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[[Image:Tyrolean_weir_icon.png|right|80px]][[Image:Tyrolean weir.JPG|thumb|right|200px|Tyrolean weir|Man checking the grid at a Tyrolean Weir. Tanzania. Photo: D. Bourman, Aqua for All.]] 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 ===
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 itself does not clean or purify the water.
{| border="1" cellpadding="5" cellspacing="0" align="center"
|-
! width="50%" style="background:#efefef;" | Advantages
! style="background:#ffdeadf0f8ff;" | Disadvantages
|-
| valign="top" | - More reliable and cheaper compared to dams and water inlet structures in river embankments <br>
- They do not affect water flow to communities downstream| valign="top" | - None known
|}
===Resilience to changes in the environment===
====Drought effects on cement====
More information on managing drought: [[Resilient WASH systems in drought-prone areas]].
===Construction, operations and maintenance===[[Image:Tyro weir.jpg|thumb|right|200px|Tyrolian weirs are meant to intake water from mountain rivers that are very turbulent. Photo: [http://www.tuwien.ac.at/en/tuwien_home/ Vienna University of Technology]]]
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.
Regular inspection and cleaning of the grit / rack and possibly the gutter and sedimentation tank is required during and after storm periods.
===Costs===
* Material (excluding the pipe and sedimentation tank): US$ 300 - 600.
* Labour (if site is easily accessible): 30 - 50 man days.
==Field experiences== ==Reference manualsManuals, videos, and links===* [http://www.samsamwater.com/library/TP40_11_Surface_water.pdf Surface water intake and small dams]. Chapter 11. Revised by Nhamo Masanganise.
===Acknowledgements===* CARE Nederland, ''Desk Study : [[Resilient WASH systems in drought -prone areas]].'' October 2010.