Computer Analysis Tool of Hydrosims

The first sewer model using general flow governing equations was called
Storm Water Management Model (SWMM), which was sponsored by the US
EPA in the early 1970’s.  The majority of the sewer modeling community has
considered the hydraulic simulation engine in SWMM and its principles as a
Standard approach.

The SWMM Extran is a major model component for hydraulic simulations of
sewer network. The numerical method used in the Extran needs user to have
significant experiences in “model polishing” in order to overcome the
numerical instability often occurred in the model simulations, especially for
those large and complex sewer systems. The earlier SWMM could only be
operated within the DOS operating system and had no user interface.  

Using principles similar to SWWM, SewerSIMs consists of St. Venant
equations, i.e. 1-D momentum and continuity equations. The strength of
SewerSIMs is its very robust simulation process due to the application of the
latest numerical approach and a user-friendly interface.
The model package
development was mainly sponsored by Shanghai Municipal Sewerage
Company during 1997 ~ 2004.
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The SewerSIMs can accurately simulate:
  • Free surface, surcharge flows and back- water effects
  • Gradually varied flow in pipes and rapidly changing flow
    in control structures
  • Hydraulics of looped networks

A sewer Hydrology/Hydraulic model and a well-trained user
team could be a very powerful tool to accomplish following
objectives as:

Simulations for Design Evaluation

SewerSIMs can be used by modeling engineers to simulate:

  • Combined sewer overflows (CSO)
  • Sanitary sewer overflows (SSO) together with storage
  • Open and closed conduit flow and impact of new site

Therefore, the advanced computer modeling technology is able
to scientifically answer questions posed by decision-makers
and engineers, such as:
  • What are the return periods for overloading of various
    parts of the existing sewer system?
  • What is the major reason of overloading (backwater,
    insufficient pipe capacity, insufficient hydraulic control
    structures or operational problems, etc.)?
  • What is the impact or cost effectiveness of replacing
    critical sewers, installing new detention ponds, outfall
    structures, etc?

A well-established modeling system can be further applied to
predict both short and long-term environmental impacts
affected by changing operational policies.  The SewerSIMs
model can be employed at any stage within a sewer project’s
development cycle, from the planning area, to the design stage,
and onward into system operations and maintenance.  In
addition, through adding other program components, a
SewerSIMs model system can be expanded to become a
complete sewer information management and control system.
Simulations for Operation Strategies

The model simulations could be carried out to develop
operational strategies for pumping stations for power saving,
flooding and CSO control.  For example, in some area of
Shanghai, sewer overflow occasionally occurs under the dry
weather flow condition while the usage of capacity of main sewer
conveyors is less than 50%. The SeweSIMs was used to
examine the impact of static and reactive control strategies on the
behavior and performance of the existing sewer network. The
optimized control strategies were developed for the SMSC staff
and Engineers and the dry weather sewer overflows were
eliminated through using those optimized operational rules.

Optimization for Hydraulic Structures Upgrade

To effectively use the storage in the system needs two conditions:

  • Enough control structures in the system to “hold” or
    “release” the flow under certain conditions
  • Optimized operational strategies to store more water
    without increasing the risk of flooding

For a large and complex sewerage and drainage system, it is
possible that during a storm, flooding or CSO’s occur in the
service area of the main sewer conveyors while in some portions
of the system conveyors or collection pipes are empty. Using
SewerSIMs, the modeling results for the existing sewer and
drainage system could be analyzed to identify the drainage area
lack of enough control ability.
Project Delivery
The major advantage of a sewer modeling project is not only to
present a project report but also provide the project owner the
sewer hydraulic and hydrology model package together with an
established hydraulic/hydrology model system jointly with
solutions for flooding and CSO control.  The model system could
be further used by owner’s team to timely evaluate a system
retrofit alternative with limited effort.
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