teknik drainasi handout-eng.doc

DRAINAGE ENGINEERING

By: Dr.Ir. Sunjoto Dip.HE, DEA

1.Introduction

a. Terminology

b. Meaning in indonesian

c. Characteristic of inundation

d. Drainage and irrigation

e. Change of land use

2.Occurrence of inundation

a. Impervious area increases

b. Vegetation coverage decreases

c. Sponge system disappears

All of above problems occur as a consequence of the urbanization

Lecture hand out of Drainage Engineering by Dr.Ir. Sunjoto Dip.HE DEA 1/37

Fig. 1. Diagram of water resources devastate as a result of urbanization (Prince, 2000, lecture note).

Hand-out of Drainage Engineering Lecture, Departement of Civil Engineering and Environment, Gadjah Mada University 2/37

URBANIZATION

BUILDING DENSITY

INCREASES

DRAINAGE SYSTEM MODIFIED

DRAINAGE SYSTEM

MODIFIED

IMPERVIOUS AREA

INCREASES

URBAN CLIMATECHANGES

RUNOFFVOLUME

INCREASES

FLOWVELOCITY

INCREASES

PEAK RUNOFFRATE

INCREASES

LAG TIME &TIME BASE REDUCE

FLOOD CONTROL PROBLEMS

POPULATION DENSITY INCREASES

WATERBORNE WASTE INCREASES

WATER DEMAND RISES

WATER RESOURCES PROBLEMS

GROUNDWATER RECHARGE REDUCE

STORMWATER QUALITY

DETERIORATES

BASEFLOW REDUCES

RECEIVING WATER QUALITY

DETERIORATES

POLLUTION CONTROL

PROBLEMS

Fig 2. Diagram of water resources devastate as a result of urbanization and alternative of solution (Sunjoto, 2005)3. Mazhab in drainage scienceHand-out of Drainage Engineering Lecture, Departement of Civil Engineering and Environment, Gadjah Mada University 3/37

URBANIZATION

BUILDING DENSITY

INCREASES

DRAINAGE SYSTEM MODIFIED

IMPERVIOUS AREAINCREASES

URBAN CLIMATECHANGES

RUNOFFVOLUME

INCREASES

FLOWVELOCITY

INCREASES

PEAK RUNOFFRATE

INCREASES

LAG TIME &TIME BASE REDUCE

FLOOD CONTROL

PROBLEMS

CHANNEL SYSTEM (Conventional Mazhab)

POPULATION DENSITY

INCREASES

WATERBORNE WASTE

INCREASES

WATER DEMAND RISES

WATER RESOURCES PROBLEMS

GROUNDWATER RECHARGE REDUCE

STORMWATER QUALITY

DETERIORATES

BASEFLOW REDUCES

RECEIVING WATER QUALITY

DETERIORATES

POLLUTION CONTROL

PROBLEMS

RECHARGE WELL SYSTEM

(Pro Water Mazhab)

GROUNDWATER

CONTROL PROBLEMS

a. Conventional Mazhab Conventional Mazhab in drainage engineering is a drainage system which allow water flows to the trench, drainage canal, river and then to the sea. By this system the surface ground will have not inundation anymore but this system creates neglected water which ought to be a storage of groundwater. The consequence of this mazhab will cause increasing of peak hydrograph of flood in the downstream.

b. Pro Water MazhabBase of thinking, Sunjoto (1989):

When domestic water consumption 100 l/cpt/d, as average computation from urban domestic water consumption is 200 l/s/cpt/d and rural domestic water consumption is 60 l/cpt/d and the comparison of urban area is 30 % with rural area is 70 %.

Impervious area consumption is 30 m2/cpt (in the developed country?)

Data (real): Depth of precipitation 2,580 mm/y Evaporation-transpiration 1,250 mm/y Domestic water consumption 100

l/cpt/d Impervious area consumption 30

m2/cpt Coefficient of roof runoff 0.95 Population (model) 1,000,000 cpt a. Total domestic water consumption

Volume = 365 x 0.10 x 1,000,000 = 36.50,106 m3/y


b. Total neglected water

Volume = 0,95x30x(2.58-1.25)x1,000,000 = 37.90,106 m3/y

Volume of total neglected water as a result of conventional drainage system is equal to the volume of Total domestic water consumption.

4. Conventional Mazhaba. Inundation

Location Area Duration Frequency Depth Lost

b. Topography Direction of flow Hydraulic aspect Location of flow Direction of groundwater flow

c. Land use Building coverage ratio/BCR compare to Benefit

Cost Ratio Border of land Possession Value of assets

d. Soils Characteristic Strength


Permeability (SD)

e. Master plan/Regional space planning RTRW In accordance with planning

f. Infrastructure and utility Making use of existing structure

g. Demography Density in accordance with C = coefficient of

runoff

h. Institution Operation & Maintenance

i. Legal aspect Implementation in accordance with regulation

j. Community perception Participation of population

k. Social and economic aspect Class of construction

l. Sanitary Design aspect

m. Available material Choice of construction

n. Hydrology Time of concentration of precipitation Dominant duration of Precipitation

o. Cost Priority scale


Keyword: time of concentration


5. Mazhab Pro Water Benefit recharge system

1. Physical benefit

a. Decreasing of hydrograph peak> Retarding basin

b. Reduction of network dimension Dimension of drainage network can be

reduced Can be designed without drainage network

canal Public street can be enlarged

c. Prevention of local flood Low elevation ground surface have not enough slope to allow water flow, water should be infiltrated on the recharge well

d. Decreasing of waste concentration Due to fresh water increases ground water storage will increases to and concentration of waste water will decreases as formula:

(1)

For the region with brackish water, recharge well will be very useful to increase quality of water

e. To keep elevation of groundwater surface


1). To keep stable elevation of groundwater surface > Conversion from dense forest to housing

A c

b

Fig 3. Land conversion from forest to housing

2). Bring back to original position the elevation of groundwater surface > Conversion from critical land use to housing

c

a b

Fig 4. Land conversion from critical land use to housing

When recharge well is not implemented > bWhen recharge well is implemented > c

‘All build and improve the environment at once’f. Preventing of sea water intrusion


Badon Ghyben (1888) & Herzberg (1901) had developed water balance theory between fresh water and sea (saline) water in the circular sandy island as follows:

P r e c i p i t a t i o n

Ground surface Groundwater surface

h Sea level

hf hs

Fresh water (f) A Border of saline water

and fresh water Saline water (s)

Fig 5. Scheme of island cross section with homogeneous and isotropics soils

Point A laid in the surface border between sea water (s) and fresh water (f)

Hydrostatic head in point A is PA:

From point of view sea water:

(2)


From point of view fresh water:

(3)

Eqn (1) = (2) so:

>

> (4)

Usually, the characteristic of sea and fresh water are::

Sea water ρs = 1,025 t/m3

} -> (4) so ∆h = 1/40 hsFresh water ρf = 1,000 t/m3

The conclusion is when the elevation of groundwater decreases 1 unit as a result the border of sea water and fresh water below will go up 40 units, and on the contrary when the elevation of groundwater increases 1 unit as a result the border of sea water and fresh water below will go down 40 units

g. Preventing of land subsidence and sinkhole

The consequence of groundwater exploitation without equal conservation, water will disappear from void of soil and due to pressure of dead weight and soil will be compressed and land subsidence will occur.


h. Water conservation

Depth of precipitation = 2.58 m/yEvaporation-transpiration 40 % x 1.25=0.50 m/y (recharge system)Roof consumption = 30 m2/cptPopulation in year 2000 =128,450,000 cptWater consumption = 523,5 m3/cpt/y

Volume of water conserves by recharge system:

Vol = ( 2.58 – 0.50 ) m x 30 m2 x 70 % x 128,450,000 = 5,610,106 m3/th (5.61 B)Dependable flow for island of Jawa:

Without recharge system= 43,952 106 m3/th (see table)With recharge system = ( 43,952 + 5,610 ) ,106 m3/th

= 49,562 m3/thWater available = 49,562,106 / 128,450,000

= 385,85 m3/kpt/th.

Water balance = 523,5 / 385,85 x 100 % = 135,67 %

So the contribution of recharge system to decrease water deficit in the island of Jawa and Madura is:


152.98 – 135.68 = 17.30 %

Other technique should be implemented like forestation etc, to improve water balance in those islands.

Table 1. Available water in island of Jawa and Madura.

No Island LD CH ET CHE APT AM JP AT

- - m2 m/y m/y m/y m3/y m3/y cpt m3/cpt/y

0 1 2 3 4 5 6 7 8 9

- - - - - 3-4 2x5 25-35%

x 6 - 7:8

1 Jawa &Madura (1985)

132.187

x1062,58 1,25 1,33 175.809

x10643.952

x10691,269

x106 481,57

2 Jawa &Madura(1993)

132.187

x1062,58 1,25 1,33 175.809

x10643.952

x106109,443

x106 401,30

3 Jawa &Madura(2000)

132.187

x1062,58 1,25 1,33 175.809

x10643.952

x106128,292

x106 342,2

Source: Direktorat Bina Program Pengairan Departemen Pekerjaan Umum (1984)

2. Social and cultural aspect

a. Perpetuation of traditional technique

b. Principle developing of ’other’s prosperity’

c. Preventing social unrest

1). Flooding in downstream areaHand-out of Drainage Engineering Lecture, Departement of Civil Engineering and Environment, Gadjah Mada University 13/37

2). Housing yard without outlet

3). Increasing of social confidence

Dimension of Recharge Well

1). Department of Public Work (1990)

a). Well with pervious wall

Volume of water flow to the well Vol i = A I TVolume of water out through base Vol od = As T KVolume of water out through pervious wall Volos = P H T KStorage volume = As HWater balance on the well will be:

So:

(5)


b). Well with impervious wallWhen the wall of well is impervious, volume of

water out through pervious wall equal to nil (P H T K = 0) and formula becomes:

(6)

where:H : depth of water on the well (m)I : precipitation intensity (m/h)A : area of roof (m2)As : cross section oh well (m2)P : perimeter of well (m)K : coefficient of permeability of soils (m/h)T : duration of precipitation (j)

2). ITB (1990)Follow the principle of V. Breen that angka

precipitation distribution is 90 % and principle of Horton that natural infiltration is 30 % to runoff HMTL-ITB developed formula:

(7)

where:H : depth of water on the well (m)A : area of roof (m2)d : well diameter (0,80 s/d 1,40 m)p : factor of percolation (mnt/cm)R24j : highest precipitation in 24 hours (mm/d)0,70: runoff should be infiltrated (Horton)


0,90: anka precipitation distribution (V. Breen)1/6 : conversion factor from 24 hours to 4 hours

(V. Breen)

Fig 6. Scheme of water balance on the ground surface

Dimension conversion of parametersa). Factor of percolation to Coefficient of permeability

(8)

These formula above means that to find p in mnt/cm, found from 0,60 divided by value of K in m/h.

b). Daily depth of precipitation to Intensity of precipitation

(1). MononobeI = {( R/24 )( 24/tc )2/3 (9)

where :R : highest precipitation in 24 hours (mm)tc : time travel (h)I : intensity of precipitation (mm/h)


Precipitation Evapotranspiration

Runoff

Infiltration

(2). Hasper (1951)

(a). When duration of precipitation < 2 hours

(10)

(b). When duration of precipitation 2 < T < 19 hours

R24j/ I = 0.06 ( T + 60 ) (11)

where:R24j : highest precipitation in 24 hours ( mm/d)I : intensity of precipitation (m3/s/km2)T : duration of precipitation (mnt)

Note:

(12)

This formula above means that to find I in m3/s/km2, found from 10,000 divided by 36 multiply by value of I in m/h

Due to formula Hasper was developed base on the research in Jakarta and Mononobe in Japan so formula of Hasper is more preferable for the implementation in Indonesia.


3). Sunjoto (1988)

a. To get coefficient of permeability.

Forchheimer (1930) had developed a field test to

find coefficient of permeability of soils by one bore

hole. Bore hole with casing was filled by water

instantly, and be measured the difference of height of

water in certain different period by the principle as

follows:

a. Outflow discharge equal to shape factor multiply

by coefficient of permeability multiply by depth

of water (Q = FKH).

b. Outflow discharge from the bore hole is equal to

cross section of casing multiply by thickness of

water on bore hole divided in certain period

(Q = As x H / T).


Fig 7. Scheme of water balance on bore hole

(13)

(14)

where: Qi : inflow discharge (Qi = 0)Qo : outflow dischargeAs : cross section area of casingH : depth of waterT : duration of flowF : shape factor of casingK : coefficient of permeability

and Eqn (13) = Eqn (14) so:


Note: ;

, when As = π R2 so:

(15)

where:

K : coefficient of permeability (m/s)R : radius of casing (m)F : shape factor (m) {F = 4R (Forchheimer, 1930)}t1 : starting time of measurement (s)t2 : final time of measurement (s)h1 : starting water depth of measurement (m)h2 : final water depth of measurement (m)

b. Depth of water on wellSunjoto (1988) had developed formula

analytically by the principle:


1). Inflow discharge to the well is constant and different to nil. This assumption is in accordance with real condition is that as long as duration of precipitation will create the discharge flow to the well from a roof.

2). Outflow discharge from the well equal to shape factor of well multiplies by permeability of soil and depth of water on the well (Forhheimer, 1930, and Q = FKH)

.

Fig 8. Scheme of water balance on recharge well

3). Formula development

Those two above Sunjoto’s principles can be written as follows:


(16)

(17)

Where:As : is cross section area of wellVolt : volume of storageh : depth of watert : duration of flowQ : inflow dischargeQo : outflow dischargeF : shape factor of wellK : coefficient of permeability

and equation Eqn (16) = Eqn (17) so:

Solution by integration and when :

Note: ; so:

When t2 - t1 = T so:

Note: Hand-out of Drainage Engineering Lecture, Departement of Civil Engineering and Environment, Gadjah Mada University 22/37

The beginning of flow when t1 = 0 and h1 = 0 , and can

be written t2-t1 = T and h2-h1= H so the equation

becomes:

Note:

when As = π R2 so:

(18)

dengan:H : depth of water (m)F : shape factor of well (m)K : coefficient of permeability (m/h)T : dominant duration of precipitation (h)R : radius of well (m)Q : inflow discharge (m3/h) C : coefficient of roof runoff (-)I : intensity of precipitation (m/h)A : roof area (m2)


Inflow discharge from the roof or other impervious layer can be computed by Rational Method and Q = C I ADraw: Relationship between H and T, with another parameters are constant

Parameter of formula: Coefficient of roof runoff Intensity of precipitation Area of roof Precipitation dominant duration Shape factor of well (F)

The value of shape factor was developed for the first time by Forchheimer (1930) when he try to find the value of coefficient of permeability of soils whit field test by one bore hole (Usually the test carried out by two holes like Theme etc.)

Then Forchheimer was followed by other researchers:

(1). With formulation method:Samsioe (1931), Harza (1935) , Dachler (1936), Taylor (1948), Hvorslev (1951), Aravin (1965), Sunjoto (1989 -2002).

(2). With graphical method:Luthian J.N., Kirkham D. (1949), Hvorslev (1951), Smiles & Youngs (1965), Wilkinson W.B. (1968), Raymond G.P., Azzouz M.M. (1969), Al-Dhahir & Morgenstern (1969), Olson & Daniel (1981)


Fig 9. Curve of shape factor of well by some researcher


Table 2. Shape factor of well

No Condition Shape factor of well (F) References

F whenR = 1;L = 0;H = 0

1

Sunjoto (1989) 0

2a

4 π RSamsioe (1931)Dachler (1936)Aravin (1965)

12,566

2b18 R Sunjoto (2002) 18,000

3a

2 π RSamsioe (1931)Dachler (1936)Aravin (1965)

6,283

3b

4 R

Forchheimer (1930)

Dachler (1936)Aravin (1965)

4,000

4a

π2 R Sunjoto (2002) 9,870

4b5.5 R

Harza (1935)Taylor (1948)

Hvorslev (1951)5,500

4b2 π R Sunjoto (2002) 6,283


5aSunjoto (2002) 6,227

5bDachler (1936) 0/0

5b

Sunjoto (2002) 3,964

6a

Sunjoto (2002) 9,870

6bDachler (1936) 0/0

6b

Sunjoto (2002) 6,283

7a

Sunjoto (2002) 13,392

7b

Sunjoto (2002) 8,525


Table 3. Comparison of condition 3b and 5b.

3b

4 R

Forchheimer (1930)

Dachler (1936)Aravin (1965)

4,000

5b Dachler (1936) 0/0

5b Sunjoto (2002) 3,964

Table 4. Comparison of condition 4b and 6b.

4b5.5 R

Harza (1935)Taylor (1948)

Hvorslev (1951)5,500

4b

2 π R Sunjoto (2002) 6,283

6b Dachler (1936) 0/0

6b

Sunjoto (2002) 6,283

Table 5. Value of well shape factor in relationship between ‘ratio of pervious wall length to radius of well’, in condition 5b.Hand-out of Drainage Engineering Lecture, Departement of Civil Engineering and Environment, Gadjah Mada University 28/37

DACHLER (1936) SUNJOTO (2002)

LR

∆F%

0 0/0 3,964 ?0,00000

1

6,283 3,964 -

36,9090,0001 6,283 3,965 -

36,8930,001 6,283 3,969 -

36,8290,01 6,283 4,009 -

36,1920,5 6,529 5,830 -

10,7060,964 7,079 7,079 0

1 7,129 7,165 0.504

5 13,586 14,348 5,608

10 20,956 21,720 3,645

25 40,149 40,853 1,753

50 68,217 68,867 0,952

100 118,588 119,186 0,504

1000 826,637 827,101 0,056

10000 6.344,417 6.344,793 0,005

100000

0

433.064,548 433.064,818 0,0000

6Note: This values are computed when L = variable and R = 1.

Table 6. Value of well shape factor in relationship between ‘ratio of pervious wall length to radius of well’, in condition 6b.

DACHLER (1936) SUNJOTO (2002)


LR

∆ F%

0 0/0 6,283 ?

0,0000

01

12,566 6,283 -

50,0000,0001 12,566 6,284 -

49,9920,001 12,566 6,290 -

49,9440,01 12,566 6,351 -

48,0260,5 12,695 9,092 -

28,3811 13,057 11,054 -

15,3402,713 15,323 15,323 0

5 19,072 19,618 2,862

10 27,171 27,915 2,738

25 48,775 49,525 1,537

50 80,298 81,001 0,867

100 136,435 137,084 0,475

1000 909,584 910,083 0,054

10000 6.821,882 6.822,281 0,005

100000

0

454.792,118 454.792,400 0,0000

6Note: This values are computed when L = variable and R = 1.


Roof with gutter

Roof without gutter

Fig 10. Scheme figure of recharge well5. Infiltration water on the canal


Water losses : consist of evaporation and infiltration.

Infiltration on the canal inflicts a loss upon point of view of irrigation engineering but a benefit from point of view water resources conservation engineering.

Volume of infiltration of canal can be found by:

a. Direct measurement of drawdown in certain period on the section of canal which be closed up in the upstream and downstream.

b. Real time measurement of different discharge on the two sections of canal.

c. Computed by formulas: Moritz (1913) > empirical method Bouwer (1956) > semi graphical

method Sunjoto (2007) > analytical method

1). Moritz (1913)

Moritz formula (1913) is a semi empirical method which water losses depend on layer of the canal, discharge, velocity of flow, depth of canal, base width and slope of canal. All of data can be measured


in the field directly except the layer of canal can be found from Table 7., and the equation as follows:

(19)

where:

S : water losses in the canal (m3/s/km)C : daily water losses (m/day) Table 2.Q : discharge of canal (m3/s)V : flow velocity (m/s)N : ratio between base width to depth of waterZ : slope of bank (Z = h when v = 1)

Table 7. Value of C for the base layer of canal (Moritz, 1913)Soils C (m/d)

1.2.3.4.5.6.7.8.

ConcreteCement gravel with hardpan sandy loamClay and clay loamSandy loamVolcanic ashVolcanic ash and fine sandVolcanic ash, sand and clay

0.020.100.120.200.210.300.370.51


9. Sand and gravelSand loam with gravel

0.67

2. Bouwer (1965)Bouwer had developed formula and graph which

was derived empirically by the test of analog electric in the three conditions to compute volume of water losses by infiltration for the each meter of length of canal.

q = (Is / K). k . Ws (20)

where : q : water losses (m3/m/h)Is/K : value from the graph (Figure 2)k : coefficient of permeability of soil (m/h) Ws : width of water surface (m)


Fig 11. The three conditions of flow (Bouwer, 1965)

Fig 12. Value of Is/K (Bouwer, 1965)3. Sunjoto (2007)a. Canal with pervious layer or natural soil


(21)

Ws

Hw

Wb

Fig 13. Scheme of canal cross section with pervious layer

b. Canal with side linning

(22)

Hw

Wb

Fig 14. Scheme of canal cross section with linningwhere:q : water losses (m3/s/m)Hw : depth of canal (m)K : coefficient of permeability of soil (m/s)


Wb : width of base canal (m)Ws : width of water surface (m)
