2 Hydraulic Engineering for Nature - 2.2 Hydraulic Structures

Question 1

Hydraulic Engineering

Answer 1

 Maintain the hydraulic function of the river
– control of flood and low flow
– stability of the river bed

 Protect the aquatic ecosystems
– protect the self purification of waters
– protect and restore aquatic habitats within morphological structures of
the river

 Support recreation and tourism
– protect the landscape of flood plains and natural valleys
– bathing, walking, cycling, canoeing

 Support other water uses
– water utilities infrastructure
– …

Question 2

Longitudinal Profile – Some Principles

Answer 2

 Bottom (base) slope given by the slope of the valley and by the river course.

 Adequate bottom slope can be determined by comparison with a reference reach of the river (according to shape and stability, should be at least 0,3 ‰).

 In the low lands only marginal slope possible: large cross sections, intensified sedimentation.

 Exceeding critical values of sheer stress threatens stability of the river bed – measures for erosion protection:
– Lowering bottom slope by prolongation of the river course.
– Building steps (! ecological continuity).
– Widening of the cross section.
– Fastening of bed material (point shaped or continuous).
PD

Question 3

Transverse Profile – Some Principles

Answer 3

 Discharge water, bed load and ice without causing damage.

 Discharge low -> relatively high water depth (narrowing of profile).

 Discharge high -> relatively low water depth (widening of profile).

 Shear stress should not exceed critical values.

 Mind the maximum gradient of river bank.

 Changes in groundwater level -> !land use in the flood plain.

 Use local construction material and techniques.

 Preserve the aesthetics of the landscape.

 Preserve habitats of organisms.

 Consider economic aspects of maintenance of the structures
and water bodies.

Question 4

Maintenance of Rivers

See table on slide 21

Answer 4

Maintain cross-section for freemflow:
mowing, removing weeds, repairing damage

River maintenance can be integrated into landscape ecological management

River maintenance at the wrong time can cause serious damage for the environment

Question 5

Cross Section: Hydraulic Load and Vegetation

Answer 5

See picture on slide 22

Question 6

Stabilization of River Bed Profiles

See picture on slide 23 and 24

Answer 6

 Dead material: artificial or natural construction material (stones, concrete, metal, bitumen, plastic material, wood)

 Living organic material: planting of reed and soft wood

 Combination of materials: often required because reed becomes effective not before some vegetation periods passed

Question 7

Channel Bottom Structures are divided into

1. Steps and ramps
2. Sills

Definition of Channel Bottom Structure

Answer 7

structures for the protection from erosion, which are mainly placed at the bottom of the river.

Question 8

Channel Bottom Structures are divided into

1. Steps and ramps
2. Sills

Definition of Steps and ramps

Answer 8

get over a difference in innovation of the river bottom, was reduced slope upstream and maybe downstream of substructure. hydraulic effect on stream conditions as required to convert energy; do not allow accumulation of sediments (minimum slope), take care for ecological continuity.

Question 9

Channel Bottom Structures are divided into

1. Steps and ramps
2. Sills

Definition of Sills

Answer 9

usually extent over the whole width of the river, fixation of the bottom of the river but no change of the slope of the river bed, almost impossible to prevent erosion near the sill.

Question 10

Steps

See pict on slide 26

Answer 10

 Drop structures: vertical drop or steeply sloped bed surface (up to 1:3)

 Cascade drops: can be arranged as cascades with hydraulic interaction; hydraulic drop at first and last step

Question 11

Ramps

See pict on slide 27

Answer 11

 River bottom ramp: slope 1:3 to 1:10; rough surface material causes dissipation of energy

 River bottom slide: slope 1:10 to 1:30; rough surface, wide variety of designs

Question 12

Sills

See pict on slide 28

Answer 12

 Barrages: protrude from the river bed; hydraulic drop at crest (like weirs); reduces energy gradient in upstream water

 Ground sill: protrude only slightly ; normally no hydraulic drop or only at very low flow conditions, useful for small exceedance of critical slope

 River bottom sill: flush with river bed; local fixing of the bed

Question 13

Crossing structures definition

Answer 13

structures for crossing a bottle body (transportation routes,
water courses, dams, buildings)

Question 14

There are two type of Crossing structures

Answer 14

1. Culvert Structures (gorong-gorong)
Bridges
Crossovers
Culverts
Inverted siphons
Tubbing casing
Passage

2. Outfall structures
   Outlet structures
   Inlet structures
   Tidal outlets

Question 15

Culvert structures - Bridges

Answer 15

structures with own supporting structure for carrying traffic, over cross-section is usually reduced to not less than 60%, free board ca. 0,5 m at design flood, take care for the requirements of navigation if the river is navigable

Question 16

Culvert structures - Crossover

Answer 16

a water body or pipe crosses a water body; cross-section must be sufficient so water cannot pour over

Question 17

Culvert structures - Passage/ford (lorong)

Answer 17

crossing at or near bottom level of the river, only with low frequent traffic, if the road is elevated, there should be pipes with a diameter of ≥ DN 400 in order to avoid backwater, ramps should have lower slope than river bank

Question 18

Culvert structures - Inverted siphons

See pict on slide 31

Answer 18

– Water crosses with free surface

– narrowing of the cross profile by 40 to 60 %

– at flood conditions often backwater; no freeboard

– design: consider maintenance, retention and ecological continuity

Question 19

Culvert structures - Culverts

See pict on slide 32

Answer 19

– water crosses below a barrier (or another water course)

– under pressure; one or more pipes;

– flow velocity should be > 1 m·s-1 (not less than 0.30 m·s-1);

– casually cleaning resp. flushing required

Question 20

Outfall structures - Outlet/Inlet Structures

See pict on slide 33

Answer 20

 Withdrawal of cooling water etc.

 Discharge of storm water or waste water

 Construction of outlet/inlet structures often similar to bridges or culverts

 Design of the cross sectional area of the outlet/inlet based on design flow of the main river and the tributary

 Consider minimum remaining discharge in the river

Question 21

Outfall structures - Tidal gates/sluices

See pict on slide 34

Answer 21

– Outlets/inlets with a lock
– e.g. water passes a dyke
– e.g. control of discharge or water level in a tributary/canal etc.