The concept of Minimum Energy Loss (MEL) weir was developed by late Professor G.R. McKAY. MEL weirs were designed specifically for situations where the river catchments are characterised by torrential rainfalls (during the wet summer) and by very small bed slope (So ~ 0.001). The design was developed to pass large floods with minimum energy loss, hence with minimum upstream flooding. The first MEL weir was the Clermont weir (QLD, Australia 1963) (Photo 7 to 13) (CHANSON 2003). The largest, Chinchilla weir (Qld, Australia 1973), is listed as a "large dam" by the International Commission on Large Dams (1984). A related design is the un-gated spillway inlet at Lake Kurwongbah (Sideling Creek dam). It was designed with the concept of minimum energy loss, in a fashion somehow similar to the design of minimum energy loss culvert inlet (McKAY 1971). The crest inlet fan converges into a 30.5 m wide channel ending with a small flip bucket. The MEL crest design allowed for an extra 0.457 m of possible water storage. Another MEL spillway inlet was designed at Swanbank dam (Fig. 5 & 6).

The purpose of a MEL weir is to minimise afflux and energy dissipation at design flow conditions (i.e. bank full), and to avoid bank erosion at the weir foot. The weir is curved in plan to converge the chute flow and the overflow spillway chute is relatively flat (Photo No. 1). Hence the downstream hydraulic jump is concentrated near the river centreline away from the banks and usually on (rather than downstream of) the chute toe. The inflow Froude number remains low and the rate of energy dissipation is small compared to a traditional weir. Ideally, a MEL weir could be designed to achieve critical flow conditions at any position along the chute and, hence, to prevent the occurrence of a hydraulic jump (CHANSON 1999, pp. 418-419). Practically this is not achievable because the variations of the tailwater flow conditions with discharge are always important. In practice, a weak jump takes place at the chute toe.

MEL weirs are typically earthfill structures protected by concrete slabs. Construction costs are minimum. A major inconvenient of a MEL weir design is the risk of overtopping during construction (e.g. Chinchilla weir). In addition, an efficient drainage system must be installed underneath the chute slabs.

A case study : Chinchilla MEL weir
The Chinchilla weir (QLD, Australia) is located on the Condamine river, part of the Murray-Darling basin (Photo No. 2). Completed in 1973 to provide irrigation water, the 14-m high weir is an earthfill overflow embankment with a 410-m crest length. The original volume of the reservoir was 9.78 E+6 m3 and the reservoir area is about 3.58 E+6 m2. The maximum spillway capacity is 850 m3/s and no dissipation structure was built. The overflow section is concrete-lined, with a series of drains to reduce seepage pressure. The right bank channel has a lower crest elevation to act as a low-flow channel. The Chinchilla weir was designed to give no afflux at design flow (850 m3/s, bank full). It passed a flow rate of 1,130 m3/s with a measured afflux of less than 100 mm in 1974 (TURNBULL and McKAY 1974).

During construction, the Chinchilla weir was overtopped, partly damaged and later completed as planned (TURNBULL and McKAY 1974) (1). Between 1973 and 2013, the weir was overtopped by a number of large flood events. The weir operated safely and properly, and inspections after the flood showed no damage (CHANSON and APELT 2022,2023).
 

Discussion
The Minimum Energy Loss weir is basically an overflow embankment. Other types of overflow embankment design include the earth dam spillway with precast concrete blocks (CHANSON 2001, pp. 225-230) and the concrete protection of the downstream embankment slope (Photo No. 4). The former is a Russian design developed by late Professor Gordienko while the latter has been used in North-America and Australia, with roller compacted concrete (RCC) or conventional concrete.

Footnote

Detailed photographs

Photo No. 2 : Chinchilla weir (Chinchilla QLD, Australia 1973) on 8 Nov. 1997 during low overflow. Designed with the assistance of Professor Gordon McKAY. Weir height: 14 m, Crest length: 410m, Spillway capacity: 850 m3/s, Condamine river. The Chinchilla weir is listed as a "large dam" by the International Commission on Large Dams (1984). More information : CHANSON, Butterworth-Heinemann, 1999, pp. 417-421 & 316.

Photo No. 3 : Lemontree weir (Cecil Plains QLD, Australia 1979) on 8 Nov. 1997. Minimum Energy Loss weir on the Condamine river. More information : CHANSON, Butterworth-Heinemann, 1999, pp. 417-421.

Photo No. 4 : An overflow embankment dam : Melton dam (VIC, Australia). Completed in 1916, the dam was heightened twice because of the rapid reservoir siltation. During the last refurbishment in 1994, the overflow stepped spillway was added. More information at {Embankment overflow stepped spillways: earth dam spillways with precast concrete blocks}.

Photo No. 5 and 6 : Swanbank Minimum Energy Loss spillway (Ipswich Qld, Australia 1965). Photo No. 5 : spillway inlet, view from the dam wall on 6 Sept. 2002; Photo No. 6 : spillway ogee, with the power station in background on 6 Sept. 2002. More about Swanbank power plant.

Photo No. 7 to 13 : Sandy Creek at Clermont QLD (Australia 1963): Photo No. 7 : Early stages of construction in 1962 (Courtesy of Mr Keith JAMES). Photo No. 8 : Downstream face near completion in early 1963 (Courtesy of Mr Keith JAMES). Photo No. 9 : Workers on the downstream face near completion in 1963 (Courtesy of Mr Keith JAMES). Photo No. 10 : view from the right bank on 3 Sept. 2002 (Courtesy of Mr Keith JAMES). Photo No. 11 : detail of the crest intake on 3 Sept. 2002 (Courtesy of Mr Keith JAMES). Photo No. 12 : Flood overflow on 8 March 1993 (Courtesy of Mr A.J. HOLMES). Photo No. 13 : Flood overflow in Feb. 1999 (Courtesy of Mr A.J. HOLMES).

Photo. No. 14 & 15 : Lake Kurwongbah dam (also called Sideling Creek dam). The dam is equipped with a Minimum Energy Loss spillway intake. Spilway operation on 22 May 2009 morning. Photo No.14: spillway intake with a very small overflow at 08:20. Photo No. 15: flip buicket operation; note the discharge confined to the low flow section.

References

Acknowledgments

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