STILLING BASIN DESIGN OF COMBINED

INLET-OUTLET STRUCTURES FOR

FLOOD CONTROL AREAS WITH

CONTROLLED REDUCED TIDE

Vercruysse, J.; Verelst, K.;

5-10-2015

Belgian Hydraulics Day

Outline

• Introduction

• FCA-CRT

• Combined in- and outlet structure

• Scale model

• Results

• Stilling basin without end sill

• Locally deepened stilling basin

• Locally deepened stilling basin with baffle

blocks

• Conclusion

• Questions

Introduction

FCA-CRT

Within framework Sigmaplan Flood Control Areas (FCA) are setup in

polders along the tidal section of the river Scheldt and its tributaries

In some of these FCAs a Controlled Reduced Tide (CRT) is

introduced

3

Introduction

Combined in- and outlet sluice

• FCA-CRTs Lippenbroek, KBR: seperate inlet and

outlet structure

• Recent FCA-CRTs: Combined in- and outlet structure

• Cost and ecological benefits

• Design FCA-CRTs: subcontracted to consultants

• W&Z assigned FHR to do a hydraulic revision

River FCA-CRT

Scale model

• Scale1:8

• Adjustable:

• Bergenmeersen, de Bunt, Vlassenbroek I, Grote Vijver I,

Zennegat,…

• Simplifications:

• 2DV model vertical plane along axis of flow

• Width model = 1,5 x culvert width

• Only inflow is studied

5

FCA-CRT river

Scale model

Glass wall

Model section

Width = 0.56m

Height = 1.0m

Length = 12.1m

Aeration Y/N Adjustable

Floor level / stilling basin / end sill

Adjustable

lenght, height

and location

6 check valve

stop logs

• Design of stilling basin

Results

Standard stilling basin design:

• Upstream: design level

• Downstream: conjugated

water depth

FCA-CRT stilling basin design:

• Upstream: tidal river

• Downstream: increasing water

level during filling of the FCA-CRT

Predicted FCA - CRTlevel in

function of river level:

Results

Stilling basin without end sill

• Vlassenbroek – Geometry nr. 2:

• Drop height 4.10 m.

• Concrete ends at 15 m downstream of the drop.

Results

Stilling basin without end sill

9

OK NOT OK

(max range

velocity sensor

= 7 m/s)

conjugated water depth <-> predicted CRT levels

conjugated water level higher then predicted levels

supercritical flow conditions at CRT side

good agreement with formula Rand and Chanson.

Benodigd corresponderend polderpeil >= min polderpeil

Results

Stilling basin without end sill

10

Results

Locally deepened stilling basin

• Locally deepened stilling basin with end sill

Results

Locally deepened stilling basin

• Conjugated water depth according to bottom level

locally deepened stilling basin.

• Reduction of near bottom velocity.

Stilling basin without end still

Localy deepened stilling basin

Results

Locally deepened stilling basin with

baffle blocks

• Locally deepened stilling basin with baffle blocks

Designed according to rules usbr type III stilling basin

Results

Locally deepened stilling basin with

baffle blocks

• Reduction of bottom near velocity at low FCA-CRT

levels

• Reduction of conjugated waterdepth

Without baffle blocks With baffle blocks

Conclusion

• Depth stilling basin according to literature formula.

• Higher FCA-CRT water levels ≠ lower velocity.

• Energy dissipation decrease when free hydraulic jump

transform to a drowned hydraulic jump.

• Ceiling is necessary to redirect falling nape with

increasing water levels in the FCA-CRT.

• Good results with baffle blocks designed according

rules usbr type III stilling basin.

Questions?

• Neglecting trash racks and columns

Questions?

• Advantages and disadvantages of baffle blocks

• Hydraulic

• Erosion of baffle blocks?

• Fish mortality?

Without baffle blocks

With baffle blocks