Designing Drainage Systems


There are many factors which will affect the layout of the drain that ought to be considered.

In a traditional network, the small drainage system is generally a pipeline having adequate capacity to include the aggravation flows. All these pipelines avoid stormwater damage to properties and limit the frequency and amount of surface water to a degree acceptable. They are usually designed to accommodate for flows using a five-year average recurrence interval (ARI). The pipelines do not always stick to the natural drainage route and are often aligned along land boundaries as well as the roadways and canals and stormwater drain cleaning is often necessary.

The significant drainage system caters to runoff from storms generating higher peak flows compared to the small drainage system was designed. The significant drainage system is intended to manage overland flows resulting from storms using a 100-year ARI. Even a roadway, a drainage channel, a pipeline or a combo of the aforementioned may work as a sewer line. The final surface level of allotments adjoining to the overland flow route has to be at least 300mm above the 100-year ARI flood level.

Particular details like reverse fall front nature strips and low footpaths might have to be supplied at street low points to permit transverse flow of flood waters at which adjacent to drainage reserves. Footpaths should not be low-down if the stream is traveling longitudinally across the roadway.

Drain place

When designing drainage pipelines, the layout has to be expanded to cross any street or proposed road extending that is adjacent to the growth. This ensures any present or proposed solutions within the road reserves are understood and the drainage works might cross these solutions.

As well as normally adhering to normal watercourse alignment, drains need to be as functional to be made to accompany easements or reservations meant for drainage functions.

Easements and reservations have to be measured to cover the width of the drain in addition to provide for accessibility, maintenance and construction.

Construction and maintenance requirements are especially important factors when designing waterway functions. Relevant considerations include:

  • The maximum gradient and elevation of the grassed batters
  • Whether trucks need access to this channel reverse
  • Where inlets and streets are located
  • If there are constraints on the usage of specific construction methods (when adding to, or replicating existing drains in built-up regions for an example)
  • Ground conditions
  • The distances in the projected alignment to some present solutions (especially if any difficulties exist with unwanted effects throughout excavation)
  • The way overhead electricity lines are situated and also the width of roads

Positioning of an underground drain inside the sidewalk area of a street is acceptable if it is not appropriate to find the pipeline away from the sidewalk area.

Potential limits on using specific construction techniques will need to be taken into consideration when choosing a underground drain recovery. This is especially true when adding to duplicating existing drains in built-up places.

Surface Obstacles

Surface obstacles like buildings, power provider sticks, native plant or big trees, etc. can influence the planned orientation of the drain. This ought to be found during the first survey and review of the location. In case the proposed drain place cannot prevent or carefully approaches the obstruction, then it is going to be required to speak to the appropriate authority and tree removal service.

Current bridges or tunnels may also help determine the design. All these have to be assessed with tree arborists to make certain they’re effective at coping with the extra discharge in the proposed drain. The orientation and ability of the present structure might have to be enhanced during construction if needed.

Underground obstructions

Underground solutions having the capability to affect drainage layout include:

  • Underground electricity wires
  • Petroleum pipelines
  • Gas mains
  • Communication wires
  • Water heaters
  • Sewer mains
  • council drains
  • Traffic signal wires

An analysis ought to be undertaken to test for important services at 100m both upstream and downstream of the proposed functions. The thickness of a prospective drain might be affected by some or all of these services and by any construction foundations or comparable below-ground structures. Transforming the amount or location of a single part of a planned drain can avoid future expensive changes to significant services.

Water services or underground service locating services must be contacted for advice on their resources, such as dimensions, thickness and location. Site inspection and demonstrating excavations also needs to be utilised to spot and affirm possible underground obstacles.

When designing a drain to conduct parallel into a sewer, it is important to look at how this will impact residential connections. This aspect ought to be assessed early in the design phase to allow the most economical solution to be embraced.

The designer should consult with the Water Services Association of Australia Sewerage Code for advice.

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