Rainwater harvesting/Surface water/Tyrolean weir

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Tyrolean weir icon.png
Small weir on River Gade, Watford - geograph.org.uk - 464777.jpg

A Tyrolean weir is a water inlet structure in which water is abstracted from the main flow through a screen over a gutter. The gutter is usually made of concrete and built into the river bed. The screen on the crest should slope downstream (15-30 degrees), to increase flow velocities and prevent sediment carried by the stream from blocking it. From the gutter, water enters a pipeline, which drains into a sedimentation tank and then flows by gravity into the rest of the system.

Dams and water inlet structures in embankments are vulnerable and expensive elements in river-fed water systems. They are easily damaged by floods, underflow, seepage and suffer from build-up of sediment or rubbish in the water. The Tyrolean weir forms a more reliable and cheaper alternative.

Suitable conditions[edit]

Tyrolean intakes are used in small permanent rivers and streams where the sediment content and bed load transport are low, or on the crest of a dam spill.

The weir or intake should be carefully sited.

The weir itself does not clean or purify the water.


Advantages Disadvantages
- More reliable and cheaper compared to dams and water inlet structures in river embankments

- They do not affect water flow to communities downstream

- None known


Resilience to changes in the environment[edit]

Drought effects on cement[edit]

Effects of drought: Badly made concrete or cracked linings (e.g. in tanks, dams, waterways, wells, and other structures).
Underlying causes of effects: Less water used for curing; Impure water used for mixing.
To increase resiliency of WASH system: Ensure adequate mixing, ratios, purity of ingredients; Minimize water content in mixture; Ensure adequate curing.


More information on managing drought: Resilient WASH systems in drought-prone areas.

Construction, operations and maintenance[edit]

A Tyrolean weir can either consist of parallel rods or a perforated plate, installed in the flow direction over the width of the stream with a 15-30 degree downward slope. Large stones, branches and large leaves cannot pass between the rods, and are prevented from entering the gutter. Because the rods / plate slopes downward, the material in the stream is pushed downstream, until it drops over the end of the weir.

The threshold can be a concrete elevation above the rocky bed of a mountain stream, or a vertical low weir structure, anchored in the embankment. The capacity of the inlet pipe / drain (diameter and gradient) should be 30% more than the design flow and have an uniform gradient to prevent accumulation of sand. The sedimentation tank can accumulate 1.5-2 m3 of deposits and allows water to filter for 10 to 30 minutes at very low speed. It is cleaned by washing it out.

Maintenance[edit]

Several visits per year to the site are necessary for inspection, cleaning and minor repairs. Overall, maintenance is easy to carry out due to low-tech structure and the use of local labour and materials.

Regular inspection and cleaning of the grit / rack and possibly the gutter and sedimentation tank is required during and after storm periods.

Costs[edit]

  • Material (excluding the pipe and sedimentation tank): US$ 300 - 600.
  • Labour (if site is easily accessible): 30 - 50 man days.

Manuals, videos and links[edit]

Acknowledgements[edit]