See the following as a sample of what should be available. I think the half circle and other odd shapes have some possibilities. The corrugated curved sheets have the advantage of portability.
Drainage System that's easy to install, resistant to damage and durable enough to last for years. They're available in both aluminum and galvanized steel to suit any requirements. Diameters up to 3.6m (12 ft) and lengths up to 12m (39 ft).
Corrugated Steel Pipe was first developed and used for culverts in 1896. As experience was gained in the use of this thin-wall light weight, shop-fabricated pipe, the diameters gradually increased to 2.4m and larger. Fill heights became greater, even exceeding 30m. A further development, in 1931, was structural plate pipe with larger corrugations, for field assembly. Diameters and arch spans beyond 8m (25 ft) have been installed. Steel plate structures were complimented in 1962 by the addition of Corrugated Aluminum Plate Structures, introduced to the USA by Kaiser Aluminum with many thousands of successful structures now in service.
Offered by Mike.