INSPECTION OF SITE AND RECOMMENDED RULE SHOULD BE ELABORATED BEFORE SELECTION OF SITE FOR CULVERT OR A SMALL BRIDGE.

It is necessary to have inspection of the suitable site where a culvert or small bridge is a choice and the inspection should also include notes on the channel conditions from which the silt factor and the co-efficient of rugosity can be estimated, so required for the flood discharge. The best way to calculate maximum discharge from data collected by personal inspection of the existing structure is necessary including the local enquiry for useful information, namely, marks indicating the maximum flood level, the afflux, the tendency to scour, the probable maximum discharge, the likelihood of collection of brushwood during floods, and many other particulars. It should be seen whether the existing structure is too large or too small or whether it has other defects. All these should be carefully recorded on the data records of the selection of site preferred by the Engineer in charge. The following points should particularly be noticed where there is any choice of site :-- Which must be situated on a straight reach of the stream, sufficiently below the bends;(2) Which is so far away from the confluence of large tributaries as to be beyond their disturbing influence. (3) Which has well defined banks ;(4) Which makes approach roads feasible on the straight and (5) Which offers a square crossing as far as possible. In siting small bridges and culverts, due consideration should be given to the geometrics of the approach alignment and the latter should essentially govern the selection of the site unless there are any specific problems of the bridge design. The recommended rule required for the flood discharge can be estimated in three different ways and the values obtained should be compared. The highest of these values should be adopted as the design discharge provided it does not exceed the next highest discharge by more than fifty percent, If it does , restrict it to that limit. The necessity for this elaborate procedure for fixing discharge arises for sizeable structures and as regards the small culverts discharge may be taken as the discharge determined from the run -off formulae.

IT IS NECESSARY TO COLLECT SUFFICIENT DATA FROM THE CATCHMENT AREA AND RAINFALL, CONVEYANCE FACTOR AND SLOPE OF THE STREAM, AS EXPERIENCE HAS SHOWN THAT SOME TIMES SERIOUS MISTAKES ARE MADE THAT LEADS TO WASTE THROUGH UNSAFE AND UNECONOMICAL DESIGNS.

Road project detailed project reports are prepared for the five years plan of the required time for completion of the work to be executed by the department concerned or the agency, as the case may be, however sometimes based on insufficient data and this causes delay in completion as well as use ans exercise of the schemes for execution. While the speed in execution of the plan and proposal is essential, at the same time the quality of work is also required to be maintained as per the Detailed Project Report technically sanctioned by the Engineering department of the Agency. As for as the design of a culvert or a small bridge is concerned it is not a small thing /matter to be despised by the Engineers. It must be remembered that the number of culverts and the small bridges in any road project is so large that, together, they account for a considerable portion of the total expenditure. As for as experience related to the design &Scope of such culverts and the small bridges is concerned it is revealed that sometimes serious mistakes are made in these simple matters and that leads to waste through unsafe, uneconomical as well as the ignored facts of methods for calculating the flood discharge from the catchment area and rainfall, from the conveyance factor and slope of the river and required for the flood marks on existing structure outlined with the suggestion made for fixing the design discharge of the stream.