DROP - Hydraulic analysis and design of energy-dissipating structures
The Design Manual and Software Package - DROP - aim to help designers select and detail appropriate structures in low head applications where the drop may be up to 5m. The package supports the design of structures for dissipating energy on surface irrigation schemes and for locations below measuring wells and flumes on open channels in water supply and sewerage practice.
Background
In open channel irrigation schemes, particularly where the canal bedslope is 1% or greater, the cost of energy-dissipating structures can add significantly to the total cost of the conveyance and distribution system. The designer will therefore want to reduce, as far as possible, the number and unit cost of structures. However, it is important that the designer has a good understanding of underlying basic hydraulics so that the structure chosen is appropriate to the prevailing hydraulic conditions.

The package
The manual and the program were developed together and are structured in a similar way. However, the manual may be used independently of the software. The first part of each is devoted to the hydraulics of energy dissipation. Following this the package presents a range of standard structures drawn from world practice.

What it covers
- Hydraulics of energy dissipating structures
The ways in which various different types of structure dissipate energy are analysed. Principal hydraulic parameters such as specific energy, momentum, critical depth, Froude number and the characteristics of hydraulic jumps are presented.

- Energy dissipating structures: standard designs
Selected ‘type designs’ and a flow chart are presented to assist designers in the selection of a design, taking account of factors such as:

  • Ease of construction & the availability of construction materials
  • Performance in systems carrying sediment, debris or weeds

     

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  • Ability to perform other functions such as bridging
  • Possible health hazards arising from ponded water

    The software program
    The program is structured to allow users to undertake various related tasks. The design software runs under DOS but uses pull-down menus and push buttons. In modern PCs running later versions of the Windows operating system, memory management may need to be manually adjusted to permit the program to run.

    Within the program there is an on-line technical help facility. General help relating to the user interface and scope of the program is available from the main help menu. A brief program manual is included as an appendix of the design manual.

    Contributors
    HR Wallingford Ltd, UK

    Intended users
    The DROP Design Manual and Software are aimed at structural designers. The focus is on the hydraulic aspects of design. Once the user has obtained a satisfactory outline design according to defined hydraulic conditions, it is expected that the design of structural elements will proceed according to standard practice for structures exposed to water.

    Skutsch, J, 1997. Minor irrigation design, DROP - design manual. (Supporting software is optional) HR Wallingford, UK. Report no. OD/TN 86.

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    • Available at: http://www.dfid-kar-water.net/w5outputs.html
    For a CD ROM or a hard copy contact:
    International Development Group, HR Wallingford Ltd, Howbery Park, Oxon, OX10 8BA, UK
    Tel: +44 (0) 1491 835381, Fax: +44 (0) 1491 826352, E-mail: w5outputs@hrwallingford.co.uk