Experimental Study on Velocity Profiles Due to Ecological Barriers

Robby Yussac Tallar

and Teofilus Sawang

Civil Engineering Department, Maranatha Christian University, Jl. Surya Sumantri 65, Bandung, Jawa Barat, Indonesia

Keywords: Ecological Barriers, Experimental Study, Velocity Profiles.

Abstract: Streams are very complex system. In stream restoration projects, the existence of ecological structures

should be considered as an important variable in the project. A lot of previous research focused on

ecological aspects only, therefore the main purpose of this paper is to examine the velocity profile due to

ecological barriers in downstream area of weir. A laboratory study to investigate the effect of ecological

barriers in terms of velocity profile in 8 m length x 40 cm width a rectangular channel is presented. The

study consists of an extensive set of rectangular flume experiments for flows with certain The results show

that the average velocity (v=0.35 m/sec) was occurred for without ecological barriers condition. By

comparing the scenarios, this study showed that ecological barriers (dl = 25 cm) has the highest velocity (v

= 0.41m/s), meanwhile scenario 5 (v=0.36 m/s) has the nearest velocity with the scenario 1 (v=0.35 m/s). It

indicated that the existence of ecological barriers had given the higher velocities in streams. The distance

length between ecological barriers showed that the farther the distance length used the lower the formed

velocity profiles.

https://orcid.org/0000-0001-7307-3348

https://orcid.org/0000-0002-9861-8831

INTRODUCTION

Streams are a very complex system (Stanford,

Zavaleta, & Millard-Ball, 2018). Not only are the

hydraulic properties complex, but so are the

implications of those properties. Many experts such

as stream engineers, geomorphologists, civil

engineers and ecologists may share a similar

opinion, especially when identifying the variable and

complex stream that includes ecological aspects, can

take place over time and across stream areas

(Magilligan, Nislow, Kynard, & Hackman, 2016;

Rinaldi, Gurnell, Del Tánago, Bussettini, &

Hendriks, 2016; Tallar & Suen, 2015). In stream

restoration projects, the presence of ecological

structures should be seen as an important variable in

the project. Much earlier research has focused on

environmental issues (Chang, 2008; Rosgen &

Silvey, 1996; Tallar & Suen, 2017). Therefore, the

main aim of this paper is to study the velocity profile

due to ecological barriers in the area downstream of

the stream.

The scopes of this study consisted of the research

was conducted in open channel with steady

condition; the sediment used was classified as poorly

graded sand; the type and diameter of the material

are gravel with a diameter of 2cm and covered with

wire mesh; and permeability is neglected because

the sediment/soil condition is already saturated. The

contribution of this study is to describe the existence

of ecological structures should be considered as an

important variable in the stream restoration projects.

METHODS

A laboratory study is presented to investigate the

effect of ecological barriers on the velocity profile in

a rectangular channel 8 m long x 40 cm wide. The

study consists of an extensive series of experiments

with rectangular channels for currents with a certain

slope and a gravel bed.

The design of the ecological barriers can be seen

in Figure 1. The distance length (dl) of each

ecological barrier was set at 25 cm. 50 cm; 75 cm;

and 100 cm. The study used the BACI (Before After

Impact Control) method for established scenarios

(Table 1).

Tallar, R. and Sawang, T.

Experimental Study on Velocity Proﬁles Due to Ecological Barriers.

DOI: 10.5220/0010747400003113

In Proceedings of the 1st International Conference on Emerging Issues in Technology, Engineering and Science (ICE-TES 2021), pages 167-171

ISBN: 978-989-758-601-9

167

Figure 1: Design of ecological barriers.

In this study, Q = 0.02 m3 / s was used when the

constant discharge flows into the channel. Different

scenarios were also run with different limitations.

The limitations of the study consisted of the flowing

discharge and the slope of channel.

Table 1: Scenarios of the study.

Scenario Description

1 Without ecological barriers

2 Ecological barriers (d

= 25 cm)

3 Ecological barriers (d

= 50 cm)

4 Ecological barriers (d

= 75 cm)

5 Ecological barriers (d

= 100 cm)

2.1 Method for Sieve Analysis

The sieve analysis is carried out by set up the

weighed aggregate into a set of pre-arranged sieves.

Particle size determinations on large samples of

sediments are necessary to ensure that sediments

perform as intended for their specified use. A sieve

analysis or gradation test determines the distribution

of sediment particles by size within a given sample.

This information can then be used to determine

study requirements. Data can also be used to

understand the characteristics and classification of

sediment. This study used cumulative method. As

each retained fraction is added, divide the

cumulative mass by the total mass of the sample and

multiply by 100 to calculate percent retained.

Subtract the cumulative percent retained on a given

sieve from 100 to calculate percent passing.

2.2 Method for Flow Velocity Analysis

Flow velocity is simply the continual movement of

water in channels each open and closed. This flow

velocity is constricted connected with discharge,

which defined as the rate of flow or the volume of

water that passes through a channel cross section in

a specific period of time. Discharge can be reported

as total volume or as a rate such as cubic feet per

second (ft

/s or cfs) or cubic meters per second

/s). The terms flow velocity and discharge are

often used interchangeably, but they will be used

only as defined here.

Discharge data are very important to estimate the

characteristics of channel such as rivers or streams.

The aim of drawing the discharge rating curve is to

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168

work out the most discharge from a channel and to get

an outlined discharge in experimental study. A rating

curve may be a graph of discharge versus stage for a

given purpose on a stream or open channel.

RESULTS AND DISCUSSION

3.1 Sieve Analysis Results

The sieve analysis has been performed to determine

the grain size curve distribution of the sediment then

to obtain the uniformity coefficient (Cu) and

gradient coefficient (Cc). The first process of sieve

analysis is set up the weighed aggregate into a set of

sieve numbers inserted into the vibrating device for

10 minutes. Initial aggregate weight is 1000gr. The

results of sieve analysis can be seen on Table 2 and

Figure 2.

Table 2: Sieve analysis results.

Sieve

Number

d (mm)

Soil Retained

(%)

Cumulative

Soil

Retained

(%)

Soil

Passing

(%)

#4 4.75 7.1 7.1 92.9

#10 2.00 17.7 24.8 75.2

#20 0.85 24.2 49.0 51.0

#50 0.30 22.6 71.6 28.4

#100 0.15 20.3 91.9 8.1

#200 0.075 7.1 99.0 1.0

Pan - 0.5 99.5 0.0

The retained percentage and D

, D

has

been

used for sediment classification. From the

graph, it shows that the relationship between grain

size and percent finer so that Cu= 6.94 and

Cc=0.484. By using Soil Classification Chart, it is

classified that sediment is categorized in Poorly

Graded Sand.

3.2 Flow Velocity Analysis Results

The completed analysis of flow rate velocity is taken

by several positions both x and y direction. Several

positions were in cross section area with the width

distance between ecological barriers. The average

flow velocity was measured by taking 3 depth

positions which represented upper, middle, and

lower area. Time duration for each point was 30

seconds. The results can be seen on Figure 3 and

Table 3.

Table 3: Average flow velocity analysis results.

Scenario

Colour line

Average flow

velocity (m/s)

Green 0.35

Purple 0.41

Red 0.39

Yellow 0.38

5 Blue 0.36

Figure 2: Sieve analysis results.

Experimental Study on Velocity Proﬁles Due to Ecological Barriers

169

Figure 3: Velocity profiles for five scenarios (Note: Colours describe scenario 1-5).

3.3 Discussion

Basically, ecological barriers provide the necessary

environmental conditions for aquatic organisms

related to the flow velocity. The spatial and temporal

condition determine the boundary of targeted area

study. In context of velocity profile, the flow

velocity is highest near the water surface an lowest

near the channel bed. The drag forces exerted on

water near the watercourse bed usually account for

the decrease in flow velocity.

According to sieve analysis results, the used

sediment was classified by poorly graded sand. It

can be assumed that the roughness of sediment is

higher than well graded sand. Meanwhile, flow

velocity profiles outcomes are strongly associated

with the roughness of sediment. On a stable channel,

the final result of velocity will be faster but in a

channel with ecological barriers, it can cause a

decrease in flow velocity. The highest flow velocity

is in channel with ecological barriers condition with

distance length 25 cm (scenario 2) and the lowest

velocity is in the channel without ecological barriers

(scenario 1).

The influence of flow velocity profile is also

influenced by other factors such as the placement

and position of ecological barriers in a channel and

the distance between ecological barriers. Different

flow rates also will affect the flow velocity profiles.

The other related parameters considered in this study

are Froude and Reynold Number.

Froude number is the ratio of flow velocity to the

characteristic velocity of water waves in the channel,

whilst the Reynold Number deals with the

relationship between frictional and inertial force.

The higher the velocity, the higher the Reynold

Number. It can be assumed that the existence of

ecological barriers can increase the Reynold

Number.

CONCLUSIONS

The results show that the average velocity (v=0.35

m/sec) was occurred for without ecological barriers

condition. By comparing the scenarios, this study

showed that ecological barriers (dl = 25 cm) has the

highest velocity (v = 0.41m/s), meanwhile scenario 5

(v=0.36 m/s) has the nearest velocity with the

scenario 1 (v=0.35 m/s). It indicated that the

existence of ecological barriers had given the higher

velocities in streams. The distance length between

ecological barriers showed that the farther the

distance length used the lower the formed velocity

profiles. A conceptual framework for

implementation of ecological barriers requires an

understanding of three major aspects

(geomorphology, hydraulics, and ecology).

Moreover, it is necessary to investigate the effect of

other variables such as ecological barriers

dimension, variation of structure models and other

related variables in the further research.

ACKNOWLEDGEMENTS

The authors gratefully acknowledge the support

for this research provided by Civil Engineering

Department, Maranatha Christian University,

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170

Indonesia, and under collaboration research with

Hydraulics and Ocean Engineering Department,

National Cheng Kung University, Taiwan R.O.C.

REFERENCES

Chang, H. H. (2008). River morphology and river channel

changes. Transactions of Tianjin University, 14(4),

254–262.

Magilligan, F. J., Nislow, K. H., Kynard, B. E., &

Hackman, A. M. (2016). Immediate changes in stream

channel geomorphology, aquatic habitat, and fish

assemblages following dam removal in a small upland

catchment. Geomorphology, 252, 158–170.

Rinaldi, M., Gurnell, A. M., Del Tánago, M. G.,

Bussettini, M., & Hendriks, D. (2016). Classification

of river morphology and hydrology to support

management and restoration. Aquatic Sciences, 78(1),

17–33.

Rosgen, D. L., & Silvey, H. L. (1996). Applied river

morphology (Vol. 1481). Wildland Hydrology Pagosa

Springs, CO.

Stanford, B., Zavaleta, E., & Millard-Ball, A. (2018).

Where and why does restoration happen? Ecological

and sociopolitical influences on stream restoration in

coastal California. Biological Conservation, 221, 219–

227.

Tallar, R. Y., & Suen, J.-P. (2015). Identification of

waterbody status in Indonesia by using predictive

index assessment tool. International Soil and Water

Conservation Research, 3(3), 224–238.

https://doi.org/10.1016/j.iswcr.2015.06.009

Tallar, R. Y., & Suen, J.-P. (2017). Measuring the

aesthetic value of multifunctional lakes using an

enhanced visual quality method. Water, 9(4), 233.

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