REMODELING OF EXISTING SPILLWAYS (PART 3)


REMODELING OF EXISTING SPILLWAYS (PART 3) By R.M.Khatsuria

Hydrotopics

Remodeling for ensuring structural safety

 

A necessity for remodeling to ensure structural safety may arise because

 

  • the dam is pretty old and turns out to be structurally unsafe according to present practice
  • increased inflow/outflow discharge requires a wider section of the spillway
  • additional loads are introduced following a major earthquake

 

In the above cases, hydrologic and hydraulic safety considerations are also involved together with structural safety that generally requires strengthening of the dam cross section with buttresses and other similar measures. However, for spillway, widening of the cross section is the only alternative available. In addition to ensuring a good bond between the old and the new construction, such a modification would have serious implications on the hydraulics of the spillway and energy dissipating arrangements. Figure 1 depicts a possible remodeling of an existing spillway by way of flattening of the rear slope for widening of…

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REMODELING OF EXISTING SPILLWAYS (Part 2)


REMODELING OF EXISTING SPILLWAYS (Part 2) BY R.M.Khatsuria

Hydrotopics

 

(For similar topics refer http://hydrotopics.wordpress.com)

 

R.M.Khatsuria

(email: rmkhatsuria@rediffmail.com

 

 

 (Want to refer Part 1?)

Remodeling for the purpose of increasing the storage of the reservoir involves raising of the reservoir level above the normal operating level and this would result in additional submergence of land in the upstream. In the case of ungated spillways, the normal operating level is at the crest level and there always is a temporary submergence caused by the overflow depth during the passage of floods. Thus, the full reservoir level (FRL) can be raised up to the maximum depth of overflow corresponding to the allowable limit of the upstream submergence. However, with the gated spillways, the FRL is required to be raised, which brings additional area under the submergence, beyond that corresponding to the original FRL. Thus, the remodeling is to be accomplished under the above mentioned pre-requisites.

When…

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REMODELING OF EXISTING SPILLWAYS (Part 1)


REMODELING OF EXISTING SPILLWAYS (Part 1) BY R.M.Khatsuria

Hydrotopics

 

(For similar topics refer http://hydrotopics.wordpress.com)

 

R.M.Khatsuria

(email: rmkhatsuria@rediffmail.com)

 

Though, all the aspects concerning hydrology, geology, topography and operational needs are taken into account while designing a spillway, eventually some spillways of  existing dams require remodeling. This may be due to a variety of reasons. The most prominent are:

·         Safety of the dam- This may be hydrologic safety or structural safety

·         Need for increasing the storage capacity of the reservoir

·         Environmental consideration, i.e. reducing fish mortality during overflow 

·         Replacement of aging components such as gates 

The most compelling case is concerning the hydrologic safety of the dam. In the last decade, existing dams were specifically surveyed in various countries to assess their safety. One of the most comprehensive surveys was conducted by the Corps of Engineers of the US Army (USACE), which included more than 80,000 dams. It was revealed…

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