City of Morgan Hill Sewer System Master Plan 2017

August 2017

6-1

City of Morgan Hill

Sewer System Master Plan

2017

City of Morgan Hill

6.0

CHAPTER 6 - HYDRAULIC MODEL DEVELOPMENT

This chapter describes the development and calibration of the City’s

sewer system hydraulic

model. Hydraulic network analysis has become an effectively powerful tool in all aspects of

sanitary sewer system planning, design, operation, management, and system reliability analysis.

The City’s hydraulic model was used to evaluate the capacity adequacy of the existing system

and to plan its expansion to service anticipated future growth.

6.1 HYDRAULIC MODEL SOFTWARE SELECTION

The City’s hydraulic model combines info

rmation on the physical characteristics of the sewer

system (pipelines, lift stations) and operational characteristics (how they operate). The hydraulic

model then performs calculations and solves series of equations to simulate flows in pipes,

including backwater calculations for surcharged conditions.

There are several network analysis software products released by different manufacturers that

can equally perform the hydraulic analysis satisfactorily. The selection of a particular software

depends on user preferences, the sanitary sewer

system’s unique requirements, and the costs for

purchasing and maintaining the software.

The hydraulic modeling software used for evaluating the capacity adequacy of the

City’s

sewer

system, InfoSWMM by Innovyze Inc.,

utilizes the fully dynamic St. Venant’s equation which has a

more accurate engine for simulating backwater and surcharge conditions, in addition to having the

capability for simulating manifolded force mains. The software also incorporates the use of the

Manning Equation in other calculations including upstream pipe flow conditions.

The St Venant’s

and Manning’s

equations are discussed in the System Performance and Design Criteria chapter.

6.2 HYDRAULIC MODEL DEVELOPMENT

Computer modeling requires the compilation of large numerical databases that enable data input

into the model. Detailed physical aspects, such as pipe size, ground elevation, invert elevations,

and pipe lengths contribute to the accuracy of the model.

Pipes and manholes represent the physical aspect of the system within the model. A manhole is a

computer representation of a place where sewer flows may be allocated into the hydraulic system,

while a pipe represents the conveyance aspect of the sewer flows. In addition, selected lift station

capacity and design head settings were also included into the hydraulic model.

Developing the hydraulic model included system skeletonization, digitizing and quality control,

developing pipe and manhole databases, and sewer loading allocation.