Combined Innovative Spillways: associating Concrete fuse plugs with PK Weirs increases by 60 % the capacity of the spillway Piano Key Weir and by 300 % the discharge of a Creager sill

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Lempérière & J.-P. Vigny (Hydrocoop – France) – June 2015

1. Combined Innovative Spillways associate Piano Keys Weirs and fuse plugs, allowing to benefit from the specific advantages of the two devices: those of the PK Weirs for the usual floods and those of the fuse plugs for the exceptional floods.

In comparison with a spillway including only Piano Keys Weirs, Combined Innovative Spillways make it possible:

– either to increase by 60% the maximum discharge without modifying the spillway length or the nappe depth,

– or to reduce by 40% the spillway length without modifying the discharge or the nappe depth,

– or to reduce by 1/3 the nappe depth without changing the spillway length or the discharge.

2. The here-below drawings present the general arrangement of the Combined Innovative Spillways. The figures are for examples below.

3. Two examples are here below presented for a spillway 50 m long associating concrete fuse plugs 3 m high with Piano Keys Weirs elements 3 m high with maximum walls height Pm = 2 m.

The first one includes 2/3 of the length of Piano Keys Weirs for 1/3 for fuse plugs which have all tilted for a nappe depth lower than 1 m. The table here below shows the order of magnitude of the corresponding maximum discharges to be compared with those of a spillway of same characteristics but including either 100 % of Piano Key Weir or a Creager wear.

Before tilting of the first plug, a nappe 0.85 m depth allows to discharge about 200 m3/sec, i.e. 40 % of the maximum discharge, percentage which represent for instance the 100 years flood.

Discharge for a 50 m length and 1 m nappe depth

2/3 PKW and 1/3 Plugs490 m3/sec
100 % PKW300 m3/sec
Creager100 m3/sec

The second one includes 1/3 of the length of PK Weirs for 2/3 for fuse plugs which have all tilted for a nappe depth h = 2 m. The corresponding discharges are indicated in the table here below.

Before tilting of the first plug, a nappe 1.70 m depth allows to discharge about 330 m3/sec., i.e. 1/3 of the maximum discharge.

Discharge for a 50 m length and 2 m nappe depth

1/3 PKW and 2/3 Plugs1000 m3/sec
100 % PKW610 m3/sec
Creager300 m3/sec

It appears that the increase versus a solution 100% Piano Key Weir is about 60%.

4. Similar results could be obtained using Fusegates or flap gates instead of fuseplugs.

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