Cross drainage works is a much heard term. However, it is not always clear as to what cross drainage works actually mean. The term stands for the structures carrying all the discharge from any natural stream across a canal system that intercepts the former. Canal systems are present along water bodies such as rivers, lakes, large drains and even other canals. Canals are almost like an obstruction.
Therefore, the structural intercepts made for carrying canal water across the water bodies or obstructive systems are actually called cross drainage works. This is not very easy to make and must always be avoided to be built in ways to divert a stream into other streams or even for altering canal alignments so as to make it cross stream junctions.
As per the discharge and levels involved, there are several types of cross drainage works. The two basic categories are the aqueduct and the siphon aqueduct. In the former category, the drain HFL is located below the bottom of a canal system in a way that water of drainage freely flows under gravity. This is an aqueduct setup.
The water of the canal gets carried across the drainage via a pier supported trough. This is also located in bridges that carry water. An aqueduct setup is conducive when there is a good enough water level difference in the natural water and canal water. The bed of the canal will need to be higher perched than the HFL.
Siphon Aqueducts
In this category, the drain HFL is higher than the canal bed, by a good margin. The water actually runs through the barrels under the siphonic action. The bed of the drain is depressed and comes with pucca floors at the upstream ends. The bed for drainage might be joined up to the pucca floors using vertical drops or via a 3:1 glacis.
The rising slope must have a steepness in the ratio slope: steepness 5:1. While the canal passes over drains, cabal structures stays open and therefore, it is hard to see this structure receiving flood damage. However, when there is heavy flooding, the main foundation is highly susceptible to jamming or scouring via debris and accumulated material.
Another aspect to be taken care of here is that there is an acute need for maintenance. There has to be professional maintaining from time to time since the areas of access are limited. Moreover, you need to understand that only professional setups come handy here. Most of these aqueducts are commercial structures and thus, this isn’t a concern at all.
Hydraulic Setups
Another kind in this category of cross drainage works is that of a hydraulic setup. In this type, the drainage that passes over irrigation canals is defined as super passage. The setup is perfect for cases wherein the drainage bed level is above flood levels of the canal surface. The canal water clearly passes below the area of drainage.
The super passages are like aqueducts except for the context of the drain being over the existing canal structure.
Cross drainage works are huge commercial applications because depending on these water bodies and canals are set up. While it isn’t a visible structure very often, sites of canals definitely have these setups. Timely maintenance will keep the value of the cross drainage work intact while also keeping it well maintained.
The better the condition of cross drainage, the smoother is the operations. The best laid cross drainage structures last for years and hardly cause any concern except for regular clean ups. Companies involved in such works have been in the business for ages and can be trusted fully to lay down the best foundations for the drainage works.
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