Hydraulic Model and Subsequent CIP for Water Distribution System
The City of Woburn hired Weston & Sampson in 2013 to assist in developing a hydraulic model and subsequent capital improvement plan (CIP) for their water distribution system. As part of this effort, Weston & Sampson pursued a strategy that allowed the city to retain hydraulic model attributes within their Geographic Information System (GIS). Doing so provided the city with a means to maintain up-to-date model input data.
Weston & Sampson acquired the water system GIS and performed a preliminary evaluation on the data. First, a gap analysis of the attributes was conducted to ensure that all necessary information for the model was contained. Then, an assessment of feature connectivity was performed using network tracing to confirm that the network was fully integrated. Topology definitions were employed to enforce strict adherence to the design criteria and to make sure that interconnections at pipe intersections were properly represented. Where data was incomplete, Weston & Sampson presented the data gaps and coordinated with the city to populate the necessary information. Within the GIS, a roughness coefficient was assigned to each segment of pipe based on known conditions. In addition, nodes were created at each of the pipe ends.
Attributes specific to the operation of the model were then available for incorporation into the GIS. These attributes included populating the newly added nodes with elevation and demand data. To assign elevations, Weston & Sampson used a Digital Terrain Model (DTM) derived from the USGS LiDAR for the Northeast project. The benefits of this data and information are that it is recent, extremely accurate (30cm Fundamental Vertical Accuracy), and publicly available. Elevations were extracted from the DTM at node locations and assigned to the nodes in an automated process. Demand data available from the city was similarly assigned using a scripted process.
With the model information established within the GIS, Weston & Sampson then exported and modeled the data, observed the results, and made recommendations for the CIP.