Development of a Teaching Exercise for the Design of a Revetment

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Prepared by: Dwi Jokowinamo January 1999 Individual Study

Master of Engineering Prograrnme

Development

of a Teaching Exercise

for the Design of

a Revetment

lHE

Il

DELFT

International Institute for ,

Infrastructural,Hydraulic and Environmental Engineering

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Individual Study

Development of A Teaching Exercise

for The Design of A Revetment

by

Dwi Jokowinarno

Supervisors Ir. Benk Jan Verhagen

Ir. Wout de Vries

Departmentof Hydraulic Engineering,

International Institute for Infrastructural,Hydraulic and EnvironmentalEngineering,

Delft,The Netherlands

January, 1999

II

l

le

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INTRODUCTION

The Development of a Teaching Exercise for The Design of a Revetment individual study report is prepared as a requirement for awarding a Master Engineering degree of the International Institute for lnfrastructural, Hydraulic and Environmental Engineering,Delft,the Netherlands.

This individual study report contains educational material to be used at university level in Indonesia. In order to illustrate this development of a teaching exercise,the problem example of revetment design with rip-rap at the estuary of the Musi river has been used and a possible solution for this problem has been given. Actually,rip-rap is only one of the materials that can be used as revetment. Asphalt, concrete blocks, grass are examples of the other possible solution of revetment materials.However, detail reason how to make choice of possible solution was not requested in this exercise.

The content of this exercise is given after the student has received a lecture about the design of a revetment on a dike.The list of questions is given as a guide to solve the exercise. This list of questions is related to the attainment targets of determining boundary conditions and designing arevetment. The question word ''why'' is applied in order to stimulate the student to understand the reason behind the design story. As much as possible real data has been used in this exercise. When data was unavailable, some assumptions have been made by using knowledge of the area and engineering feeling.

I would like to acknowledge the people who have participated in this study for their time,interest, support and concern:

• Ir.Henk Jan Verhagen, Ir.Wout de Vries for their guidance, advice and discussions as supervisors of this individual study

• Ms. Lauren Morgan for her help with improving the English matter of this individual study.

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l.GENERAL

1.1. Objectives

Objectives ofthis Master Engineering work are to:

a. Identify a problem related with coastal defence.

b. Understand how to determine the boundary conditions and apply this knowiedge.

c. Understand the choice ofthe solution.

d. Understand how to design a simple revetment with rip-rap as one of the coastal defences.

e. To develop educational material to be used at university level in Indonesia. 1.2. Attainment targets

1.2.1. Determine boundary conditions (Ioads)

a. The student can estimate the probability of certain wind speeds, using limited data.

b. The student understands the return period of the river discharge and its relation with water level.

c. According to land use information, the student can determine the allowable return period of the water level in a certain area.Determine the return period of the water level in the estuary area and its relation to the return period of river discharge,tidal wave,and the wind speed.

d. Using the map,the student can determine the effective fetch length.

e. The student can calculate wave height and period using a simple wave growth model (Brettschneider model).

f The student can calculate the magnitude ofwind set up.

g. The student is able to assess the reliability of the boundary conditions in relation to the design criteria.

h. The student bas to understand the general failure mechanisms of arevetment, and from that he/she is able to determine which boundary conditions are relevant, and which calculations are relevant.

1.2.2. Design

a. The student should understand why the design water level, varration in water levels,and waves (natural boundary conditions) are important when calculating the design criteria.

b. Inorder to determine the design water level, the student needs to determine the following:

• Reference level (e.g.mean sea level) • Tidal difIerence

• Sea level rise

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Development of a teaching exercise for the design of a revetment

• Gustbump and seiches.

• Wind set up

c. In order to determine the design height of the crest level, the student need to add the following tothe design water level:

• Run up,or overtopping-height • Settlement of subsoil

The run up and settlement is calledfreeboard.

d. Using the «Van der Meer formulae", the student will determine the weight of the rip-rap for the armour layer, filter,and core.Inorder to give the fust insight about the weight ofthe armour layer,the''Hudson formula" can be used.

e. The student should understand the interaction between natura} boundary conditions and the structure.Furthermore,the student should understand how to reduce run up (for instanee using a berm), determine the slope, and identify the part of the slope that needs to be protected by the revetment.

f The student should be aware of the special features of the revetment like toe proteetion and transition area,it should be included in the design.Furthermore, the student should know how to design it.

g. The student, in the design, will show herlhis understanding that the revetment should be easy to be constructed and maintained.

h. The student should know how CRESS can be used to determine the boundary conditions and design criteria.

i. The student will design arevetment.

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Development ofateaching exercise for thedesign ofa revetment

2. PROBLEM

EXAMPLE

In order to illustrate the development of a teaching exercise for the design of a revetment,the problem example of designing arevetment with rip-rap at the estuary of the Musi River is given as follows:

2.1. General

Palembang City, the capitalof the South Sumatra Province, Indonesia and Palembang Port are located along the Musi River, they are currently about 100 km from the estuary (Figure 1, Appendix 1). There are many industrial facilities, such as the refineries ofPertamina (National Company on Oil and Gas Exploration) at Plaju and Sungai Gerong, the large Pusri (Pupuk: Sriwijaya) fertilizer complex, plywood factories, rubber processing plant, shipyards,and so on.

Palembang Port is able to accommodate the ships of various sizes, especially the oil and fertilizer vessels.Those vessels sail from Palembang Port to the open sea and vice versa, follow the Musi river. As the watershed area of the Musi river has lost some of its original vegetation, it is capable of increasing the surface run off in that area.

2.2. Description of study area

In order to proteet the area beside the estuary of the Musi river from the flooding, there is a plan to build a dike and revetment. One Dimensional Mathematical Modeling Study of TidalantiSalt Intrusion in Relation to Sedimentation at the Estuary ofthe Musi River, Indonesia has been carried out by Ferialdy Noerlan (M.Sc. Thesis lliE Delft, 1989). The study area comprises the Musi river from the Port of Palembang to Tanjung Buyut, including its tributaries, the Upang river and the Telang river. This area is located between 2°19' S and 2°59' S,and between 104°46' E and

104°59' E, or between the city of Palembang and Bangka strait.

The distance from the Palembang Port to Tanjung Buyut is about 100 km.The width of the Musi river varies roughly from 400 m to 2000 m at the estuary, and the natural depth mainly varies from 5.0 m to 15.0 m below LWS (low water spring).The Telang river is deeper and narrower than the Musi River, the average width is about 300 m and the average depth is about 10 m below LWS. For the Upang river, the average width is about 500 mand the average depth is about 8.0 m below LWS.

Around the Musi river is swamp lowland which has been developed for agricultural purposes. In this area, there are many irrigation and drainage canals, which were made artificially for these purposes.Besides that, along the Musi river there are many small tributaries and tidal creeks that have been formed in a natural way.

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Development of a teaching exercise for the design ofarevetment

The Musi river has by far the largest discharge in South Sumatra.The springs of the river are situated in the mountains of Sumatra and has a catchment area of about 53,000km2. The yearly average discharge is estimated to be about 2,500m3/s. Little is

known about the discharge characteristic. As data for this exercise, the peak water discharge ofthe Musi river (measured around delta Upang) for each return period is described in Table 1.

T bl 1 Th M_{a e} _e USI..nver pe sc arge

Returnperiod Peakdiscbarge

(years) .... .(1I13/s) 1 4,000 5 5,000 10 6,500 50 8,500 100 12,000 akdi h

2.3. Tides and Water Levels

In the study area, the character of the tide changes during the year between diumal and semi diumal. Along the East coast of Sumatra, the character of the tide changes from purely semi diumal along the Northem part to purely diurnal along the coast of South Sumatra. In the mouth of the Musi river, during spring tide the character is diumal and during neap tide the character is semi diumal. The average tidal range varies from about 3.80 m during spring tide and 1.0 m during neap tide. As the example ofthe tidal measurement, can be seen Figure 2,Appendix 1.

The normal current in the lower Musi river is about 3 kmIhr (0.8 mis) during dry season and 4 km/hr (1.1 mis) durin~ the wet season.The maximum discharge during tidal cycle varies between 10,000 m Is at spring tide and 4,000m3/s at neap tide. The mean water level (Ss) in a given location on a tidal river or estuary is established by averaging water levels during a period of time at that location.The minimum time period considered necessary for evaluating mean water is 15 days, although a longer time period is preferable.Inorder to obtain the absolute difference in elevation of the mean water level at different locations along the river,MWL was calculated along the Musi river from Tanjung Buyut up to Palembang. This measurement established the difference in elevation of the zero readings on the tidal gauges. There is a gradient of MWL from 'Boom Bam' to the Tanjung Buyut . The MWL level at Boom Bam (Palembang) is 1.64 m higher than at Tanjung Buyut.The longitudinal profile of the Musi river can be seen in Figure 3,Appendix 1.

The relation between the discharge and water level can be found by using a rating curve. According to river discharge (suppose that measurement take place during tidal height equal with MSL),as data in this exercise the water level(taken from MSL) can be found as follows:

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Development ofa teaching exercise for thedesign ofa revetment

Table 2 The Musi river water level.

Returnperiod Peakwaterlevd

(years) (m) 1 2.4 5 3.0 10 3.4 50 4.3 100 4.9

The Bangka strait lies between the island of Sumatra and Bangka. The topography of this strait can be seen in Figure 4,Appendix l.5 km from the Tanjung Buyut is 10.3 m below HWS, and from 5 km until 20 km is about 12.8m, and for the rest up to Bangka become shallower again.

The wind velocity record is as follows: T bl 3 Tha e ewm. dspee excee ancesd d

Wind direction from 10 mis 15 mis

N 0.03 0.0006 NE 0.04 0.0015 E 0.07 0.009 SE 0.06 0.005 S 0.02 0.002 2.4. Geotechoic

As a swampy area, the soil category is a soft soil. Primer consolidation of the soil is quite small, and the secondary one is relatively large in the long duration. By means of compaction work, the settlement can be minimised. The amount of settlement is expected to be about 0.50 m in 50 years.

A souree of stone is available 30 km from Tanjung Buyut. The cement factory is further away from the location. Thus, the rip-rap is the most economie choice,

compared with the other revetment material. 2.5. List of questioos

In order to design arevetment with rip-rap,the following list of questions can be used as a guide:

a. Why is the estuary area more vulnerable to flooding than the river?

b. Why should the return period be different for the crest dike height and the design of revetment?

c. Why is it more complicated to determine the design water level in the estuary area, compared with either the river or coastal area?

d. According to the given wind exceedances and map data, the wave and wind set up growth are relatively small. Change the parameters in such a way that the wave growth and wind set up are higher or lower than previous result.What conclusion can be made from these results?

e. Whatis the importance of water levelfluctuation in the design of arevetment?

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Development ofa teaching exercise for the design of a revetment

f Why are the special elements such as berm construction and toe protection, necessary?

g. Explain the importance of the armour, filter and core layers in relation to the revetment design?

h. Why should the designer be aware of the failure mechanism within the transition area?

i. Why is rip-rap the mostsuitable choice of material for this revetment? j. Which boundary conditions are relevant to the design criteria?

k. How can CRESS be used to determine the boundary conditions and design criteria? 1. Design arevetment with the list of questions above as a guide.

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Development ofa teaching exercise for thedesign ofa revetment

3. PROBLEM SOLVING EXAMPLE

3.1.General

Flooding problems in the estuary area are more likely than in the river area due to several reasons.First, the inundation of the salt water can have negative consequences for the paddy rice and drinking water. Second, the river flood warning is more effective, because of anticipated rainfall or discharge at the upstream point. Third,the water level in the estuary results from a combination of river discharge, tide, wind velocity generated waves, wind set up and so on. On the contrary, the water level of the river is mainly determined by river discharge and the hydraulic characteristics of the river.

Indonesia with 13,000 islands has an extremely long coast line,in the order of 80,000

km. Most of the big cities with large populations lie within the coastal zone. In

Indonesia, a developing country, reliable data about the coastal zone is quite limited.

Generally rainfall and river data, although still not satisfactory, are more readily available than coastal data.Data about wave height, for instance, is quite weak. Based on this condition, in order to predict the wave height,wind data is often used.Finally, the problem solving in this exercise has been based on the limited data, sometimes using assumption and engineering feeling.

In the design of a dike and revetment, some calculation such as design water level, wave height and waveperiod, fiool difference, settlement of subsoil and sea level rise should be done.These requirements are needed in order to determine the crest height of the dike, the upper and lower limit of the revetment, and the dimension of the revetment. The design water level is the summation of reference level (for example mean sea level), tidal amplitude during spring tide (half of the tidal difference), sea level rise, gustbump,seiches and wind set up.Not all of these components will occur in a certain location, on the other hand magnitude of these components are sometimes quite smal1.Different circumstances will give different results. One of the important things is the failure mechanism of the revetment, and from that it can be determined which of the boundary conditions are relevant. The boundary conditions are explained in more detail below.

3.2. Detennine boundary conditions

3.2.1. The exceedance frequency of the wind speed.

The exceedance frequency of the wind speed is important, because the wind wiIl generate the wave and the wind set up. The return period or magnitude of the exceedance frequency of the wind speed depend on land use of the area.

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Development of ateaching exercise for thedesign of a revetment

There is no strict value in orderto determine the exceedance frequency of flooding.In cases of a practical problem the exceedance frequency can be determined by using a definition of the level of important.The land use for port,city and their facilities are obviously more important than forest. Thus,the frequency of flooding that is allowed is dependent on the risk acceptance.

There are many development methods in order to determine the exceedance frequency. In The Netherlands,the return period of flooding of the dike is 10,000 years. In Great Britain has been developed to determine the return period, by calculating the house equivalent (HE).Interms of potential flooding damage,which is taken as a measure of the value of the asset at risk, and HE is defined as the average

annual cost of flooding damage suffered by an average house which is at risk of flooding. For a comparison with land use other than houses, see Table 1,Appendix 2. The standard given in Table 2,Appendix2 is the possible target minimum standard of return period in years for tidal and sea defences in Great Britain.

As a guide the return period of flooding in an irrigation or drainage area is 25 years.

For individual houses it is 50 - 100 years, a complete village is in the order of 500 years. For big cities, industrial areas and other vital areas the return period of a darnage-causing flood should be in the order of 1000 years.

So, in this exercise the return period of 25 years (exceedance frequency =0.04) in

Tanjung Buyut section has been chosen.From the probability paper, the wind speed in this frequency from North direction is as follows: the exceedance frequency for the wind speed of 10 mis is 0.03. This means that in one year, there are 10.95 (or 0.03*365) days that these wind speeds ~ 10 mis occur. So, the 10 mis wind speed from North direction will have a return period of 33.33 years (or 365/10.95).For the return period of 25 years, the wind speed for each direction is as follows (see also Figure 1,Appendix 2):

Table4. The wind speed in return period 25 years

Winddirectiolffrom .•.. Wind speed ...

..• •... (mis).· S 8.5 N ~6 NE 10 E 1l.3 SE 9

The map shows the wave (in this case the wind) from the East direction will predominantly attack the Tanjung Buyut section. So, the 1l.3 mis wind speed from East direction is chosen as one of boundary conditions. The different wind speeds in any direction are small. So, the wind from any direction can generate waves with more or less the same.However,in a large return period such as 1,000 years,there are considerable amounts ofwind speed differences.

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Development of a teaching exercisefor the design ofa revetment

3.2.2.The etTectivefetch length

The effective fetch in a random situation is then equated with a weighted average of the projections on the wind direction of all the fetches.However, the reasonable projections on the wind speed should be taken.It is recommended to neglect fetches with angle

e

> 45°.Inorderto determine the effective fetch inthis exercise the formula below can be used.

LR(e)cos2 e

Fe = (1)

Lcose Where:

Fe =the effective fetch (m)

e

=

angle between the main wind direction andother fetch component

~e)

=

radius of the fetch component with angle

e

.

Using CRESS, see also Figure 2, Appendix 2, the effective fetch length can be determined as follows:

I H E Delft CRESS 6.02

calculation of effective

--223 fetch

+---

output

---+

:öcosU 13.511 -:öcos2Û 12.283 -:öRcosU 375 km :öRcos'U 338 km

:E"e(Savil)effective fetch (Savilles method) 28 km :E"e(Modif) effective fetch (Modified method) 27 km

:

---U R cesU cos'U RcosU Rcos'U

degrees km km km :1 42 34 0.743 0.552 25 19 :2 36 31 0.809 0.655 25 20 :3 30 29 0.866 0.750 25 22 :4 24 27 0.914 0.835 25 23 :5 18 26 0.951 0.905 25 24 :6 12 26 0.978 0.957 25 24 :7 6 25 0.995 0.989 25 25 :8 0 25 1.000 1.000 25 25 :9 -6 25 0.995 0.989 25 25 :10 -12 26 0.978 0.957 25 25 :11 -18 26 0.951 0.905 25 24 :12-24 27 0.914 0.835 25 23 :13 -30 29 0.866 0.750 25 22 :14 -36 31 0.809 0.655 25 20 :15 -42 34 0.743 0.552 25 19

+---+

So, the 28kmeffective fetch length can be taken in this circumstance.

The 28 km fetch length is valid in order to determine either the wave growth or the wind set up.Tanjung Buyut is just facing the Bangka strait. But in some condition, for instanee 40 km upstream, more careful consideration should be taken. Ifthe East wind direction is taken, then the fetch length of the wave growth will be more or less the

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Development of a teaching exercise for thedesign of a revetment

same as the river width. While the fetch length of the wind set up is equal with 28km

in open sea, added by 40 km in estuary. The detailed formula can be seen in 3.2.4.

3.2.3.Determine the wave height, wave period

The wave attack is one of the loads.Waves can be generated by wind, ship induced, coming from far away so-calledswell (very gentle wave), earthquake following by

tsunami, and so on.

• According to the map, it can be seen that Bangka strait is not really an ocean.Itcan be concluded, that inthis case the swell is unlikely to occur.

• The most possibility of tsunami is caused by Krakatau volcano. However, the return period ofthis volcano exploding (more than 100 years) is greater than return period of the dike and revetment design. So, this design is not taken into account the tsunami.

• Detail data about vessels is not available.However, as mentioned in the 2.1 path, Palembang Port accommodates vessel of various sizes daily. Consequently, the ship induced wave should be taken into consideration. Inthis circumstance, the slow large size vessel such as tankers can induce wave in the order of magnitude

1.25 m height.This value is found by engineering feeling only.

• Not only the wind wave is considered in this exercise. Inthe case of wind wave being predominant, then the ship induce wave can be ignored.On the other hand, the design of return period of the dike crest level should be different to the revetment. The main reason is an economie point of view.Inthis case, in order to determine the dike crest level, the 25 year return period is taken, while for design revetment it is a 15 year return period.The rip-rap is available 30 km up stream, so

15 year return period is reasonable from the maintenance point ofview.

The following explanation deals with the development of wind wave computation.In 1952, Brettschneider revised a method, developed by Sverdrup and Munk, called S.M.B method. The significant wave height and the characteristic wave period are defined directly from the given wind velocity, the water depth and the fetch. Infact, this definition is obtained by means of empirically established wave development graph and formula.

The formulae can be simplified.First,dimensionless parameter are used:

H* = gH/(/ T* =gT/U F* =gFIU t* =gtlU d* =gd/[j Where:

Hs

=

significantwaveheight (m)

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Development ofa teaching exercise for thedesign ofa revetment

T

=

wave period (s) F =fetch(m)

d =water depth (m) u =wind velocity (mis)

g =gravitation acceleration (m/s')

t

=

duration of storm

The formulae ofBrettschneider for deep water and a long storm duration, as published in the Shore Proteetion Manual of 1973 are as follows:

H* = 0.283 tanh (0.0125 F*0.42) (2)

T* = 1.2 27rtanh (0.077 F*0.25) , (3)

In 1980 Holthuijsen compared all these formulae and came to the conclusion that the Brettschneider is one ofthe best. For shallow water, with an unlimited fetch, the formulae are:

H* = 0.283 tanh (0.53 doJtfJ.75) T* = 1.2 27rtanh (0.833 d*0.375)

... (4)

... (5)

So, by using the formula (2) and (3) :

IfF* = 24778,thenH* =0.283 tanh (0.0125 * 24778°.42) = 0.19932, andHs = 0.199

*

11.32/10 = 2.54m

It should be noted that this wave is occurring in the deep water. When the water depth reaches the breaking point, the wave height will decrease.

IfT* = 1.2 27rtanh (0.077 F*0.25) = 1.2 *2*3.14tanh (0.077*24778.76°.25) =5.63s,

then T =5.63*11.3/10 =6.36s

By using Formula 4, a wave height of 1.75 m is found. CRESS, On the other hand gives the following results:

T bI 5 Tha e ewave eig. t an .peno or con mo

Wind speed ....'Hs Tp (mis) .Ó. .(m)···.•· ..·· (s) 11.3 1.02 3.8 11.0 0.99 3.8 10.7 0.96 3.7 10.4 0.93 3.7 10.2 0.91 3.6 10.0 0.89 3.6

h . ht and neri dil di n d

=

12.8 m, F

=

28 km, t

=

5 hours

Table 6. The wave height and period for condition U

=

11.3 mis,F

=

28 km, t

=

5 hours

Waterdeptb H. Tp Waterdeptb ·1Is Tp

(m) (m) (s) (m) (ol) (m) 12.8 1.02 3.8 10.4 0.98 3.8 12.2 1.01 3.8 9.8 0.97 3.7 11.6 1.00 3.8 9.0 0.95 3.7 11 0.99 3.8 8.0 0.92 3.7 11 Individualstudyreport

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Development of a teaching exercise for thedesign ofa revetment

The wave height will increase as a result of increasing wind speed, increasing fetch length and in the deep water area.The results above show that the significant wave height does not change considerably if the wind speed has a either 15 year or 25 year return period, or slightly changing the water depth.The different H, due to the wind speed with a return period of25 years (11.3 rnJs) and 15 years (10 rnJs) is in the order of 13 cm.

From Table 6 it can be concluded that different wave heights due to the water depth at HWS (12.8 m) and LWS (9 m) is in the order of less than 10 cm, while the wave period is relatively the same. The peak period is equal to more or less 3.7 Hs.

However, in the case of the wave approaehing the certain shallower condition, the wave height will reduce a considerable amount. The condition of the sea can be classified as shallow sea, so Formula 4 is more reasonable and 1.75 m wave height is chosen. It should be noted that there are no formulae which fully representative of nature. Therefore, results of these formulae give the order of magnitude only.

As mentioned before, the wave height approaehing to the shallower area will be reduced. Using CRESS, the prediction ofthe significant wave height and period in the shallow area can be determined as follows:

First, the 11.3mis wind speed is chosen as input.Water level above chart datum (2.28 m) is summation of tidal amplitude (1.9 m), wind set up (0.18 m, see 3.2.4.), and influence of river discharge (0.2 m). In fact, the peak water level in a 25 year return period is 3.8 m. This value is valid on the condition that the river is the predominant influence. Actually, at Tanjung Buyut location, the river influence has become weak, and 0.20 m is a reasonable value instead of 3.8 m. One dimension model such as DUFLOW can help to solve this matter, but are not be covered in this exercise.

I H E Delft CRESS 6.02 _

2331Calculation of wave energy decay

+_

________________________

input

--

---

-

--

---

+

:Ho Deep water wave height 1.75 m

:Tp Peak period of the spectrum 6.5 s

:PhiOWave angle at deep water 0 degrees

:U Tidal curent velocity 1.1 mis

:Nu Angle of currentvelocity 180 degrees

:Rho Densityof sea water 1020 kg/rn3

:Fw Friction coefficient 0.01

-:Vw Wind velocity

:eta Water level abovechart datum

:Dx Step size parameter (step is L/Dx)

:File for tabular data :

11 mis

2.28 m

25 -*.*

+

output

---

-

---

-

---

+

: distance depth(-) Hs Eta Qbroken Cg Phi V

: mmm cm mis degrees mis :1 20000 -12.80 1.62 227.00 0.000 5.92 0.0 0.00 :2 10000 -12.80 1.58 227.04 0.000 5.92 0.0 0.00 :3 5000 -10.30 1.53 227.010.000 6.05 0.0 0.00 :4 2500 -8.80 1.49 226.99 0.000 6.08 0.0 0.00 :5 700 -6.00 1.47 226.93 0.000 6.07 0.0 0.00 :6 0 -4.50 1.45 226.890.000 6.02 0.0 0.00

+

---

-

---

-

--

-

---

-

----

-

---

-

---

+

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Development of a teaching exercise for thedesign ofa revetment

So, near the construction the significant wave height = 1.45 m (more than a ship induced wave). From this energy decay calculation, the H, is reduced in the order of 30 cm, or remain about 83 % of deep water wave height. Wave run up is proportional with the Hs,consequently by reducing H, the wave run up is reduced.

Second, for the various deep water wave heights due to the different a 25 year and 15 year return periods of the wind speed, it seems that the different H,is in the order of 7

cm. Note, that this value is small. Also, later on the weight of the stone is given in a certain range instead of a certain value.

In summary, the deep water wave height

=

1.75 mand shallow water wave height

=

1.45 m. The peak period

=

6.5 s.

3.2.4. Determine tbe wind set up

UsuaIly, if a big wave occurs, in the same time a big set up will also occur, because both of them are caused by wind.

For lakes and other nearly enclosed water bodies one can use the following formula:

As=.!.Cw Pair *U2F cos<l> (6) 2 Pwater gh

For a semi enclosed bay one may use the same formula, but then one should omit the factor Y2,because in that case there will not be set-down at the downwind side. There is a supply ofwater from the sea.

The solution ofthe differential equation for a tidal shelfis :

tJ.S= 2Cw(Pa/ Pw)u 2F COS<I>+h2 - h. (7)

g

Where:

C;

=

coefficient (0.8*10-3to3*10-3)

pm

=

density ofair(1.25 kg/m") pwatcr

=

density ofwater (1030 kg/m")

U =wind velocity (mis)

F =fetch length (m)

g =acceleration of gravity (m/s') h =water depth(m)

Cl> =angle between wind direction and axis (degrees)

Using CRESS, the wind set up can be determined as follows:

The depth of the bottom in front of the dike at Tanjung Buyut (4.65 m) is the summation of:

2.27 m (the depth ofthe bottom below the MSL) + 1.9 m (HWS tidal amplitude) +

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Development of a teaching exercise for the design of a revetment

0.2 m (influence of water level of the river with a 25 year return period in Tanjung Buyut) +

0.28 m(sea level rise and settlement of subsoil).

Delft --:-__ -,-__ -,--,----_CRESS 6.02

212 Waterlevel changes due to wind set-up

+

---

-

---

input

---

-

--

-

---

-

+

:U windspeed, 10 m above surface 11.3 mis

:h depth of area 5.00 m

:F fetch 28.000 km

:Fi angle between wind and coastline 0 degrees :Ws Width of the shallow section 1000 m

:hs depth of the shallow section 4.65 m

:lake enclosed area (1) or open sea (2)

2-+--- output ---- ---:B windspeed in Beaufort-scale 5 Bft

:dhl wind set-up in the deep area 0.17 m

:dh2 total wind set-up in shallow area 0.18 m

+

---

-

---

-

---

-

---

-

---

-

----

-

--

-

+

I H E

So,the 0.18 m wind set-up is chosen. Incase the location is 40 km upstream from Tanjung Buyut,the wind set up is 0.3 m (0.18 m wind set up in the open sea added to 0.12 m wind set up in the enclosed area).

Inorder to recognise the sensitivity of parameters various calculations using CRESS with the same conditions as the with calculation above have been conducted, and the results can be seen inthe tables that follows:

T bl 7 W' da e in setUP W1 vanous waterde hpt

Waterdepth .Wmdsetup > •. i .Water depth Wiild Sëtup

.(m) . ·i .. ... (ml .. Cm) .. (m)...

8 0.12 5 0.18

7 0.13 4 0.22

6 0.15 3.5 0.25

Table 8.Wind set up with variousfetch length

Feëthleagth I Wind set up. _. Fetchlength Wind setup

(km) ... (m).. (km) (m)

200 1.13 50 0.29

100 0.58 25 0.15

75 0.43 10 0.7

T bla e9.Wm'd set upWIt varrouswind ve oci1 ty

...Wind speed _{Wind Set up} ..

Wind speed Wind setup

.. (mis) (m) (mis) (m)

40 1.99 11.3 0.17

30 1.18 10 0.13

20 0.52 5 0.03

These tables show that the wind setup will reach a higher value in conditions with a longerfetch, higherwind speed, orshallower area. The 0.18 m wind setup suchasin this circumstance isrelatively smalt.Just to give insight, in some conditions suchas

(19)

Development ofateachingexercise forthedesign ofarevetment

on the coast of Bangladesh, due to the huge storm the wind set up can reach in the order of more than 3 m.

3.2.5. Determine the wave run up

The level of the crest of the dike is designed in such a way that an amount of water is still allowed to overtop the dike.Again,there is no strict value of the magnitude of the amount of water that can overtop the dike. Inalldesign itis common useto applythe 2%run up. There is no real physical justification for the number''2''but it is assumed small enough. Inthis exercise,the parameter is included in the calculation to find that the more or less 1l/s/m overtopping is found.

Inorder to reduce the wave run up or overtopping,any kind of method can be used. • Berm

Berm construction is needed in order to reduce the wave overtopping, to provide access to construct therevetment and also for maintenance.Usually berm construction lies on the design water level. Note,that the period of high water is relatively short (a number ofhours), therefore the berm construction functions more as a road.However,

too large a berm becomes ineffective.So, the width of a berm depends on the level of traffic density. For the irrigation area, traffic is not so busy compared with a conneetion road of urban node.

• Slope

A steep slope will reduce the overtopping and reduce the width body of the dike. However,too steep a slope can cause damage to the revetment and even to the slope stability of the dike itself. The angle of outer slope is more gentle than in the inner (rear) side. For practical reasons, slopes are designed not steeper than 1:2.5,because of problems with maintenance.

Incases where an extremely gentle slope occurs,the dimensions of the revetment will become extremely small or the revetment may not be needed any more. This kind of thing can be seen in nature with the dimension of the bottom material of a gentie beach.

• Roughness.

The more rough the revetment,the moreit willreduce wave overtopping. The rip-rap revetment is rough enough, compared to concrete bloek. Later on, using CRESS, the sensitivity of each parameter related with wave overtopping will be found.

Inorder to get insight about the wave run up, the simpIe formula called "Old Delft Formula" can be used. This formula is valid only in conditions without swell (quite gentle wave), without berm, does not deal with various roughness of revetment, incoming wave with perpendicular angle with structure and no information about depth of the bottom infront ofthe dike.Onlytwo parameters are taken into account in this formula, namely significant wave height and slope of the structure.

R2"/& =8H,tan a (8)

(20)

Development of a teaching exercise for the design of arevetment

Suppose that the 1:3.5 slope is chosen. So,R 2%=8*1.45 /3.5 =3.3 m.In the 1:3.5 slope, the body width of the dike in relation with run up will become 11.55 m.

Obviously3.3 m is large number, therefore run up is important in this case. So,the run up computation has to be worked out in more detail with some alternatives in order to reduce run up.

Using CRESS,the height ofthe free board can be determined as follows :

The depth ofthe bottom in front ofthe dike (4.83 m) is the summation of 4.65 m+

0.18 m (wind set up due to 11.3 mis wind speed in the open sea). The 1:3.5 slope is chosen, with a berm and the roughness ofthe rip-rap is 0.55 (more detail see Table 3,

Appendix2):

Delft :-- ---:-:..,..-RESS6.02

242 Calculation of overtopping over a dike

+

---

-

---

-

---

-

input

---

-

---

+

:Hs significant wave height 1.45 m

:Tp peak period of incoming wave 6.5 sec

:beta angle of incidence of waves 0 degrees

:freeboard height of crest above SWL 1.5 m

:nl slope of the construction above berm 1:3.

5-:n2 slope of the construction below berm 1:3.5

-:B berm width 6 m

:d depth of berm below SWL 0.00 m

:nb slope of the berm (horizontal= 0) 1:30

-:gammaf roughness of slope (see table) 0.55

-:crestprm long-crested (0)or short-crested (1) 1

-:dh depth of bottom in front 4.8 m

+

----

-

---

-

---

-

---

-

output ---: :ksi 1.93 -I H E :gamma :alpha :Bopt

reduction coefficients

equivalent slope of construction

First estimate of a better berm width

0.37

-1:3.50

-7 m

:q overflow 1.22 litres!s

+-

---

-

----

-

---

-

--

-

--

-

--

-

---

----

-

---

--

---

+

So,the height ofthe dike is 6.3 m from the bottom or 4.03 m from the mean sea level. Obviously,the berm construction will reduce the wave overtopping. The 5.5 m berm width is sufficient for a truck in order to either construct or maintain the dike.

Furthermore,in order to know the sensitivity of the parameters related to overtopping,

calculation can be conducted in CRESS. Parameters that can reduce overtopping can be put in the following table:

T blOS_{a e 1} _ensmvitv0 .fparameter re ate WItd . h overtopping

Nr. Increasing of Reduce Remark

Parameter overtoooing?

1

H

s No

-2 To No

-3 beta Yes

-4 freeboard Yes too high becomes not economical 5 nl Yes the body of the dike becomes larger 6 n2 Yes the body of the dike becomes larger 7 B Yes too much width becomes ineffective. 8 d No will be effective at sea water level

9 nb Yes more steep willreduce

16

(21)

Development ofa teaching exercise for thedesign of a revetment

10 gammaf No more smooth revetment,willincrease

11 crestprm

-

-12 dh No

-3.3. Design of the revetment 3.3.1.General

Inorder to design arevetment for the dike, suitable selection of the loads and an understanding of the failure mechanisms are very important. Ingeneral, the elements of a sea dike are: toe protection, revetment, berm,upper outer slope, crest,the inner slope and drainage.

• Toeproteetion

First, this proteetion is especially important for situations during low water. During the HWS the water level is much higher and waves will not attack the toe. Second,to prevent scouring by currents (and waves) just in front of the dike. Stones (usually from an old revetment) are often used, also fascine mattress made of brushwood and bamboo.

• The revetment

Inthe zone where wave attack is expected the slope need protection. This can in the form of natural stone,concrete blocks, asphalt, concrete,or even grass (in cases where the wave attack is very minor).

• The berm

As mentioned before, that the main purposes of the berm are to decrease the wave run up,and for maintaining revetment. Therefore it is generally not narrower than 5 mand usually covered with asphalt or concrete block. Experience has shown that a revetment with a length (measured along the slope) of more than 20 m is not serviceable.The slope ofthe berm is very gentle,inorder of 1:20 - 1:50.A horizontal slope is not advisable,because then water will remain on the berm (ponding).

• The upper outer slope.

This part does not suffer from wave impact,but only from the wave run up.Therefore a grass cover is generally sufficient. Inorder to avoid erosion during a design water level wave, thickness of the clay layer below the grass should be sufficient. InThe Netherlands,for example, the thickness of the layer beneath the grass is more or less

0.8m.

• The crest:

From the theoretical point of view the crest width could be zero.Practically, the 2.5 m is taken, otherwise the execution would be very difficult.

(22)

Development ofa teaching exercise for thedesign ofa revetment

• The inner slope

The minimum inner slope is 1:2.5 for serviceability. This part needs no hard protection. In cases where more overtopping is allowed, it is necessary to make a more resistant slope protection.

• Drainage

Itis important that the water can flow out of the dike in a controlled way. Ingeneral drainage can be comprised a simple gravellayer.

From the explanations above, it can be found the design water level, freeboard,

variation of water level, waves, and their interaction with the structural parameters such as slope, roughness, and berm. Summary of the water level and structural parameters can be illustrated as follows:

4,03

2,53 OWL

0,00 MSL

--1,90 LWS -2,27

The tidal range during the springtide is about 3.8 m.The low sea water level is 1.9 m

+run down, below mean sea level. The construction of arevetment can be started trom the low water spring level, namelyat 0.4 m above the bottom.Inorder to proteet the bottom from scouring in front of the transition area, toe proteetion is needed. Not all of the body of the dike need the revetment, only the place which is vulnerable to wave attack. So the dike body piece until3.28 m+MSL (or SWL+0.5 Hs) needs the

revetment.Area above this level is protected enough by grass.

The transition area between the rip-rap and the grass needs special construction in such a way that the hole due to wave attack can be avoided. Otherwise, the wave attack will erode this transition area.

3.3.2.Dimension of revetment

Revetment construction can fail due to wave attack.That is why the weight of the rip-rap should be sufficient. Many methods for rock size prediction of armour units designed for wave attack have been proposed. Some of them are the Hudson formula as used in SPM (1984) and the formulae derived by Van der Meer (1988a).Inorder to gain insight about the weight of the stone,the original "Hudson formula" can be used:

18 Individualstudy report

(23)

Development of a teaching exercise for the design ofarevetment

_ PrH3

M

50 - 3 ,,,, •.• ,,(9)

KDt! cota

Where:

Mso =Mass of unit given by 50% on mass distribution curve

pr =Mass density of rock (saturated surface drydensity)

H

=

significant wave height

Ko =coefficient of stability

~

=

relative buoyant density of material considered

=

p,/pw - 1

a

=

structure front face angle

The main advantages of the Hudson formula are its simplicity, and the wide range of armour units and configurations for which values ofKD have been derived.

While the Van der Meer formulae is as follows:

For plunging waves:

Hs =6.2pO.18(

_

~N

· J°

.l

.;!

(10)

MJnSO \ '" IV

And for surging waves:

Hs =l.Op-o.3(

~NJO

.

2

.Jcota';! (11)

M)nso '"IV

The transition from plunging to surging waves can be calculated using a critical value ofçmc:

ë:

=

[6.2pO.31

Jta;

-

ti

F -

(12)

In which:

DnSo

=

nominal diameter of required stone (50 % passes the sieve)

S =level of damage

N

=

number ofwaves, with maximum value of7700

P =permeability

• The slope is one of the parameters of level of damage.The level of damage is the number that indicates the structure damage. The level of damage in more detail can be seen in Table 4, Appendix 2.

19

(24)

Development of a teaching exercise for the design ofa revetment

• Number of waves N depends on the wave period and duration of the wind blows or storm.If the wave period equal 5.3 seconds, and the storm duration equal 4 hours, then N =4hours /5.3s=2770.

• Permeability P is varies depending on the kind of structure. More detail about P

can be seen in Figure 4, Appendix 2. If the revetment consists of two armour

layers, filter and a core made from impermeable material such as clay, then the

permeability is about of0.1.

The surf similarity parameter (I;) has often been used to described the form of wave breaking on beach structure.

tana

ç =

ff

(13)

Where :1; = 5 is surging; I; = 3 is collapsing; I; = 1.5 is plunging. For this

circumstances, the I; = 0.2857/(1.45/43.8)°·5

=

1.57. So, it belong to the plunging category.

Using CRESS, theDsso can be determined as follows :

I HEDel ft .,.--_-::--:::-:-__ ..,..,..,-_-,- CRESS 6.02

512 Ca1eu1ation of Rip-rap (Van der Meer)

+

---

-

---

input

---

+

:Hs Significant wave height 1.45 m

:Tm Average wave periode 5.3 s

:n slope 1:3.5

-:RhoW Oensity water 1025 kg/m3

:RhoS Oensity of stones 2600 kg/m3

:S Oamage value 4

-:N number of waves (maximum value 7500) 2770

-:P Permeability ot core (valid range U.1-0.6) 0.10

-+

--

---

-

---

output ---:

:Ksi 1.57

-:Breaking breaks (1) or not (0) 1

-:Stabil stabLe (1) or not (0I 1

-:050

:On50 :W50

diameter required stone (50% passes sieve) 0.57 diameter required stone (nominal diameter) 0.48

required weight of stone 294

m m

kg

+-

---

--

---

-

---

+

So,Dsso

=

0.48 m or Wso

=

294 kg. This armour layer is containing two layers. The revetment needs a filter layer. This demand is related to the failure mechanism. The armour layer will not be destroyed by wave attack if the weight of the stone is sufficient. Another souree of damage is due to the uplift pressure. According to previous research, ifthe core is made from the impermeable such as clay, so the Dnso

annor / Dnso filter=4.5 is admitted.The 0.1 m diameter or 3.2 kg of the rock is desired as filter layer.

The thickness of the layers is given by : T = n kt Dn5o.Various n andktnumber can be seen in Table 5, Appendix2. So, thickness ofthe armour layer

=

2*1*0.48

=

0.96 m and for the filter layer

=

0.2m

(25)

Development ofateaching exercise for thedesign of a revetment

In orderto design the toe protection, the magnitude of the still water levelthat causes the largest scouring, is chosen.Inthis case the depth of the bottom -2.27 m +MSL,

while the tidalamplitude during the spring tide is 1.9m.So the low water spring level

is about 0.4 mfromthe bottom.Thevalue of'H, is inthe orderof 1.45 m.

Using CRESS the requirement of toe proteetion can be determined as follows:

I H E Oelft _--::-_---:- --,-_ CRESS 6.02

531 Calculation of a rip-rap toe protection

+

---

input

---

+

:Hs Significant wave height at the toe 1.45 m

:ht depth of toe under still water level 0.72 m

:S Oamage va1ue 4

-:RhoW Oensity of water 1025 kg/m3

:RhoS Oensity of stones 2600 kg/m3

+

---

-

---

-

---

output ---

-:050 diameter required stone (50% passes sieve) 0.37 m

:On50diameter required stone (nomina1 diameter) 0.44 m

:W50 required weight of stone 132 kg

+

---

-

---

-

---

-

----

+

As mentioned before,the dimension ofthe stone is within certain range, instead of a certain value. The table below of standard stone classes according to CUR-CIRIA

154,can be used as guide.

Table 11.Standard stone classes,light and hea"Y_gradings(from C

Range ...

\V

so

·.··.x >iii Dl'i,illl)·· ... ..~ ....

10-60 kg 35 kg 0.23 0.37 60-300 kg 185 kg 0.41 0.66 300-1000 kg 680 kg 0.63 1.01 1-3 ton 2 ton 0.91 1.45 3-6 ton 4.5 ton 1.20 1.92 6-10 ton 8 ton 1.45 2.31 UR-CIRIA 154)

According to Table 11,the range of the rip-rap that can be used in each path is as follows:

From the calculation, the Wsoof armour layer =294 kg, Wsofilter =3.2 kg, Wsotoe proteetion= 132 kg.In this case, the range for armour layer and toe proteetion is too optimistic, so using the stone in the upper limit of the range preferabie. Otherwise,

using 60 kg for armour layer for example, it will be cause a high risk of failure.

(26)

Development of a teaching exercise for the design ofa revetment

3.3.3. Drawing

The cross section of the dike and detail drawing of some dike part can be seen in Appendix 3.

Construction takes place during low water spring and very small wind speed. In Indonesia, it is preferabie to construct revetment during dry season rather than during wet season, because river discharge is very small and there is almost no rain.

Sequence of construction steps is as follows:

a. Build the core, with compaction on it.

b. Build the berm in such a way that access to construct (and later on to maintain) is sufficient.

c. The toe is the foundation of the revetment. Ingeneral it is a row of wooden piles.

Put the rock on the bottom of the sea in front of a row of wooden piles, as a toe protection.

d. Put the filter layer on the dike body in the area which need arevetment.

e. Put the first armour layer just on top of the filter layer and follow by the second armour layer.

f Build the proteetion of the transition area between rock and grass path. g. Build the grass path.

h. Build the berm pavement, and if very urgent also the crest pavement.

22

(27)

Development ofa teaching exercise for thedesign ofarevetment

4. CONCLUSION AND RECOMMENDATION

4.1. Conclusion

a. Using the list of questions as a guide, the student is expected to achieve the attainment targets.

b. The student is expected to understand that the crest of the dike in the estuary of Musi river is design water level added by freeboard. This design water level is the summation of reference level, tidal amplitude, influence of river discharge. wind set up and sea level rise. This freeboard is the summation of wave run up or

overtopping and settlement of subsoil.

c. The student is expected to understand that upper limit and lower limit of the revetment design, the variation of water level, characteristics of wave attack are important parameters.These parameters are related to dimension of revetment and which place that needed arevetment.

d. The student is able to design arevetment with rip-rap on a dike at Musi river estuary and understand that boundary conditions such as wave,variation of water levels,geotechnic aspects,wind set up,wave run up or overtopping are relevant. e. The student can use CRESS as a tool to solve the problem related to the design of a

revetment.

4.2. Recommendation

a. Inorder to achieve better educational material, further study is needed to get more reliable data, especially characteristic of river discharge.

b. As an educational tools, various boundary condition is needed in order to gain various result and better insight.

(28)

REFERENCE

Noerlan, F. :OneDimensional Mathematical Modeling Study of Tidal and Salt Intrusion

in Relation to Sedimentation at the Estuary of the Musi River,Indonesia,

M.Sc Thesis mE Delft,1989

Van der Meer, J.W., and Ligteringen, J :Breakwater Design, Lecture note mE Delft,

1998

(29)

(30)

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(37)

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---

.

----~---lIJ' '<!' C') ~ 0 0 0 0-e r-, -o ~"l -e-v;

~~---

~

--~

~

\

--- :

8_

2

-- 0-- 0--0--0--0--0--i0--0--0--0--0--0--0-- c <, -c ~~ ~ ~ <t ~ ~ cO ~ -~~ ~ ..0 -. -- -e M ~ Ol N EO ,_:_ Ö_~ --, -,-- _-_'!! öï <;I C-o_o M--~--- ---N--~---~--- ---__;_---~--- ---.---'---'--- +-0 0-co --, -o io i -é f- -("') I i- -r N 1- - r-I -i -\ ~~~ ---:$=: -+--+---'---'---\---'-\_---,---~--;-

--+--\

(38)

Q :z <: ...J Vl _z:

"

_"

\ \_,

"

\

"

.... " , -, ,_, ' ,, "

-

<, ".... , " , "_"" " "

_"

-,_, ",-,_, .... ---<,

--

_{'-_---}

_____ ct:)

---

--:::=---...

----I --...

---

__ fl"'\ ---

----~

..

_-_

I , '..__,

'-_

, " "-'----_-

---__ _{____} ---___---a:J"--co __ .... t ---,' _____ ---- 0.. --re:::>

-0---LJj"" '

(39)

fig. b

o,,~AIo..~F :2 o,,~ F/Dn50 C:.c

Dn~o A 'On !loOF: 4.5

fig. d

nofirt.r

noCOI"a

On!loOA: normnc: dlomlrtcrr of ormour StOM o,,!loOF : nomino! diomlrt«r- of firtar matmo! On~oC=nomina! dic!nIftcrr of COI"V

(40)

T bIa e 1 Companson between ot er an use th I d hanh ouses In. Great B·ntam· ~eätUE _. .-

~

l

t

~~

_·

.

-- .:.~_.·,s.P~""·;~~i'àlen1c~ . ..'IlSe_ .. ~. -_ .- ~~. e:~" _ =c= House Number l.0 Garden/allotments Number 0.04 NRP-Manufacturing Area (m') 0.030 NRP-Distribution Area (m2) 0.054 NRP-Leisure Area (m2) 0.032 NRP-offices Area (m2) 0.033 NRP-Retail Area (m2) 0.035 NRP-Agricultural Area (m2) 0.01 C roads Number 2.7 B roads Number 6.3 A roads(non-trunk) Number 15.9

A roads (trunk) Number 3l.7

Motorway Number 63.5

Railwav Number 63.5

Forestrv and scrub Area(100 ha,0.01 km2) 0.02

Extensive pasture Area(lOO ha, 0.01 km2) l.3

Intensive pasture Area(lOOha,0.01 km") 3.0 Extensive arabie Area(lOO ha, 0.01 km2) 6.3

Intensive arabie Area(lOO ha, 0.01 km") 44.1

Formal parks Number 0.6

Golf/race course Number 0.7

Playing fields Number 0.1

Special parks Number 9.2

NRP =Non-resident property

Table 2. The possible target minimum standard (return period in years) for tidal and sea defenses in Great Britain

A

E

Table 3.Roughness values

~tel'iaI .~~

-- ,~

-Smooth concrete and asphalt l.00

Good pitched stones l.00

Concrete blocks (Hanngman) 0.95 Open stone asphalt (fixstone) 0.95

Grass (3 cm long) 0.95

Grouted, rough stones 0.80

(41)

Gabions 0.70 Ripples on slope f7Hs=0.15 0.65

Maximum ripples resistance 0.55

One layer of rip-rap 0.60

Twolavers of rip-rap 0.55 Table4.Level of damaze

1:6 3 8-12 17

~

=

~

ea

i

~

i~~

1:1.5 2 3-5 8 1:2 2 4-6 8 1:3 2 6-9 12 1:4 3 8-12 17

T bI 5 Vala e uesof'k,an n, as givend In. the SPM (1984)

- --_. smooth rock, n=2 1.02 0.38 rouah rock, n=2 1.00 0.37 rough rock, n>3 1.00 0.40 graded rock

-

0.37 cubes 1.10 0.47 tetrapods 1.04 0.50 dolose 0.94 0.56

(42)

(43)

/

.

O

I

KE

C[{OSS

SECTION

(j)

" 4,03 2,53 0,00 - 2,27

G

-3,47 5,30 15,75 _lt_,_O_O

B

5,00 ₁₇₀₀ 4,50 i.,00

NOTA

TI

ON:

1. TOE pnOTE( TJON 2. WOODEN P1LE 3. RIP-nAP nEYETMENT 4. BEru1

5. TRANSJTJON AREA BETWEEN RIP-RAP AND GnASS

6. GnAS3

7. (nEST

8. INNEn SLOPE 9. OnAJNAGE

10.

c

on

E

O\oJL= DESIGN WATER LEV!::L

(44)

DETA

I

L

A

DE

TAIL

[

200- 300 Kg Armour layer

r

10-60 Kg Filter layer

I

0,1-0,3 \ Concrete bloek vitb hole -;-~ 2;3 0,2,2 POL::5/ m \

DETAIL B

5,0 m ToE' Pr ot er tiori

(45)

(46)

IHE

II

DELFT P.O.Box3015 2601 DA Delft The Netherlands Tel. :+31(0)15 2151715 Fax: +31(0)15 2122921 E-mail: ihe@ihe.nl

Development of a Teaching Exercise for the Design of a Revetment

Development

of a Teaching Exercise

for the Design of

a Revetment

lHE

Il