ON SOME MOUNTAIN STREAMS AND RIVERS MORPHODYNAMICAL PARAMETER CHARACTERISTICS USING FIELD AND NUMERICAL MODELING EXAMPLES WOJCIECH BARTNIK, LESZEK KSIĄŻEK, ARTUR RADECKI-PAWLIK, ANDRZEJ STRUŻYŃSKI Departament of Water Engineering, Agricultural University of Cracow, 30-059 Cracow, Al. Mickiewicza 24-28, Polan, rmbartni@cyf-kr.eu.pl 1. INTRODUCTION The work present work concentrates on escription of some basic parameters an features of the mountainous streams which are responsible for morphoynamical changes in a chosen cross section of it. The paper eals firstly with escription of the parameters of seiment motion in stream an the critical conitions of motion basically with the incipient of the motion of seiment, next is escribing some features from the mountainous gravel river be which one can fin in the fiel an finally the paper is showing a possibility of moeling the mentione phenomena using the case stuy results from one of Polish mountain rivers. 2. MOUNTAIN STREAMS BEDLOAD INCIPIENT MOTION AND BEDLOAD TRANSPORT OUTLOOK The comparison of beloaovement in mountain an lowlan streams an rivers inicates many ifferences. The lowlan rivers beloa transportation is an instant process. The beforms appear an reflect the flow conitions. They consists of very fine material. The be stability becomes a function of beloa transport intensity. The mountain river characterizes much more coarse material (fractions up to 0.2-0.3 m. Transportation of beloaaterial appears much less frequently in comparison to lowlan rivers. Many scientists escribe complicate phenomenon of coarse beloa transportation material. The most known are Einstein [1950], Shiels [1936], Yalin [1977], Bagnol [1986], Mayer-Peter an Müller [1948], Wang [1997], Sentürk [1977], [Gessler 1970], Parker [1990], Zanke [1992] anany more. The incipient motion epens on grain size, shape an a composition of multifraction layer covering the be surface. The sorting, sheltering an armoring processes become very important for transportation parameters. On the other sie, these processes influence the flow roughness parameters. Among others parameters for incipient motion an beloa transport shear stresses are the most important. The critical stresses characterizing the incipient motion of a granulometry change ue to the sheltering of fine fractions which can be escribe using Wang equations: ϵ 1 =1.786( 0.947 i - i / < 0.4 (1 ϵ 2 =( i 0.314 - i / 0.4 (2 where: mean iameter, i iameter of fraction i, hiing factor
Derivation between movement an no movement of every separate fraction can be escribe by using Shiels parameter: fi cr i, fi. (3 f m where: f i Shiels parameter for fraction i, f m Shiels parameter for mean iameter, cr critical sheer stresses, specific weight of submerge gravels. Equations 1, 2 an 3 allow for calculating Shiels parameter separately for fine an rough fractions. Below is presente the moifie Wang equation by Bartnik [1992]: f m1 i f 0.6 1 = m 1.786( 1 i 0.947 (4 i f 0.6 2 = f m2 m ( (5 0.314 1 The parameters f 1 an f 2 can be calculate using moifie Bartnik s equations: i 0.6 f m1 = 0.039 0.26 (6 m i m 0.6 f m2 = 0.028 0.26 (7 where : - stanar eviation of sieve curve. Basing on the above the moifie Mayer-Peter an Müller equation (evelope in Department of Water Engineering Agricultural University of Krakow for beloa transport coul be presente as follows: =[ γ HI f g i Δγ i i 1 3]3 2 Δp i b i (8 (0.25(γ /g where: g i - amount of transporte fraction, H water epth, I slope of water surface, i, specific weight of water, g acceleration owing to gravity, p i - amount of fraction i (in percents, b i with of transporte i-fraction in cross-section. The be stability of mountain rivers increases after forming of armore layer on the be surface. This process may be escribe by two curves: an initial curve for nonheterogeneous material an a final curve for heterogeneous material, in which the stanar eviation of the sieve curve reaches δ =1.3 [Sentürk 1977]. Hyraulic parameters of armore layer forming can be escribe on basis of stochastic nature of be loaovement propose cr by Gessler: q (7 g p 0 where: q g probability of no movement of grains, o sheer stresses, p the function of surplus of sheer stresses. Also mean iameter varies uring formation of an armore layer. When floos pass own rivers with polyfractional non-cohesive beaterial, they first transport the finest soli particles an then the larger stones which initially resist the erosion process. After floo be material may return to the initial structure, which escribes the actual be. The critical shear stresses calculate using Wang [1977] function varies with the change of be stability. The
prognosis of the sieve curve change can be one using ARMOUR software in which the Gessler s equation is implemente. Be armoring causing the change of be roughness influences the water flow resistance [Bartnik et al. 2001]. Be roughness can be escribe using roughness measure K [m] [Strużyński 2001]. The armouring process influences the conitions of flow. Velocity profile in Mountain Rivers epens on change of be roughness, which causes rating curve change [Bartnik, Strużyński 2002, Bartnik et al. 2001]. 3. FORMATION OF GRAVEL BARS During its movement ownstream along the river bottom the beloa tens to prouce seiment structures attache to a riverbe or to its banks. Such structures are commonly recognize as channel bars. River bars, or closely relate features, are typical for all rivers an are mimicke in the other linear shear flows [Church an Jones 1982]. There is no formal criterion which has been evelope yet for occurrence of bars in terms of flow an seiment characteristics. Bars, efine as accumulation of seiment grains, or san an/or gravel eposits [Whittow 1984], cannot evelop if the flow epth is approximately equal to the minimum grain size. Consiering alluvial channel three types of bars coul be commonly recognize: alternating bars, point bars an brai bars [Selby 1985]. Alternating bars form in straight channels segments within curves of meanering thawleg. Point bars evelop in the areas of relatively low stream power at the insie of channel meaner. Brai bars, mostly iamon-shape, are often associate with coarse material. They are aligne to the flow an calle longituinal bars [Selby 1985]. Braiing processes are highly ynamic, with rapi interactions between channel configuration, flow, an seiment transport. As specifie before, braie rivers are associate with high-energy environments, high seiment loas, an unstable channel banks. Although most braie rivers appear to aopt a braie pattern at all stages [Bristow an Best 1993], the platform characteristics of braie channels can change raically with ischarge. The number of bars exposeay vary significantly with flow stage, an complex sequences of erosion an eposition may take place as the stage varies. Bar growth an channel erosion occur more or less simultaneously, anost expose bars are the result of complex multiple erosional an epositional events [Southar et al., 1984]. Although bar forms have been commonly escribe in sany or gravely meanering rivers, little attention has been given to the role of obstructions in controlling geomorphic forms in coarsegraine environments [Carling an Reaer 1981, De Jong an Ergenzinger 1995]. Figure 1. Typical gravel river bars
4. MODELING AS A WAY OF DEALING WITH FLUID DYNAMICS, BEDLOAD TRANSPORT AND SOME HYDRAULICS PARAMETERS RESPONSIBLE FOR FLUVIAL PROCESSES A CASE STUDY EXAMPLE Numerical aplications are useful tools in computation flui ynamics. They can be use, for example, for optimalization purposes when esigning hyraulic structures. Some examples of that applications are ARMOUR an TRANS proceures, HEC-RAS software, FLUENT an CCHE2D or CCHE3D moels. The ARMOUR is a DOS interface software use to etermine be stability for passing floo, gravel aggraations an egraation on basis of Gessler s function, Wang hiing factor an shape of grains. It is eicate to mountain rivers. TRANS software calculates be loa transport. It s calibrations were one in Polish mountain rivers where gravel mean iameter size often overcomes 0.05 m. Be loa transport is calculate using M-P-M equation with Shiels factor epene on hiing factor. Those two proceures are evelope at Department of Water Engineering at the Agricultural University of Cracow base on raiotracer beloa transport methos (Michalik, 1990, Michalik, Bartnik 1994. One of the most famous moels comes from National Center for Computational Hyroscience an Engineering (NCHE, University of Mississippi, USA. This is a CCHE2D moel. CCHE2D is a state-of-the-art two-imensional, unsteay, turbulent river flow, seiment transport moel (Jia, Wang 2001, Wu 2001, Duan et al. 2001. Besies computations of flui ynamics the moel is targete for engineers applications incluing preiction river be an bank erosion, meaner migration an seiment transport. After utilization of the computation flui ynamics applications, one can investigate the forecasting of fluvial processes. The example work was one on the Skawa River within back-water reach of the Świnna Poręba Water Reservoir. The aim of the case stuy carrie in at Department of Water Engineering at the Agricultural University of Cracow was to moel fluvial processes along the Skawa River research reach within the influence of a back-water cause by the maximum water level of the water reservoir Świnna Poręba. Those processes have influence on exploitation of reservoir an safety passage of floos. There are several cities an villages within the back-water of Swinna Poreba reservoir. Deposits can cause change river be an hyraulic parameters, which increase grounwater water level an water level uring floo events. The measurements near Zembrzyce were carrie on in 31 cross-sections along 1800 m. The crosssections are locate on the Skawa River in the Swinna Poreba water reservoir backwater rich between two tributary mouths: the Paleczka an Tarnawka Streams. Cross-section XIV-XIV Fig. 2. Simulate water surface for ischarge Q=35 m 3 s -1 an ifferent reservoir water level
When using the CCHE2D moel a simulations were one for several water ischarges Q=35, 112 an 205 m 3 s -1 an for reservoir water level 304.56, 306.50, 307.80 an 309.60 m a.s.l. Some examples of results are escribe below [Bartnik et al. 2004a, 2004b]. Simulations shows that average slope of water level tens to reach a slope of the whole Skawa River valley - 4.1. In Figure 2 there is calculate a reservoir water surface level for water ischarge Q=35 m 3 s -1. At this flow conitions the back-water region is rather small anoves up an own along a istance about 1.5 km, epening on the water reservoir water level. For any other higher flow rate that istance is longer. As an incipient motion criterion of beloa transport very often shear stress is use. There is a strong influence of reservoir water level in selecte cross-section on incipient of motion of seiment. Critical shear stresses calculate using ARMOUR software along crosssection XIV-XIV for armoure be equal to 70 N m -2. A eposition takes place when o < cr. For normal reservoir water surface at selecte cross-section one can expect strong eposition for ischarge Q=205 an 112 m 3 s -1 (there is no seiment transport for ischarge Q=35 m 3 s -1. For reservoir water surface lower than normal one an Q=112 m 3 s -1 iniviual grains bigger than mean iameter start settling at selecte cross-section when for Q=205 m 3 s -1 formation of armouring layer take place. When the reservoir water level fall to 304.56 or lower the eposition zone move ownstream. The eposition zones appear within back-water reach. Lowering reservoir water surface level for about 5 m isplace eposition zone for about 1.3 km ownstream. For any other higher flow rates an ifferent reservoir WSL this istance will be longer. Beloa transport cause changes of beaterial properties. The meian size 50 for ischarge Q=205 m 3 s -1 increase where erosion take place. This is a result of washing away small fractions of beaterial. This process is visible in increasing of meian size 50 from about 0.06 m to about 0.1 m. Entere to the motion beaterial is transporte an eposite within back-water reach of reservoir. In that case meian size 50 ecrease to about 0.04 m an finally reach the initial one size. A total beloa transport rate for selecte crosssections I, III, IV, X, XIV an XXVI of research reach of the Skawa River for reservoir WSL 304.56 a.s.l. an normal WSL 309.60 m a.s.l. is presente in the Fig. 3a an 3b. The total beloa transport rate is obtaine by summing beloa transport in noes along the selecte cross-sections. The water reservoir surface level has the influence on the reucing of beloa transport so that is way beaterial eposits within back water reach (Fig. 3b. Fig. 3 a, b. Total beloa transport rate within selecte cross-sections of a section of The Skawa River a without backwater effect, b with backwater effect The amount of beloaaterial transporte uring simulate passage of floo was evaluate using TRANS proceure for about 1100 m 3. That baaterial will be gathere in the water reservoir within back-water reach. The accumulateaterial will increase a river be level. The reuction of active cross-section will increase a water surface level uring a floo. It is
necessary to investigate the eposition processes uring exploitation of water reservoir in orer to avoi flooing a nearest village Zembrzyce. 5. RECAPITULATION The paper concentrates on escription of some basic parameters an features of the mountainous stream which are responsible for morphoynamical changes. It eals firstly with: mountain streams incipient motion an beloa transport outlook formation of gravel bars moeling as a way of ealing with flui ynamics, beloa transport an some hyraulics parameters responsible for fluvial processes a case stuy example All the work an experience what the authors presents above were one in water basin of the Skawa River situate in Polish part of the Carpathians Mountains, in the Beskiy Mountains. REFERENCES Bagnol R. A., 1986. Transport of solis by natural water flow: evience for worl-wie correlation, Proceeings of the Royal Society of Lonon, A 405, 369-374 Bartnik W., 1992. Fluvial hyraulic of streams anountain rivers with mobile be. Beginning of be loaotion, Zeszyty Naukowe AR, Cracow, No. 171 Bartnik W., Strużyński A., 2002. Estimation of hyraulic parameters of armore layer forming in mountain rivers an streams, Avances in Hyro-Science an Engineering, ICHE an Warsaw University of Technology, publishe on CD-ROM Bartnik W., Banasik K., Ksiazek L., Raecki-Pawlik A., Struzynski A., 2004a. Hyroynamics balance of the Skawa River within the influence of the back water of the Swinna Poreba water reservoir, 12th International Conference on Transport an Seimentation of Soli Particles, Praha, Czech Republic Bartnik W., Ksiazek L., Michalik A., Raecki-Pawlik A., Struzynski A., 2004b. Moeling of fluvial processes along a reach of the Skawa River using CCHE2D software, 12th International Conference on Transport an Seimentation of Soli Particles, Wroclaw, Polan Bartnik W., Florek J., Książek L., Strużyński A., 2001 Dynamic roughness changes at river with movable be, Zesz. Nauk. AR w Krakowie, ser. Inżynieria Śroowiska, nr 21, 129-138, in polish Bristow C. an Best J. 1993. Braie rivers: perspectives an problems. Geological Society of Lonon, 75, 1-11 Carling P.A., Reaer N.A. 1981. Structure, composition an bulk properties of uplan stream gravels. Earth Surface Proc. an Lanforms, vol.7, p. 349-365 Church M.A., Jones D. 1982. Channel Bars in Gravel-Be Rivers, Gravel-be Rivers, Eite by R.D.Hey, Lonon, p.291-325 De Jong C., Ergenzinger P. 1995. The interaction between mountain valley forms an river be arrangement, Free University of Berlin, in River Geomorphology eite by Hickin E.J., John Wiley an Sons, New-York, p. 54-91 Duan J.G., Wang S.S.Y., Jia Y., 2001. The applications of the enhance CCHE2D moel to stuy the alluvial channel migration processes, J. of Hyr. Research, Vol. 39, 469-491. Einstein H.A., 1950. The be loa function for seiment transportation in open channel flows, Technical Bulletin 1026, U. S. Department of Agriculture Gessler J., 1970. Self stabilising tenency of alluvial channels, Journal of the Waterway, Harbours an Coastal Engineering Division, ASCE, Vol. 96, No.2, 239-249
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