Tuesday, April 12, 2011

A Civil Engineering Wonder


Even before you enter the Tehri Hydropower Development Corporation (THDC) project site, it's clear that you're about to witness a grand spectacle. The length of the water before the dame is something like what we studied in Channel Hydraulics, except that the actual meaning of a 20 km long M2 profile is hard to understand on a blackboard.

In Fluid Mechanics, we learned that a dam has a trapezoidal cross section, except the rectangular part on top which opens up to the spillway. However, little did we think or proportions then: a top-width of just 20 m is dwarfed by a bottom width of 1,125 m - that's millions of cubic metres of clay and RCC. Now, since summer had just started and the Bhagirati never dries up anyway, we couldn't see the Head Raise Tunnels (HRTs), but at least we found out that they're drilled into the mountainside, which also houses the powerhouse (we weren't allowed to go there).

If that wasn't enough, the chute spillway is another grand creation that seems impossible for a human being and his machines to construct - yet it was done, and indigenously at that. The sight of a hydraulic jump being formed as the water leaves the powerhouse was sheer beauty for the trained eye of a civil engineer.

The engineers there were helpful, although they seemed to have forgotten technical terms. So, while we asked about the need for a concrete apron in case of supercritical flow being restored after the spillway in peak season, he seemed utterly perplexed at the mere thought of supercritical flow! Still, our professor was there to explain things to us.

A view of the Morning Glory Ungated Spillways (we thought they were just for decoration) and some extraordinary roads built on the side of a steep cliff, coupled with a game of skipping stones at the dam downstream, and it was time to eat!

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