District of Columbia Water and Sewer Authority,
USAHatch Mott MacDonald (HMM) of Millburn NJ and Michael
Baker Jr., Inc. of Alexandria, VA, were awarded a US$9million,
five-year contract by the District of Columbia Water and Sewer
Authority (DCWASA) to provide Engineering Program Management
Services for the water distribution system.
DCWASA provides domestic and fire protection services to the
District of Columbia, serving a population in excess of 500,000
people. DCWASA is responsible for the retail distribution of water
with average demands of approximately 135MGD.
The water system comprises approximately 1,300 miles of mains in
seven pressure zones. Storage for system equalisation and fire
fighting is provided in nine storage reservoirs and tanks. DCWASA
also maintains and operates four pump stations and approximately
36,000 valves and 8,700 hydrants.
The Joint Venture Team provides overall Program Management of the
water distribution system including planning, engineering design,
and engineering design management services.
An initial effort of HMM was to develop water distribution
hydraulic models that included all pipes within the water system
for the various gradient zones. These models were developed from
existing AutoCAD drawings of the water system, and were
georeferenced to the Maryland State Plane Coordinate System to
provide planning level accuracy for use and overlay with other GIS
data sets. The development of the models included extensive quality
control for the data conversion through the cross-reference of
detailed system maps to verify the accuracy of the AutoCAD base
map. Calibration of the models was developed through an extensive
review of available SCADA information, previous hydrants flow
tests, historical pipe coefficient test data, pipe materials data
coupled with date of installation, and additional field flow tests.
Several notable hydraulic analyses that have been performed
include:
Bryant Street Pump Station Analysis - prior to replacing 10
pumps serving four gradient systems, a detailed analysis of suction
and discharge hydraulics was performed for this 100MGD pump station
to determine cost effective pump selections for the anticipated
range of head conditions. An extensive operations analysis was
performed to determine the operating costs for various efficiency
pumps.
Modelling in Support of Valve Replacement Projects - the
current Capital Improvements Program (CIP) includes the replacement
of major valves within the water system which require extensive
shutdowns of existing water mains for valve isolation. Prior to
performing the field work, modelling is performed to identify the
interim pressures and hydrant flow capacities to identify any
potential adverse conditions.
Bryant Street Pump Station Surge Analysis - a skeletised
version of the water model pipe and node geometry was imported into
KYPIPE 2000 software to perform transient analysis in support of
ongoing rehabilitation at the pump station which includes the
replacement of existing surge protection devices. The analysis
includes recommendations for the opening/closing speed of the pump
control valves, and the pressure settings for surge control
devices.
Modelling in Support of Future CIP - the models were used to
perform global fire protection and pressure analyses to determine
locations requiring hydraulic improvements. The model is used to
evaluate multiple alternatives for water system improvements, to
determine which alternatives are cost-effective.
Saint Elizabeth's Hospital Tank - ongoing development within
the existing Anacostia First High Gradient System has reduced
available pressures and supply to customers. In order to improve
hydraulics, an investigation was performed to create a new sub-zone
with a proposed tank at a high elevation. The model was used to
validate the conceptual plan which included a new pump station;
tank; and pipeline improvements to maintain hydraulic capacity for
fire protection and pressures within the new subzone.
An additional effort by HMM included the development of an internal
web page that serves out GIS data using ESRI's ArcIMS. The GIS web
page includes many GIS data sets that are used to improve data
sharing and the analysis of distribution system conditions,
including:
- Input and output from hydraulic modelling assignments
- Locations of closed/broken valves
- Pipe material and condition inventory
- Topographic data
- Street centrelines with geocoding capabilities
- Hot links to scans of distribution maps; and
- Other environmental datasets
