Contents preface (VII) introduction 1—37

Partition
wall

Pier
Bed
Stream’s
wing wall
Service road
Transition
1 in 3

Y
Canal

bed

Side wall

Y
X X

Roadway	BedblockH.F.L.Streambed
	12:1

Z F.S.L.

Stream bed

Sectionat-YY

Top of wing wall

				Water stop-cum-	Top of wing	Section - XX
	Top of	Roadway	expansion joint
	wall
		railing		slab	Top of	D/S bed
Top of dowel		D/S F.S.L.	level
					side wall
	U/S bed level
Transition				H.F.L.	Bed		Transition ends
Bearing	Stream	bed	block
begins
				Abutment

Section at - ZZ
Fig. 11.2 Typical plan and section of an aqueduct (1)
Siphon aqueduct (Fig. 11.3) is an aqueduct in which the bed of the stream is depressed when it passes under the canal trough, and the stream water flows under pressure below the canal. In such aqueducts, the stream bed is usually provided with a concrete or masonry floor.

Road	Full supply level
HFL	Canal bed
U/S Stream bed	Flow	D/S Stream bed
Floor

Cutoff

Fig. 11.3 Siphon aqueduct

380 IRRIGATION AND WATER RESOURCES ENGINEERING
Aqueducts and siphon aqueducts are further classified into the following types:
Type I: In this type of structure, the earthen canal banks are carried as such and, hence, the culvert length (i.e., the length of barrels through which the stream water is passed under the canal) has to be long enough to support the water section as well as the earthen banks of the canal [Fig. 11.4 (a)]. In this type of structure, the canal section is not flumed and remains unaltered. Hence, the width (across the canal) of the structure is maximum. This type of structure, obviously, saves on canal wings and banks connections and is justified only for small streams so that the length (along the canal) of the structure is small. An extreme example of such a structure would be when the stream is carried by means of a pipe laid under the bed of the canal.

1.5:1

X
2x

Flow

Stream

pitching

Stone

Slope 1.5:1

Inspection road

Normal bed	HFL
level

Flow

3x

Stone pitching

Canal bed width	Cement
Top plan of aqueduct	concrete
	blocks
	Canal
Dowel	R.C.C. Barrel
F.S.L.		Bank level
Earth filling		HFL
Stream

1.5:1

X

1.5:1

Normal bed level

Stone pitching	Width of siphon aqueduct	Stone pitching
		Cement concrete
	R.C.C. Barrel	Lean
Inverted filter	blocks over inverted filter
		concrete

Fig. 11.4 (a) Typical plan and section of a siphon aqueduct (Type I) (1)
Type II: This type of structure is similar to the Type I with a provision of retaining walls to retain the outer slopes of the earthen canal banks [Fig. 11.4 (b)]. This reduces the length of the culvert. This type of construction can be considered suitable for streams of intermediate size.
Type III: In this type of structure, the earthen canal banks are discontinued through the aqueduct and the canal water is carried in a trough which may be of either masonry or concrete [Fig. 11.4 (c)]. The earthen canal banks are connected to the respective trough walls on their sides by means of wing walls. The width of the canal is also reduced over the crossing. In this

CROSS-DRAINAGE STRUCTURES

381

type of structure, the width of the structure is minimum and, hence, the structure is suitable for large streams requiring considerable length of aqueduct between the abutments.

	Inspection road	Berm	Brick masonry in
			cement mortar
	Canal
		FSL
HFL	Earth filling		Bank level	Normal
	bed
Level
					level
		Stream
Stone pitching	Width of siphon aqueduct			Inverted filter
		Lean concrete	R.C.C. Barrel
Cement concrete
blocks over
inverted filter
Fig. 11.4 (b) Typical section of a siphon aqueduct (Type II) (1)
		Wearing coat
		Road way
	FSL		R.C.C.
	Fillets	Fillets	Bearing
HFL		Bed block
	1
	12
Stream bed	Pier

Lean concrete
Fig. 11.4 (c) Typical section of an aqueduct (Type III) (1)