evaluation of ecohydraulic effectiveness of an artificial fish nest in an agricultural drainage...

E-proceedings of the 36th IAHR World Congress 28 June – 3 July, 2015, The Hague, the Netherlands

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EVALUATION OF ECOHYDRAULIC EFFECTIVENESS OF AN ARTIFICIAL FISH NEST IN AN AGRICULTURAL DRAINAGE CANAL

SHIGEYA MAEDA(1), HIBIKI TANIGAWA(2) , KOSHI YOSHIDA(3) & HISAO KURODA(4)

(1) College of Agriculture, Ibaraki University, Ibaraki, Japan, [email protected]




ABSTRACT

Effectiveness of an artificial fish nest installed on the sidewall of an agricultural drainage canal made by concrete is evaluated by observing the instantaneous current velocity and the water depth at various points in the canal. Using the obtained data, the turbulent kinetic energy, the degree of turbulence, and the energy expenditure (i.e., swimming cost) by fish in the turbulent flow are estimated at 15 monitoring spots. These spots are categorized into two groups: spots in and around the fish nest are in ‘Group 1’, and spots away from the fish nest are in ‘Group 2’. The energy expenditure by fish in Group 1 is estimated as significantly small, which indicates the fish nests contribute to create a preferable fish habitat in the canal.

Keywords: Fish nest, Habitat, Canal, Turbulence, Agriculture

1. INTRODUCTION

An agricultural drainage canal is used for draining paddy fields and upland crop fields around it, as well as for flood control. However, pursuing the effectiveness of these functions sometimes results in destroying fish habitat that the agricultural system intrinsically owns in Japan. Therefore nowadays conservation of fish habitat in a drainage canal is considered important in agricultural engineering. The fish habitat in a river or a canal has been evaluated using various methods such as IFIM (Instream Flow Incremental Methodology), HEP (Habitat Evaluation Procedure) and HSI (Habitat Suitability Index), etc. (Tharme, 2003; Yi et al., 2010). In the evaluation, the time-averaged current velocity is often employed as one of environmental factors of fish habitat in the water body of a canal. Preference of a target fish in the canal with respect to the velocity is evaluated with a value ranging from 0 to 1. However, actually, fish in the canal are influenced by not the time-averaged but the instantaneous current velocity. The effect of turbulent flow on the fish behavior is not taken into account in the conventional fish habitat evaluation.

Fewer researches have been conducted for the influence of turbulence on fish behavior. Pavlov et al. (2000) revealed that alternations in the turbulence intensity of flow cause significant changes in fish rheoreaction: in the threshold, cruise and maximum swimming speed, as well as in their swimming capacity. It has been well documented that turbulence increases the cost of fish locomotion (Silva et al, 2012). Pavlov et al. (2000), Enders et al. (2005), Lupandin (2005), Santos et al. (2012), and Silva et al. (2012) have basically studied the turbulence effect in the experimental channel and fishway. However, researches on the effect of flow turbulence on fish habitat in actual canals seem insufficient, although artificial fish nests have been introduced to canals for restoration of fish habitat in the water bodies in Japan. In this study, therefore, the effectiveness of an artificial fish nest installed in a drainage canal is evaluated by turbulence characteristics and the estimated fish energy expenditure in the stream.

2. QUANTIFICATION OF TURBULENCE AND FISH ENERGY EXPENDITURE

Flow in an agricultural drainage canal is typically turbulent flow, namely, the instantaneous water velocity there fluctuates. If

the instantaneous current velocity is recorded repeatedly, the i-th current velocity component ( )1,2, ,i N= ⋯ in the

Cartesian coordinate, , ,i i iu v wɶ ɶ ɶ , in space can be expressed as

, ,i i i i i iu U u v V v w W w= + = + = +ɶ ɶ ɶ [1]

1 1 1

1 1 1, ,

N N N

i i ii i i

U u V v W wN N N= = =

= = =∑ ∑ ∑ɶ ɶ ɶ [2]

E-proceedings of the 36th IAHR World Congress, 28 June – 3 July, 2015, The Hague, the Netherlands

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where , ,U V W = x, y, z components of time-averaged current velocity vector, respectively; , ,i i iu v w = fluctuating x, y, z

components of turbulent velocity vector, respectively; and N = number of recorded samples on instantaneous current velocity. Then turbulent kinetic energy (TKE) (Silva et al, 2012) is computed by

( )2 2 21TKE

2u v w= + + [3]

where the over bar in Eq. [3] denotes time-average of the related variable, i.e.,

2 2 2 2 2 2

1 1 1

1 1 1, ,

N N N

i i ii i i

u u v v w wN N N= = =

= = =∑ ∑ ∑ [4]

Degree of turbulence, or turbulent intensity (Pavlov et al., 2000), is the important measure of turbulent flow in analyzing fish rheoreaction and necessary to estimate fish energy expenditure as explained below. The x, y, z components of pulsation standard vector, , ,x y zσ σ σ , are defined as

2 2 2, ,x y zu v wσ σ σ= = = [5]

Then, the degree of turbulence, K , can be written as

2 2 2

2 2 20 0

2TKEx y zK

V VU V W

σ σ σσ + += = =

+ + [6]

where σ = magnitude of pulsation standard vector; 0V = magnitude of time-averaged current velocity. It is noted that the

degree of turbulence is the ratio of pulsation standard to time-averaged current velocity, and therefore useful in comparing spatial difference in magnitude of turbulence among the observation points.

The energy spent by a fish to overcome the water resistance in the turbulent flow in the canal can be mathematically expressed as (Pavlov et al., 2000)

320 (1 3 )

2

C SV TW K

ρ= + [7]

where C = coefficient of drag force; ρ = water density; S = projected area of the target fish to the time-averaged flow direction; and T = time. The energy expenditure, W , at a point can be used as a measure for evaluating the value of the point as a fish habitat, because it is certain that the less energy expenditure (swimming cost) is, the more desirable it is for the fish. It is noteworthy that degree of turbulence, K , is necessary for quantifying the energy loss of a fish as well as the time-averaged water velocity, 0V .

3. METHODS

3.1 Study area

The study area is a pair of sections of agricultural drainage canal located in Ibaraki Prefecture, Japan (Figure 1). The canal conveys water issuing from paddy fields surrounding the canal to the Takahashi River which is one of the influent rivers of Lake Kasumigaura. It is reported that fishes such as Rhinogobius, Zacco platypus, Misgurnus anguillicaudatus, Plecoglossus altivelis, Mugil cephalus, Gymnogobius urotaenia swim upstream from the lake in the river and the canal. In the downstream canal section, named ‘Section 1’, six artificial fish nests were installed on the sidewall of the canal made by concrete in 2002 (Figure 2). Section 1 is 3.9km upstream of the mouth of the Takahashi River. The authors caught fishes of Misgurnus anguillicaudatus, Gnathopogon elongatus, Tridentiger brevispinis, Rhinogobius sp. DA in the section in 2013 and 2014. In contrast to Section 1, a canal section without artificial fish nests is selected, which is called ‘Section 2’ and located about 100m upstream of Section 1. These two canal sections have rectangular cross-sections, and the bed and sidewalls are made by concrete. Large amount of solid is depositing in the lying pipes connecting the neighboring two fish nests (Figure 2).

Figure 3 shows the A-A’ cross section of the canal, which has two fish nests, in Section1. Mud sediments on the canal bed within the fish nests because of rapid decrease of current velocity caused by the expansion of cross-sectional area in Section 1. The bed of the main canal consists of artificially scattered gravel and sediment on them. In contrast, there exist little sediment on the canal bed made of concrete in Section 2.

3.2 Field observations of hydraulic status

Hydraulic observations were carried out three times on (1) 10 October 2013 (Observation 1), (2) 24 April 2014 (Observation 2), and (3) 16 June 2014 (Observation 3). These were all sunny days. Since the canal sections are surrounded by paddy fields, the stream is affected by agricultural practices in the fields. Observation 1 was after rice harvesting and within the non-irrigation period. On the second observation day, paddling water used in the surrounding paddy fields were discharged to the canal. Thus turbid water flew in the canal sections. The third observation day corresponds to the date about one month after rice transplanting.


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As shown in Figure 2, twelve and three monitoring spots S1-S12 and S13-S15 are set in Sections 1 and 2, respectively for observing instantaneous current velocity and water depth for three days. The three-dimensional current velocity components were recorded at a frequency of 80Hz for a sampling period of 25 seconds (Observation 1) and 30 seconds (Observations 2 and 3) at each monitoring point by electromagnetic current meter VP3500 (Kenek).

Current velocity changes vertically even in the same monitoring spot. For Observation 1, only one point at each monitoring spot is chosen to observe the instantaneous current velocity, namely, 0.1m and 0.05m above the canal bed at S1-S12 and S13-S15, respectively. Regarding Observations 2 and 3, the vertical locations of monitoring points depend on the local water depth at the spots. At S4-S12, points of 20% (i.e., near the canal bed) and 80% (i.e., near the water surface) of the water depth are chosen for observing current velocity, whereas at S1-S3 in the fish nest, points of 20% of the water depth are used because of instrumental constraint. Since water depth in Sections 2 is shallow, points of 40% of the water depth are selected for the measurements. The recorded data at these points are used to compute the time-averaged velocities, the turbulent kinetic energy, the degree of turbulence and the energy expenditure.

Figure 1. Study area.

Figure 2. Plane view of Sections 1 and 2 and monitoring spots in the agricultural drainage canal.


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Figure 3. Transversal cross section of the canal (A-A’ in Figure 2) with two fish nests in Section 1.

4. RESULTS AND DISCUSSION

Fifteen monitoring spots given in Figure 2 are categorized into two groups. Nine spots, S1-S9, positioned ‘in and around the fish nest’ are in ‘Group 1’. Remained six spots, S10-S15, arranged ‘away from the fish nest’ in the drainage canal are in ‘Group 2’. The ecohydraulic effectiveness of the fish nest is investigated by comparing the estimated fish energy expenditure considering the degree of turbulence in Groups 1 and 2.

Figure 4 shows the x, y, z components of instantaneous current velocity collected at the point of 80% of the water depth at S11 on 24 April 2014. The ranges of observed water depth and current velocity are listed in Table 1. Values of water density in Eq. [7] are 997.6, 998.9 and 997.7kg/m3 since water temperature in Observations 1, 2 and 3 are 22.7, 16.3 and 22.4℃, respectively. The coefficient of drag force is assumed 0.01 based on Pavlov et al. (2000). Since we captured fish of Tridentiger brevispinis whose total length is 0.063m and body height is 0.01m in Section 1 on 22 May 2014, the fish species is determined as the target one. The projected area S in Eq. [7] is thus set as 7.85 ×10-5m2. The computed TKE, K and W using Eqs. [3], [6] and [7] are also summarized in Table 1.

TKE takes the minimum values at S1, S5 and S6 locating within the fish nest, while the maximum at S11 and S12 which are far from the fish nest. K takes the maximum at S1, S2 and S9 that are in and around the fish nest, whereas the minimum at S14 and S15 away from the fish nest. W varies significantly in space, ranging from the orders of 10-8 to 10-4. Especially W takes the minimum values at S1 and S5 within the fish nest, white the maximum at S13 and S15 away from the fish nest.

The relationship between the time-averaged current velocity, 0V , and the degree of turbulence, K in Groups 1 and 2 is

shown in Figure 5. Values of 0V in Group 1 tend to be small, and K is inversely proportional to 0V . The relation between

0V and W and that between K and W are given in Figures 6 and 7, respectively. From these figures, it is found that the

fish energy expenditure is reduced in Group 1 comparatively and 0V affects W more significantly than K , which means

the influence of turbulence on the energy expenditure is not critical.

The t-test is used to detect significant differences on TKE, K and W between Groups 1 and 2 using SPSS Statistics (IBM). The number of samples are 38 and 24 in Groups 1 and 2, respectively. In Group 1, TKE and W are found significantly low (p < 0.001), whereas K is high (p < 0.001). Therefore, the artificial fish nest installed in Section 1 is considered effective in reducing fish energy expenditure.

Figure 4. Components of instantaneous current velocity at the point of 80% of the water depth at S11 on 24 April 2014.

4.8

-0.2

-0.1

0

0.1

0.2

0.3

0.4

0 200 400 600 800 1000 1200 1400 1600 1800 2000 2200 2400

ui vi wi

Sampling number

Inst

anta

neo

us

wat

er v

elo

city

~ ~ ~


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Figure 5. Relation between time-averaged current velocity and degree of turbulence.

Figure 6. Relation between time-averaged current velocity and fish energy expenditure.

Figure 7. Relation between degree of turbulence and fish energy expenditure.

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

0 0.1 0.2 0.3 0.4 0.5

In and around fish nest

Away from fish nest

Time-averaged current velocity V0(m/s)

Degre

e o

f tu

rbule

nceK

0

0.0002

0.0004

0.0006

0.0008

0.001

0.0012

0 0.1 0.2 0.3 0.4 0.5


Away from fish nest

Time-averaged current velocity V0(m/s)

En

erg

y e

xp

end

itu

reW

(J)

0

0.0002

0.0004

0.0006

0.0008

0.001

0.0012

0 0.5 1 1.5 2


Away from fish nest

Degree of turbulence K

En

erg

y e

xp

end

itu

reW

(J)


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Table 1. Ranges of observed hydraulic variables, estimated turbulent indices, and estimated energy expenditure for three observations (* ‘d’ means a lower monitoring point at the spot.).

Observation 1 10 October 2013

Observation 2 24 April 2014

Observation 3 16 June 2014

Water depth (m) 0.124(S13)~0.434(S8) 0.200(S13)~0.535(S10) 0.150(S15)~0.475(S7,S10) V0 (m/s) 0.00805(S1)~0.399(S13) 0.00976(S1)~0.429(S15) 0.0105(S4d*)~0.416(S13) TKE (×10-5 m2/s2) 5.9(S1)~250(S12) 10(S6d*)~290(S11) 1.3(S5d*)~400(S12) K ( − ) 0.10(S15)~1.4(S9) 0.12(S15)~1.9(S1) 0.11(S14)~1.2(S2)

W (J) 4.0 ×10-8(S1)

~7.7 × 10-4(S13) 1.3 ×10-7(S1)

~9.7 × 10-4(S15) 4.0 ×10-8 (S5d*) ~8.9 ×10-4 (S13)

5. CONCLUSIONS

The effectiveness of the artificial fish nest in the agricultural drainage canal is investigated by observing the instantaneous current velocity at the points in and around the fish nest, Group 1, and at the points away from the fish nest, Group 2. The turbulent kinetic energy, the degree of turbulence, and the fish energy expenditure computed for each monitoring point reveals that each index is significantly different between Groups 1 and 2. The estimated fish energy expenditure in Group 1 is significantly small even though the degree of turbulence in the group is high. Thus it can be concluded that the fish nest installed is useful for fish to take rest in and around the fish nests. In the future, the effect of degree of turbulence and other turbulence indicators such as eddy and Reynolds shear stress on fish in the canal should be studied to obtain practical knowledge for designing more effective fish nests.

ACKNOWLEDGMENTS

The authors wish to thank Yasufumi Kawamata, Tomoya Minakawa, Shu Ishizaki, Shoko Okano, and Naoko Yamagata for their help in the collection of hydraulic data. Miho town office in Ibaraki Prefecture provided maps of canal in the study area. This study was supported in part by JSPS KAKENHI Grant Numbers 25450353.

REFERENCES

Enders EC., Boisclair D., and Roy AG. (2005). A model of total swimming costs in turbulent flow for juvenile Atlantic salmon (Salmo salar). Canadian Journal of Fisheries and Aquatic Sciences, 62, 1079-1089.

Lupandin AI. (2005). Effect of flow turbulence on swimming speed of fish. Biology Bulletin, 32 (5), 461-466. Pavlov DS., Lupandin AI., and Skorobogatov MA. (2000). The effects of flow turbulence on the behavior and distribution of

fish. Journal of Ichthyology, 40 (2), S232-S261. Santos JM., Silva A., Katopodis C., Pinheiro P., Pinheiro A., Bochechas J., and Ferreira MT. (2012). Ecohydraulics of pool-

type fishways: getting past the barriers. Ecological Engineering, 48, 38-50. Silva AT., Katopodis C., Santos JM., Ferreira MT., and Pinheiro AN. (2012). Cyprinid swimming behaviour in response to

turbulent flow. Ecological Engineering, 44, 314-328. Tharme, RE. (2003). A global perspective on environmental flow assessment: emerging trends in the development and

application of environmental flow methodologies for rivers. River Research and Applications, 19, 397-441. Yi Y., Wang Z. and Yang Z. (2010). Two-dimensional habitat modeling of Chinese sturgeon spawning sites. Ecological

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