23.1 INTRODUCTION

HYDRA is a storm drain and sanitary sewer analysis and design program. Originally designed and developed in 1975, the HYDRA program ran on mainframe computer systems. The objective of the HYDRA program was to provide hydraulic design engineers with a means of accurately, easily and quickly designing and analyzing storm, sanitary or combined collection systems. HYDRA achieved these objectives with a high degree of success, and for this reason, it was selected for incorporation into the HYDRAIN system which is supported by the Federal Highway Administration and 31 State Transportation Departments. Furthermore, if it is being used within HYDRAIN, there are those advantages associated with HYDRA s ability to interact with other related hydraulic design programs.

In the HYDRA design process, the program will select pipe size, slope and invert elevations if given certain design criteria. Additionally, HYDRA will perform analyses on an existing system of pipes (and/or ditches). When an existing system of pipes is overloaded, HYDRA will indicate suggested flow removal quantities as well as an increased pipe size as an alternative remedy. Additionally, HYDRA can optionally consider the possibility of surcharged systems. The design procedure is not optimized, so alternatives should be examined.

HYDRA requires the creation of an input file, consisting of commands to describe the drainage system. The commands are placed in a logical sequence, usually from higher to lower elevations. It is possible that several command sequences can produce the same result. The...