The design phase consisted mostly of hydrological modeling and re-modeling, trying to optimize capacity of the culverts while minimizing the cost of installation. The crucial number that the team was trying to optimize was the invert elevation of the culverts. Our objective was to minimize the amount of excavation needed to make grade for the culvert installation.
In the end, the hydro analysis showed that six culverts, 1m in diameter, with a slope of 2%, would provide enough capacity to act as the additional emergency spillways for the reservior. To determine the invert elevation for the culverts, we checked many different scenarios in the stage/storage model for the reservior. The few scenarios that met all necessary hydrological criteria were compared with the existing site elevations, and a final decision was made in line with the original objective of minimizing excavation.
The structural details were determined for the sub-base stone layer, concrete collar wall (to aid in preventing water seepage along the length of the culverts), and backfill. Design sketches were sent over to Cambodia in the beginning of March, and construction promptly started. Readily available pre-cast concrete culvert sections, 1m in length, are the typical materials used for culvert installation throughout this region of Cambodia. In the above photo, sections of culvert are being set, and the concrete collar wall has been cast, visible in the background.