrograph (CIUH). T c is estimated from Time Area Diagram of the catchment and R is determined using optimization approach based on Downhill Simplex technique (code written in FORTRAN). Four different objective functions are used in optimization to determine R. The sum of least squares objective function is used in a novel way by relating it to slope of a linear regression best fit line drawn between observed and simulated peak discharge values to find R. Physical parameters (delineation, land slope, stream lengths and associated drainage areas) of the catchment are derived from SPOT satellite imageries of the basin using ERDAS: Arc GIS is used for geographic data processing. Ten randomly selected rainfall–runoff events are used for calibration and five for validation. Using CIUH, a Direct surface runoff hydrograph (DSRH) is developed. Kaha catchment (5,598 km2), part of Indus river system, located in semi-arid region of Pakistan and dominated by hill torrent flows is used to demonstrate the applicability of proposed approach. Model results during validation are very good with model efficiency of more than 95% and root mean square error of less than 6%. Impact of variation in model parameters T c and R on DSRH is investigated. It is identified that DSRH is more sensitive to R compared to T c. Relatively equal values of R and T c reveal that shape of DSRH for a large catchment depends on both runoff diffusion and translation flow effects. The runoff diffusion effect is found to be dominant.