Available online at ScienceDirect. Procedia Engineering 125 (2015 )

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1 Available online at ScienceDirect Procedia Engineering 125 (2015 ) The 5th International Conerence o Euro Asia Civil Engineering Forum (EACEF-5) The presence o Jeringau (Acorus calamus) as lexible vegetation type in the channel against low resistance Maimun Rizalihadi a, *, Dian Saiana a a Civil Engineering Department, Engineering Faculty, Syiah Kuala University,Banda Aceh 23111, Indonesia Abstract Flow resistance in the channel is inluenced not only by material orming the bed and slope o channel, but also inluenced by abstraction due to the presence o vegetation in the channel, so called vegetated channel. The presence o vegetation may greatly aect the conveyance o a channel. The study is aimed to investigate the eect o lexible vegetation density o jeringau (Acorus calamus) to low resistance. The research is conducted in the laboratory by using a channel-lume with dimensions o 15.5 m length, 0.5 m width, and 1.0 m height in which in the central part o 1.4 m length o lume is planted with Jeringau in submerged condition. The vegetation density is set in 6 variations, namely: 0, 6, 12, 18, 30 and 42 plants/m 2. Flow velocity at surace, 0.2h, 0.6h, 0.8h and bed level are measured using micro-current meter to see velocity distribution proile in three parts o upstream, central (vegetating part) and the downstream o channel. At those point are also measured the water depth using point gauge to see the head losses or analyzing Manning s roughness coeicient (n). Based on the measurements and analysis, it is obtained that the presence o Jeringau might change velocity distribution compared to unvegetated channel. The more increase the density o Jeringau, the more increase the head losses which result on increasing Manning s roughness coeicient. The largest n value is 0.053, obtained rom maximum density, and 0,022 or unvegetated channel. The result shows that n value increase 2.41 times due to the presence o Jeringau vegetation. It can be conclude that the presence o vegetation can increase the value o roughness coeicient aecting low resistance, so as to disturb the water low in a channel The Authors. Published by by Elsevier Elsevier Ltd. Ltd. This is an open access article under the CC BY-NC-ND license Peer-review ( under responsibility o organizing committee o The 5th International Conerence o Euro Asia Civil Engineering Forum Peer-review (EACEF-5). under responsibility o organizing committee o The 5th International Conerence o Euro Asia Civil Engineering Forum (EACEF-5) Keywords: Flow Resistance, Vegetated channel, Jeringau (Acorus calamus), Manning s roughness coeicient. * Corresponding author. Tel.: ; ax: address: dilamalia@hotmail.com The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license ( Peer-review under responsibility o organizing committee o The 5th International Conerence o Euro Asia Civil Engineering Forum (EACEF-5) doi: /j.proeng

2 Maimun Rizalihadi and Dian Sai ana / Procedia Engineering 125 ( 2015 ) Introduction Flow resistance in the channel is inluenced not only by material orming on bed and slope o channel but also inluenced by obstruction due to the presence o vegetation in the channel, so called vegetated channel. The presence o vegetation has a major eect on the low resistance. Flow resistance due to vegetation may greatly aect the conveyance o channel, reducing low velocity and consequently increasing head losses o energy and resulting on sediment deposition in the channel bed and banks, [1]. Thus, in order to cope with new management in hydraulics, the inluence o vegetation in the channel becomes important. Nomenclature C Chezy coeicient n w Sidewall Manning s Coeicient D Water depth n v Vegetative Manning s coeicient Darcy-Weisbach coeicient R Hydraulic Radii g Gravity V b Velocity on bed o channel I the slope o energy V d downstream mean velocity H Water depth V 0.2 Velocity on 0.2 o water depth H u Upstream water depth V 0.6 Velocity on 0.6 o water depth H d Downstream water depth V 0.8 Velocity on 0.8 o water depth L lenght o tes area V s Velocity on surace o channel n Manning s coeicient V u Upstream mean velocity h Head losses V Mean velocity n Manning s coeicient Many researchers have already been carried out in order to describe the relationship between low resistance and the presence and spatial distribution o vegetation. They resulted and developed the theories and ormulas dealing with the low resistance due to the presence o vegetation. [2,3] explained low resistance in term o bed material roughness including roughness o vegetation, so called, Manning s coeicient (n). [4 6] have carried out in developing resistance equation or channels with lexible and sti vegetation in condition submerged or partially submerged plants. Also detailed plant characteristics (leas, bending) with various combinations may have an important inluences on low resistance [7 11]. However the prediction o the vegetation resistance is very complex since there are many dierent species with their own uniquee characteristics changing during the season. These plant characteristics are inluencing the hydraulic resistance, which may vary signiicantly rom place to place, and may also change in time. Beside that the inhomogeneous characteristic o the vegetation in the ield that is hard to take into account in model o equation. Another important aspect o describing vegetation is the lexible vegetation [12]. The bending o vegetation decreases the height o the vegetation inluencing the resistance. Moreover, the dierence o type dan characteristic o vegetation might result on dierent low resistance, although these vegetations are equally lexible or sti vegetation. Thereore the evaluation o low resistance or dierent type and characteristic o vegetation is an essential task in open channel hydraulics in order to obtained the most suitable approach or general application. The purpose o this paper is to investigate the determination o the low resistance caused by jeringau (Acorus calamus). The paper presents a practice-oriented procedure or determining Manning s roughness (n). Emphasis is put on inluencing the dierence density o vegetation against low resistance. The research is limited to the case o jeringau (Acorus calamus) as lexibel typical vegetation with submerged condition with single low depths o 45 cm and uniorm jeringau vegetation o cm tall.

3 252 Maimun Rizalihadi and Dian Sai ana / Procedia Engineering 125 ( 2015 ) Theotical considerations The resistance o a surace can be characterized with several hydraulic roughness coeicients. The most widely used are the Manning roughness coeicient (n) as in Eq. 1, the Chezy resistance actor (C) as in Eq. 2, and the Darcy- Weisbach riction actor () as in Eq /3 1/ 2 V R I n (1) V C RI (2) 2 L V h D 2 g (3) Manning s n is most popular in computation o open channel, overland lows and soil erosion models, while using the Darcy-Weisbach is more common than the other resistance ormulations in experimental studies, [9]. Manning s n is most popular in computation o open channel, overland lows and soil erosion models, while using the Darcy- Weisbach is more common than the other resistance ormulations in experimental studies. In [8] is described that many published values o Manning s roughness coeicients related to vegetated suraces include the base resistance, n0, as a part o the reported vegetation resistance. Thus, roughness coeicients reported herein include the eects o both the bed (n o) and the vegetation (n 4), expressed as n o + n Method o research 3.1. Experimental set up Experiments were conducted in a 15.5 m long, 0.5 m wide and 1.0 m deep glass-walled lume. The slope o the lume is set with ixed slope o 0%. Discharge o 5.53 l/s is conducted through one V-notch gate, in which water level o 45 cm can be maintained at a constant level. The soil orming bed lume was layered by ine sand with 15 cm thick to make the same condition as test area. The test area was set in the midle o lume with 3 m long and planted by jeringau (Acorus calamus). Jeringau is This plant has long thin lea o cm tall and cm wide and lexible vegetation due to water low. This plant is planted in the lume with cm tall o jeringau in submerged condition, as depicted in Fig. 1, and is planted with 6 variations o density, namely; 0, 6, 12, 18, 30 and 42 plants/m 2, as shown in the Fig The Series o measurements and analysis Fig. 1. Submerged vegetation layout The series o measurements under ixed discharge o 5.53 l/s is run on the test area with dierent trial test o vegetation density. The series o measurements are completely shown in in the Table 1. The velocity o low was measured using micro currentmeter which was put at upstream1 m beore test area and at downstream 1 m ater test area. The measured was conducted at bottom, 0.2h, 0,6h, 0.8h and surace level to obtaine the poile o velocity distribution, and then by using Eq. 4 the mean velocity can be calculated.

4 Maimun Rizalihadi and Dian Sai ana / Procedia Engineering 125 ( 2015 ) V m Fig. 2. Vegetation density layout Vs 3V 0.2 2V 0.6 3V 0. 8 Vb (4) 10 Table 1. The series o Measurements and Analysis. Series o Vegtation Density Data Measurements (plants/m2) Measurements Analysis VD-0 0 (Hu, Hd, V)00 (h I, n) 00 VD-1 6 (Hu, Hd, V)06 (h I, n) 06 VD-2 12 (Hu, Hd, V)12 (h I, n) 12 VD-3 18 (Hu, Hd, V)18 (h I, n) 18 VD-4 30 (Hu, Hd, V)30 (h I, n) 30 VD-5 42 (Hu, Hd, V)42 (h I, n) 42 Water depth was recorded at the upsteram and downstream o test area with a point gauge. Total head loss o energy was calculated using Bernoulli s equation or elevation Z 1= Z 2 as written in Eq V u V d Hu H d h (5) 2. g 2. g and slope o energy can be obtained using the ollowing equation. h I (6) L In this study, Manning s n is used to denote the low resistance, as stated in [12,13]. The total resistance o the testing lume is a result o the sidewall and bottom resistance, designated as n w and n b, respectively. Since the bed resistance is dominated by the vegetative roughness rather than the surace riction o the bottom, n b may well be used to represent the vegetative roughness coeicient (n v). Meanwhile n w is reprented by n o (The manning s coeicient or unvegetated channel so called boundary riction). So the Manning s coeicient (n) in Eq. 1 is the total boundary riction (n o) and vegetated resistance o low (n v), as written in Eq.7. By this, then the vegetative roughness o Manning s coeicient (n v) can be obtained using Eq. 8. n no n v (7) n v n n o (8) 4. Results and discussions 4.1. The proile o velocity to water depth The velocity were measured at bottom, 0.2h, 0,6h, 0.8h and surace level to obtaine the poile o velocity distribution, the results is shown in the Fig. 3. The igure showed that the proile o velocity with no vegetation give the logarithmic relationship to water depth. But due to the presence o plats, the proile o velocity turns into tow

5 254 Maimun Rizalihadi and Dian Sai ana / Procedia Engineering 125 ( 2015 ) distinc layers, in which signiicantly change in water depth o 0.2 to 0.6h, as in Fig. 3. So the proile o velocity can not it a logarithmic except in the unvegetated layer. The result is quite relevant to [2,3,7,14], they stated that For submerged conditions the vegetation is relatively high in relation to the low depth, as a consequence the velocity proile changes a lot over depth, as shown in Fig. 3. At the bed o the channel, the velocity is inluenced by the bottom roughness. Inside the vegetation rom the bed and the top o the vegetation, the velocity is tending to be uniorm. Near the top o the vegetation there is a transitional proile between the velocity inside the vegetation and the higher velocities above the vegetation. Because o the dierence in velocity in these two layers, descriptions or submerged vegetation are oten based on a two-layer approach. The two-layer approach describes the velocity inside the vegetation layer separately rom the velocity inside the layer above the vegetation, the so called surace layer. Above the vegetation oten a logarithmic proile is assumed or the velocity distribution in the surace layer. This shows that the presence o jeringau can also inluence the proil o velocity Flow resistance against vegetation density Fig. 3 The Proile o Velocity or Variation o Density to Water depth As stated above that the low resistance was denoted by Manning s coeicient (n). Using Eq. 7 the roughness coeicient o Manning on the basis o mean velocity or every density o vegetation can be obtained. Fig. 4(a) is the curve o the Manning s coeicient on the basis o mean velocity against vegetation density. The curve shows that the more dense o vegetation the more increase o Manning s coeicient. This condition is caused by low retardation due to the presence o vegetation, So that the velocity in this layer tend to be decreasing as Fig. 3., aecting on increasing the low resistance which signiicantly relate to increasing on Manning s coeicient. The Manning s coicient is also plotted against the water depth, as shown in Fig. 4(b). The igure reveals that the curves have a consistent pattern o variation compared to Fig.3. With the increase o water depth and vegetation density, the Manning s coeicient or low resistance tend to be increasing to the depth. Fig. 4. (a) The Vegetation Density to Manning s Coeicient; (b) The Water Depth to Manning s Coicient

6 Maimun Rizalihadi and Dian Sai ana / Procedia Engineering 125 ( 2015 ) Table 2. The Total, bed and Vegetated Roughness o Manning s Coeicients. Vegetation Density Manning s Coeicient (plants/m 2 ) Total (n) Bed (n o) Vegetation (n v) The above result shows that Manning s n, representing the total resistance induced by the boundary riction and vegetation. The Manning s coeicient due to vegetation (n v) can be substracted using Eq. 8 and the results can be seen in Table 2. It can be described that the more incresing density o vegetation the more increasing the Manning s coeicient (n v), giving additional roughness in between up to Or in total,the Manning s coeicient due to the presence o jeringau increase in between I compared to unvegetated Manning s coeicient o 0.022, in total the manning s coeicient increase in between 1.5 up to 2.41 times. The results showed that the presence o jeringau (Acorus calamus) can increase the low resistance which is denoted by increasing the manning s coeicient. Thereore, the low resistance o estimation is becoming an essential task o hydraulic engineer in order to avoid not only miscalculation o low variables, such as the water depth, velocity, and shear stress, but also the prediction o their derivative outcomes, such as the time o concentration, low distribution in a basin and the transport o sediment. 5. Conclusions An experimental study has been conducted using jeringau (Acorus calamus) as lexible type o vegetation to investigate the low resistance, Based on the result can be concluded as ollows: 1. The presence o dierent density o jeringau can change the proil o velocity compared to unvegetated channel. 2. The low resistance is converted into the roughness coeicient with the aid o Manning s equation. The presence o jeringau can eect the low resistace, in which the more increase density o jeringau, the more increase the Manning s coeicient (n). Totally the manning s coeicient increase between times. Acknowledgements The writers would like to thank Dian Saiana and Hidrotechnic Laboratory technicians o Civil Engineering Department, Syiah Kuala University, Aceh, or carrying out the lume experiments. Also thank to the Syiah Kuala University or providing me the und to attend this program. The writers appreciate the constructive comments and suggestions provided by EACEF S reviewers and Committee or giving us to attend the Seminar and helping in improving the quality o this article Reerences [1] Yen,B.C. Open Channel Flow Resistance, J. Hydraulic Engineering, 128(1), (2002), pp [2] A.A. Galema, D. C. M. Augustijn, F. Hutho. Vegetation resistance; Evaluation o vegetation resistance descriptors or lood management, Master Thesis, Faculty o Engineering Technology Water Engineering & Management, Twente University, Drienerlolaan, (2009) [3] Augustijn, D.C.M, Hutho, F., & Velzen, van E.H. Comparison o vegetation roughness descriptions, international conerence on luvial hydraulics, (2008).

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