HYDRAULIC COMPARISON OF STANDARD VERTICAL SLOT AND MULTI STRUCTURE SLOT FISH BYPASS

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1 HYDRAULIC COMPARISON OF STANDARD VERTICAL SLOT AND MULTI STRUCTURE SLOT FISH BYPASS M. Tauber 1 and H. Mader 2 1 Department of Water Atmosphere Environment, Institute for Water Management, Hydrology and Hydraulic Engineering, WAU IWHW University of Applied Life Sciences, Muthgasse 18, A-119 Vienna, Austria. michael.tauber@boku.ac.at Phone: Department of Water Atmosphere Environment, Institute for Water Management, Hydrology and Hydraulic Engineering, WAU IWHW University of Applied Life Sciences, Muthgasse 18, A-119 Vienna, Austria. helmut.mader@boku.ac.at Phone: ABSTRACT As many optimisation inquiries in the past just examined ecological optimisations of Vertical Slot Fishpasses, the present research project also focuses on the economical optimisation to meet the contrary demands between the EU-wide aim of river continuum restoration at migration barriers (Water Framwork Directive - 2/6/EG) and the aim of enhancing energy production from renewable energy sources (Renewable Energies Directive - 21/77/EC). The result of various biologic and hydraulic investigations at 1:5 and 1:1 hydraulic models is a modified type of the Vertical Slot Fishpass which uses intended losses at roughness obstacles by obtaining isolated roughness flow in between them. Lower flow velocities and reduced turbulences enhance fish passage capability effectively as trials with fish showed. Hydraulic investigations within a 1:1 hydraulic model with 25 tested different variants yield in a significant reduction of flow velocities and turbulances. In comparison to a standard Vertical Slot Bypass the optimised Multi-Structure Slot principle of the MABA Fishpass shows a clear reduction of flow velocities in the slots, a significant reduction of turbulances, distinct reduction of the energy dissipation rate in the resting pools and therefore a clear enhancement of fish passage capability. As water consumption reduction of the MABA Fishpass was > 34 %, more water can be used at run-off river hydropower sites directly or for operating a residual flow turbine at diversion sites. In comparison to the Standard Vertical Slot Bypasses the follow up costs are reduced considerably, which makes the MABA Fishpass an extraordinarily economical solution. INTRODUCTION The implemantion of the aspired goals were reached by making use of the roughness behaviour of additonal structure elements in the slot areas of the fishway to induce an isolated roughness flow state between them. Further losses will occur due to contraction- and extension effects and the meandering stream course in the resting pool (Tauber & Mader, 29). This paper focuses on the hydraulic comparison of three variants, the standard Vertical slot (V18), the newly developed Multi-Structure Slot Fishpass (V17) and a further optimized variant of it (V25). All were tested with similar specifications (slope 7.5 %, slot width 15 cm). All hydraulic investigations were undertaken at the hydraulic laboratory of the University of Applied Life Sciences, Vienna. Within the first phase, the general feasibility of the idea was clarified with five variants in a 1:5 hydraulic model (Tauber & Mader, 29). Phase two covered an experimental adaptive variant study where different geometrical alignments were tested in an 1:1 hydraulic model in order to reach a maximum between ecological an economical advantages (16 variants). The preferred variant was analyzed in detail for hydraulic design parameter analysis (phase 3). Therefore, 3D velocity and water elevation measurements as well as consumption behavior tests with different slot widths and slopes were undertaken (9 variants). The 1:1 hydraulic model consists of four pools, five slots, an inflow- and an outflow area, all covered with 1 cm of gravel bed substrate. Measurements were taken in the 3 rd and 4 th slot and the 3 rd pool in a grid of 1 x 1 cm in three layers parallel to the fishpass bed with grid refinements in the slot areas. The pool width is set to 1.45 m, the pool length to 2. m, slot width to 15 cm, minimum water depth to bed substrate upper surface of 55 cm and the water level difference from pool to pool to 15.75cm (slope = 7.5 %) for all three described variants.

2 Figure 1: 1:1 Model in the hydraulic laboratory Flow direction Pool 4 Pool 3 Pool 2 Pool 1 Reference Area Measuring Area Figure 2: Model arrangement 3D velocity measurements were taken with an Acoustic Doppler Velocimeter (Nortek ADV) for 3 seconds with a sampling rate of 25 Hz to allow turbulence analysis. Water elevations were measured with an Ultrasonic Distancer (Pepperl + Fuchs, UC5), discharge was measured with a Magnetic Inductive Flowmeter (Endress & Hauser, Promag 5/53W). An automatic positioning measuring bridge allowed the measurement of over 4 measuring points per layer in an appriciable timeframe. To obtain comparable results, only data of the reference area of Figure 2 is taken into account. It contains one pool and one slot area and is accordingly a good representative of one pool section. Measured velocity data in each measuring point was cleaned out of outliers by the criterion 3 < < +3 Where is the arithmetic mean and the standard deviation of the uncleaned data set. This method removes ~ 1.5 % of the data. Accordingly, it can be assumed that the velocity measurement data is a normal distributed variable and the arithmetic mean is an unbiased estimator for the mean velocity. The turbulent kinetic energy, (abbreviated by turbulence in this paper) was calculated according to: e 1 = 2 ( u'² + v'² '²) KIN, t + w Where,, are the mean variant of the flow velocity or the kinetic fluctuation energy in the three coordinate directions. For frequency distribution analysis, the relevant measuring points were gridded with Golden Software Surfer 9 with the gridding method triangulation with linear interpolation in order to avoid measuring value overestimations by other gridding methods (krigging). After blanking out areas of no interest (walls, baffles), areas of similar velocities and turbulences were calculated with the Surfer integrated routine contarea2.bas in order to receive frequency distributions. THE COMPARED VARIANTS Variant 17: The new Multi-Structure Slot principle: Variant 17 is the result of the adaptive variant study among 21 alternatives. It consists of one large resting pool and one stretched slot arrangement with two orifices and a 45 guidance wall at the upstream corner to the pool. Both slots obtain a maximum of roughness at the given scale by obtaining an isolated roughness flow current in between them. Air insertion and turbulences around the pool edge are reduced considerably by the guidance wall.

3 Figure 3: Shematic drawing of the Multi-Structure Slot principle Variant 18: The standard Vertical Slot principle The comparison variant according to the DWVK guideline design criteria. Variant 25: Further improvements to the Multi-Structure Slot principle During investigations on other slopes of the new fishway, it showed that a shorter guidance wall improves flow patterns in the larger pool. Energy dissipation is distributed more equally; maximum flow velocities further decrease and discharge is reduced further by 1 %. RESULTS Consumption For discharge / depth relations a 5 cm thick layer in the bed substrate is taken into account for interflow interactions. Linear regression trials showed that the implementation of this layer obtains an exact hit of the ordinate at the zero point with an error of max +/- 3 %. Thus the minimum depth reference value in Figure 4 is 6 cm. The consumption of V25 (8 l/s) is 44 % lower than of V18 (142 l/s). The guidance wall length reduction in V25 reduces the discharge of V17 (89 l/s) by about 1 %. Minimum water depth in mm 1 MSS s=15, dh=15 (short guidance wall) MSS s=15, dh=15 (long guidance wall) 9 VS s=15, dh=15 8 Linear (MSS s=15, dh=15 (long guidance wall)) Linear (MSS s=15, dh=15 (short guidance wall)) 7 Polynomisch (VS s=15, dh=15) Discharge in l/s Figure 4: Comparison of discharges Flow pattern and velocities For fish migration, the corridor between the fishway bed and 1/3 of the water depth is of interest. Accordingly Figure 5 just shows results of measuring layer three, which is 15 cm above the bed substrate upper edge. Layer one is close to the water surface and layer two is in distance of 15 cm in between the others. V18 in its current design has two different flow states. One with a shortcut flow between the slots along a bigger water cushion in the pool and one with a diagonal flow directly into the opposite pool edge with two recirculation eddies bilateral of it as it is shown in Pena & Teijeiro et al. (23). For these model trials, the former one was the more stable state and was accordingly chosen for comparison. In consumption behavior is a small difference of approx. +8 l/s for the shortcut flow state than for the other.

4 Mean Flow velocity in cm/s V18 (Vertical Slot) V17 (Multi-Structure-Slot) V25 (modified V17) Figure 5:: Flow velocity patterns in measuring layer 3 (close to fishway bed) The maximum velocity measured in V18 was 194 cm/s, in V cm/s and finally in V cm/s which is a reduction of about 27 % from V18 to V25. The area weighted mean flow velocity in measuring layer three is 38 cm/s for V25, 39 cm/s for V17 and 48 cm/s for V18 (26 % higher than in V25). In all three variants velocities between 2 and 5 cm/s are the most frequent. Considerably different is the distribution beyond values of 9 cm/s. Here V18, the Vertical Slot variant, has a share of 9 % while V17 (3 %) and V25 (1.5 %) lie far below this value. V17 (35 %) has a little more velocity shares < 3 cm/s than V25 (32 %). V18-E3 35% V17-E3 V25-E3 25% 2% 15% 1% 5% Figure 6:: Frequency distribution of flow velocities in the reference area > Flow velocity in cm/s % -1 Percentage of area 3%

5 Turbulence and energy density Turbulence effects can be mainly found at the sharp edges of the slot baffles, where the approaching flow direction also plays a role. As well as for the velocities the new principle shows clear advantages in comparison to V18. The turbulence level which is exceeded in 5 % (5% fractile) of all cases in the reference area for all layers is 1.79 cm²/s² for V18, 74 cm²/s² for V17 and 77 cm²/s² for V25. The area weighted mean turbulence level in measuring layer three amounts 343 cm²/s² in V25, 296 cm²/s² in V17 and 424 cm²/s² in V18. In general, V25 shows a higher mean turbulence level than the unmodified variant V17 (identifiable on the area of the 3 cm²/s² isoline in Figure 7 and the turbulence frequency distribution in Figure 8). The advantages of the Multi- Structure Slot principle against the Standard Vertical Slot remain undisputed. Turbulent kinetic energy in cm²/s² 3 V18 (Vertical Slot) V17 (Multi-Structure-Slot) V25 (modified V17) Figure 7: Turbulent kinetic energy in measuring layer 3 As well as for the velocity distribution, the turbulence distribution for V18 shows a higher share of higher turbulence levels above 7 cm²/s² (17 %) than V17 (4 %) and V25 (5 %). Low turbulence classes < 3 cm²/s² have their highest shares in V17 (59 %), followed by V18 (54 %) and V25 (46 %). 4% V18-E3 V17-E3 V25-E3 35% Percentage of area 3% 25% 2% 15% 1% 5% % Turbulent kinetic energy in cm²/s² >2 Figure 8: Frequency distribution of turbulences in the reference area

6 The energy density, calculated by the formula given in the DWVK guideline (DVWK, 1996), in the new Multi- Structure Slot Fishpass has lower values of ~ 98 W/m³ for V17 and ~ 66 W/m³ for V25 than the Standard Vertical Slot principle with a value of ~ 114 W/m³ - a clear reduction of 42 % which is caused by the lower discharge. Directly measured mean turbulences levels for the variants restrain a bit different and unproprtional as Figure 9 shows. It confirms that the DVWK s formula is just a rough estimation and does not take care of real local energy dissipation effects. Mean turbulent kinetic energy per layer in cm²/s² V18-E1 V18-E2 V18-E3 V17-E1 V17-E2 V17-E3 V25-E1 V25-E2 V25-E3 Variant / Layer Mean turbulent kinetic energy per variant in cm²/s² Figure 9: Comparison of mean turbulent kinetic energy for all variants and measuring layers as well as the energy density according to DVWK specifications V18 V17 V25 Variant Energy density in W/m³ V18 V17 V25 Variant CONCLUSIONS A hydraulic model, scale 1:1, was built to investigate the possibilities of further optimizations of discharge, velocity and turbulence reductions. The results of the compared trials show, that the newly developed Multi-Structure Slot variants have clear advantages compared with the conventional Vertical Slot construction principle. The implemented stretched slot construction and the guidance wall redirects the water into the outlet jet of the above slot and leads to a better stepwise degradation and energy dissipation of the water level difference from pool to pool. Thus, the elevation difference is degraded in three steps: at the first slot, at the second slot and in the pool through flow recirculation effects. It was possible to reduce the discharge by up to 44% while still maintaining the same water level elevations in the pools as in the Standard Vertical Slot variant. Concurrently the maximum flow velocities were also reduced by 27 % and the mean turbulent kinetic energy by 19 %, thus achieving the primary goal of this research project of enhancing fish passage capability and reducing the necessary discharge. In special, the two compared variants of the Multi-Structure Slot Fishpass with either a short or a long guidance wall have contrary advantages. While the variant with the long guidance wall offers the lowest mean turbulence level, the other with the short guidance wall comes with the lowest maximum flow velocity and a, by 1 % lower discharge. The longer guidance wall variant is able to serve with a higher distribution percentage of low level flow velocities and turbulences. Within the variant with the short guidance wall, the flow pattern in the pool seems to be shaped out more complete because the meandering stream is formed out clearer. LITERATURE DVWK (1996). Fischaufstiegsanlagen - Bemessung, Gestaltung, Funktionskontrolle (Heft 232/1996), Deutscher Verband für Wasserwirtschaft und Kulturbau e. V. (DVWK). EuropeanParliament and Council (2). Directive 2/6/EC establishing a framework for Community action in the field of water policy. E. Union. 2/6/EC: 72. EuropeanParliament and Council (21). Directive 21/77/EC on the promotion of electricity produced from renewable energy sources in the international electricity market. E. Union. 21/77/EC: 8. Tauber, M. and H. Mader (29). Development of an Economical and Ecological Optimized Multi Slot Fish Bypass. Small Hydro 28. Vacouver, Canada.