22nd IAHR
IAHR-APD
APD Congress,Congress 2020,2020 in Sapporo,Sapporo Japan

ADAPTIVE UNIFORM AND NON-UNIFORM CONFIGURATION OF BOULDERS ON BLOCK RAMPS FOR RIVER RESTORATION
3NNgangbambRomejiRji1, Zulfequar
Z lf
Ahmad
Ah d2 andd Nayan
NSharmaSh

T bl 1.
Table
1 RangeR g off th
the ddatat collected
ll t d ini th
the experimentalp it l studyt dy

1 0 INTRODUCTION & REVIEW OF STUDIES
1.0Blockk rampsBl
p are a ppromising
i i g andd cost-effective
t ff ti structuret t
i riverinirestorationt ti pprojects.
j t TheyTh y are adopted
d pt d ini pplace
lof traditional hydraulic structures because of their ability to sustain the morphological river continuity.
continuity Blockramps are characterized with high turbulent flow on large roughness elements resulting in substantial energy
dissipation In practical applications,dissipation.
applications block ramps are generally made of boulders with mean diameter between
0 3 m and0.3
d 1.5
1 5 m. Fig.1
Fi 1 shows
ha typicalt i l block
bl k ramp application.
li tiBBasedd on experimental
p it l study,t dy, Pagliara
P gli
andd Chiavaccini
Chi
i i ((2006a)(2006 ) have
hproposedpp
d a relationl ti
t computetop t thethrelative energy dissipation on smooth ramp and ramp with base material.
material Further the same authors (2006b)
also proposed a relation for computing the relative energy loss on block ramps with boulders in row and randomarrangements as given by Eq.
Eq (1).
(1) :hCBCSΓ  ……………… (1)H ΔE  A  1  A e
1rBB E  FΓ Fig.1.
Fig 1 A typical Block Ramp Application (Rock Ramp Fishway)
on Goulburn RiverRiver, Victoria (© ResearchGate)

where,here, ∆E = ((Eo – Et);) Eo = upstream
pstream energy,
energ
energ
ramp
flo ;
pgy, Eo = energy
gy at the toe of rampp Et; H = heightg of the ramp;p; hc = critical depth
p of flow;
A B,
B C are coefficients,coefficients which depend on the scale roughness of the flow over the ramp.
ramp For hc /d50 <S = slope of the ramp; and A,
2 5 A = 0.33,0 33 B = -1.3,-1 3 and C = -14.5;-14 5; for 2.5
2 5 < hc /d50 < 6.6,
6 6 A = 0.25,
0 25 B = -1.5,-1 5 and C = -12; and for hc /d50 < 6.6,
6 6 A = 0.15,
0 15 B = 2.5,
1.0, and C = -11.5.
11.5. where, coefficients E and F are functions of arrangement and roughness of the boulders. For randomarrangement
gt andd roundedd d bouldersb ld(i , river((i.e.,istones),t),) E = 0.6
0 6 andd F = 13.3;
13 3; forf row arrangement
gt andd roundedd d boulders,b ld , E=E 0.55
0 55
and F = 10.5,
10 5 and so forth.
forth

Ahmad et al.,al (2009) developed a relation for the estimation of energy loss for block ramps with staggered
arrangements of boulders on base material within a ±3% error limit as given by Eq.
Eq (2) for which R2=0.75:=0 75:

E rB   A  1  A ehH B CS  cΓ10.
9 0 .6  7 .9 ( D B / h c ) Γ 2.0
20 OBJECTIVES OF THE STUDY
NU configuration of the boulders has been so far not investigated by previous researchers.
researchers The study is primarily
concentrated to simulate the effect of various permutations and combinations of macro-roughness boulders undermainly staggered arrangements,arrangements on varying ramp slopes under both uniform and non
non-uniform
uniform (NU) configurations in awider range of test conditions (Γ,(Γ DB, Q,Q Sx, Sy, etc) so as to ascertain the variation in resultant energy dissipation,
dissipation whichshould reinforce
fin formulatingfadaptive design application off block ramps forf stream restoration and related works.
3 0 EXPERIMENTS AND DATA
3.0

3.1
31 Configuration and distribution of macro-roughness boulders
In the present study,
study the staggered pattern in uniform and non
non–uniform
uniform
arrangement of boulders along the L
L-sectionsection of the ramp flume has
been investigated as depicted in Fig. 3.
3 The boulders were placed onth block
thebl k ramp ini variousiconcentrationst ti(Γ) underd variedi d longitudinallit di lspacingspac
i g (Sx) aandd transverset a s e se spacspacingi g (Sy) ini sstaggered
tagge edd aarrangementa ge e tover theth basebmaterial.
t i l A sett off uniform
ifspacingp i g off bouldersb ldwereexamined followed byy non-uniform
non uniform spacingpg ((in terms of longitudinal
gspacing
pg sx and transverse spacing
pg sy)).

Parameter

Unit12
3
45Discharge (Q)Head at Bendmeter (∆h)( )Upstream head (h0)D th att dDepth
downstream
tttoe (ht)Base material size (dxx)

m3/s
mmm
m

Range of data for ramp bed slopes:
1V:5H
1V:7H
1V:9H
0 0073 – 0.0308
0.00730 0308 0.0128
0 0128 – 0.0339
0 0339 0.0176
0 0176 – 0.0387
0 03870.0037 – 0.0753 0.0122 – 0.0919 0.0236 – 0.1209
0 0504 – 0.1223
0.05040 1223 0.0807
0 0807 – 0.1625
0 1625 0.1057
0 1057 – 0.1859
0 18590 0095 – 0.0565
0.0095
0 0565 0.0185
0 0185 – 0.0728
0 0728 0.0226
0 0226 – 0.0591
0 0591
0 016 – 0.025
0.016
0 025
0 016 – 0.025
0.016
0 025
0 016 – 0.025
0.016
0 025

6m

0.042 – 0.100

0.042 – 0.100

0.042 – 0.100

7

Boulder size ((DB)(macro roughness)(macro-roughness)
Boulder concentration ((Г))%

7.76 – 32.07

13.72 – 28.74

16.52 – 28.86

8R
Reynolds
ld N
Numberb (Re)(R ) (×10( 104)

–2 55 – 7.47
2.55
7 47

4 55 – 9.29
4.55
9 29

5 86 – 10.68
5.86
10 68

5.0
5 0 CONCLUSIONS:The existing relationships and parameters for energy dissipation
on block ramps were tested using the collected dataset and theifd havehb(Fig 7 andd 8).
8))
congruities
g iti or variances
foundbeenreportedp t d ((Figs.
q 3)) is pppg criteria and for(Eqbo lder spacing
A relation ((Eq.
proposedfor boulder
computing ∆ErB for block ramps with boulders in staggered uniformand NU configurations (within ± 5% deviation margin).
margin) The Reynolds
no ranged from (2.55(2 55 to 10.68)
10 68) × 104 with a distinct association with∆ErBB for each tested slope; Froude no ranged from 1.64
1 64 to 3.98
3 98 andh d low
hadlcorrelationl ti withith ∆ErB.
A thresholdth h ld boulderb ld concentrationt ti
was found
fd tot beb ini theth range
g0.22g((0.080 22 – 0.25
0 25 for the tested configurations(0 08 ≤ Γ ≤ 0.32)
0 32)) was foundoptimal for imparting efficient energy dissipation.
dissipation
Adaptive relations (Eqs.
(Eqs 4 and 5) have been formulated andproposed for computation of ∆ErBB on block ramps with staggered
arrangement of boulders for both uniform and NU configurations. Therelationl ti
can beb usedd satisfactorily
ti f t il within
ithi ± 5% error limits
li it forf thethg Γ = 0.17
0 17 – 0.30
0 30 andd 0.05
0 05 < hc//H
0 29range
H < 0.29.

Fig 5 Variation of ∆ErB along
Fig.5.
g the ramp
p with DB = 0.055m at Q ≈ 0.025 m3/s ((1V:5H))

R l ti
Relativeenergy dissipation
di i ti( b(observedd ∆ErB) on ramp slopel
1V 5H 1V:7H
1V:5H,1V 7H
andd 1V:9H
1V 9H forf eachh respective
p ti
b ld underboulder
d varied
i d concentrationst ti
anddspacing
spacing,p
g are pplotted with respect
pto the ((hc /H)) as ggiven in Figures
g6a to 6c.
6c
The plots were presented in respect of the boulder longitudinal spacing anddistribution along with Γ and ψ.
ψ Closer spacing and certain non-uniform
configurations exhibited higher dissipation of energy.
energy Also biggerbigger–sized
sizedboulders tend to produce higher ∆ErB it may be noted that for someconfigurations,cofigu attio s, boub ld
boulderde ssizes
i es ooff 00.080
080 m ddia etediametert p
produced
oduceddd sslightly
lightlt y lower
lo eenergygy dissipation
di ip tias comparedp d tot thatth t p
produced
dd byby theth smaller-sized
lli dboulders of 0.055m
0 055m or 0.065
0 065 m diameter.
diameter There is negligible
g geffect of Γ with
the 0.100 10 m size boulders,boulders on the energy dissipation.
dissipation ψ inversely varies withΓ and indicated that lesser values yielded higher energy loss with boulders
Γ,of 0.042m
0 042m diameter and a reverse case was observed with the larger
larger-sized
sizedb ldboulders
off 0.065m
0 065 andd 0.080
0 080 m.

CED, National Institute of Technology Manipur
CED
Manipur, Imphal – 795 004,004 INDIA; ngromezi@gmail.com
ngromezi@gmail com
2 IAHR Member (I-7687),(I 7687) Professor,Professor Dept of Civil Engineering,Engineering Indian Institute of Technology Roorkee,
Roorkee Roorkee – 247667,247667 Uttarakhand,
Uttarakhand INDIA
3 Professor,
Professor CTRANSCTRANS, Indian Institute of Technology Roorkee,
Roorkee Roorkee – 247667,
247667 Uttarakhand,
Uttarakhand INDIA

Fig.8.
Fi
g 8 Comparison
C p i
off ∆EErB computed
p t d usingi g
Eq (5) &relations by other investigators
Eq.

Fig.7. Comparison between ∆ErBB (observed)and ∆ErB (calculated) as per Eq.(5)Eq (5)

Fig 2 Experimental set-up
Fig.2.
set up of the study

Fig 3 Non-Uniform
Fig.3.
N U ifarrangementg
off boulders
b ld
3.2 Data characteristics
Th experimentalTheit l dataset
d t
t for
f variousiconfigurationsfiti
off blockbl k ramps investigatediti t d ini theth presentt studyt d wererecordedd d forf variousiflflow
conditions.
diti
Th experimentsTheit entailed
t il d a range off flows
flwithith Reynolds
Rld numberb off
25,500 to
25,500t 106,800
106,800 underd 3 ramp
p slopesl p with
ith variedi d boulderb ld spacingp i g andd arrangement
gt covering
i g Sx/DB = 1.0
1 0 tot
4 0 ((as shown4.0hi TableinT bl 1).
1))
1 IAHR Member (B(B-65814)
65814), Asst.
Asst Professor
Professor,

4 0 DATA ANALYSIS & RESULTS:
4.0
Boulders of mean diameters 0.042m, 0.055m, 0.065m, 0.080m and 0.10m
wereunderspacing
configuration
overe e tested
testedduded varied
a iedd spaci g ini sstaggered
tagge edd cofigu atio oe thethe threeth ee
ramp
thanthep slopesl p(fig 4((fig.
4))). OnO steept p slopes,
l p , theth normall depthd pth isi lesslththy
critical depth,
depth so the flow profiles do not follow the ggeneral hydraulicasymptotes; there is a gradual dispersion of energy as flow tumble
downstream on the ramp in a waveform profile due to the effect of localized
jumps imparted by the tumbling flow regime as shown in Figure 5.
5…………...(2)IIn thisthi equation,ti
Γ varies
i fromf
0 074 to0.074
t 0.21
0 21 andd DB/hC fromf
0 506 to0.506t 2.307.
2 307 TheTh values
loff coefficients
ffi i t A,
A B,
B andd C will
ill beb
assigned
ig d as suggested
gg t d by
by Pagliara
P gli
andd Chiavaccini
Chi
i i ((2006b).
(2006b))Different studies have been conducted in order to determine a relationship between the energy dissipation and thecharacteristics of the ramp in various designs (Robinson et al.
al 1997,
1997 Pagliara and Chiavaccini 2004,
2004 2006a,
2006a 2006b; Janisch andWeichert 2006; Pagliara et al.,Weichert,
al 2008; Ahmad et al.,al 2009; Oertel and Schlenkhoff,
Schlenkhoff 2012).
2012) Schleiss and Dubois (1999) proposed arelationl ti tot computep t headh d losslf sheetforh t or skimmingkii g flow
fli andind over macro-roughness
ghelements
lt forf bothb th laminarl iandd turbulentt b l tflows when the depth
p of water is significant
gwith regard
gto the roughnessgfactorfactor.

Experimentspwere carried out at the Hydraulics
yLaboratoryy of
Department of Civil Engineering,Engineering Indian Institute of Technology
Roorkee Roorkee on a rectangular ramp of flume width 0.30
Roorkee,
0 30
m at slopesl(S) 1V:4H,
1V 4H 1V:5H,
1V 5H 1V:7H
1V 7H andd 1V:9H.
1V 9H Semi
S iSemi–h i ph i l blocks
hemispherical
bl k withith diametersdit
ranging
gi g betweenb t
0 042 m0.042
to 0.10
0 10 m,m representing boulders with protruding part equal tohalf the diameter,
diameter were placed on the rough ramp bed (Fig.2).
(Fig 2)
The rough bed composed of a uniform layer of river bedpebblespbbl off mean diameterdit d50 = 0.018
0 018 m.

Fig.4.
Fig 4 A typical block ramp in theepe e ta flumeu eexpermental[Hydraulics LabLab., CED
CED, IIT Roorkee]

Sl1.11DBΓ calcl  0.86 
 …………..… ((3))
 2(S x  D B ) (S y  D B )  hc 
ΔE rBB   0.151  1.826   1.386Γ   1.411ψ  …… ((4))
H


a2
Δ E rB  L R  a 1 expp ...……….… ((5))
 a 3   h c / H  2

Table 2.
2 Summary of Experimental test results on Boulder Block Ramps

Fig 6. VariationFig.
V i ti off ∆ErB forf DB = 00.055
055 m iin uniform
if& non-uniform
if
configurations
fig tion ramp
p slopes:l p(a) 1V:5H
1V:5H, (b) 1V:7H
1V:7H, and (c) 1V:9H

Subjective examinations show that the relative energy dissipation decreases as theslope gets flatter.
flatter If the upper limits of the ∆ErB are taken for each slope,slope then it can beconcluded that there is an overall 10 % increase in the energy dissipation whenboulders are placed in staggered configurations over the block ramp.
ramp Also,
Also this scale
seemedd tot amplify
lif withith decrease
di slopeinl
as was marked
k d byb a 14 % increase
if theforth
1V 9H slope.
1V:9H
l p TheTh overallll summaryy off theth testt t results
lt are ppresented
t d ini Table
T bl 2.
2PParameter
t

1V 5H
1V:5H

1V 7H
1V:7H

1V 9H
1V:9H

Γ0 08 – 0.32
0.08
0 32

0 14 – 0.29
0.14
0 29

0 19 – 0.29
0.19
0 29

hc /H

0.048 – 0.125

0.111 – 0.190

0.179 – 0.261∆ErB

0 726 – 0.927
0.726
0 927

0 742 – 0.833
0.742
0 833

0 671 – 0.769
0.671
0 769

T bl 3.
Table
3 VValues
loff coefficients
ffi i t tot beb adopted
d pt d in
i Eq.
Eq (5)( ) ffor range
g off ΓSl

Γ

coefficient a1

coefficient a2

coefficient a3

R2

1

0.17 – 0.19

0.110

0.053

0.064

0.98

2

0.20 – 0.21

0.020

0.834

0.332

0.99

3

0.22 – 0.240.051

0.323

0.207

0.96

40 2 – 0.26
0.25
0 26000.074

01 30.173

01 00.140

0 98
0.98

50 27 – 0.30
0.27
0 30

0 012
0.012

1 616
1.616

0 530
0.530

0 99
0.99

AC
CKNOWLEDGEMENTS
OGS
The author deeply expresses his thankfulness to the Staff and Assistants of the Hydraulics Lab.,Lab Dept.
Dept of Civil Engineering,Engineering IIT Roorkee for their kind coco
operation during the experimental work.
work The author regards the valuable guidance from his Supervisors (2nd and 3rd Authors).
Authors) This study was part and partial ofth research
thehpprojectj t fundedf d d byby theth Indian
I di National
N til CommitteeC
itt on Hydraulics
Hyd li ((INCH),(INCH)), Ministry
Mi i t y off Water
W t Resources
R, Govt.
G t off India.
I di