Moving into the Next Century with GPS

Feb. 1, 2000
A highly accurate wastewater database is an optimum strategy for a utility. Over the past 15 years there has been a traditional approach championed from the engineering side of the organization to converting wastewater infrastructure data by digitizing existing wastewater atlas maps or as-builts. This approach is economical, yet relies solely on the accuracy of the paper map. A separate and non-related task is inventory and inspection of the wastewater system by field operations. Both groups are

A highly accurate wastewater database is an optimum strategy for a utility. Over the past 15 years there has been a traditional approach championed from the engineering side of the organization to converting wastewater infrastructure data by digitizing existing wastewater atlas maps or as-builts. This approach is economical, yet relies solely on the accuracy of the paper map. A separate and non-related task is inventory and inspection of the wastewater system by field operations. Both groups are attempting to accomplish the same outcome of accurate and current information, which facilitates optimal management of tasks.

However, as is typical of many organizations, the information highway is not perfect, In many cases it is nonexistent. Each entity must make decisions on information they trust, but the information is different to each group. Getting this information together in one authoritative source would be helpful. In a perfect world, information will always be precise, current and easily accessible.

In order to develop a business case we must address a few major areas: accuracy, currency, accessibility, and cost. An engineer would most value accuracy in a spatial data system. The need for spatial accuracy is driven by the fact that the engineer must design and build wastewater infrastructure with sub-meter precision.

However, field operations will place higher value on current data. The latest data allows field crews to make quick informed decisions with confidence. Many existing map records of the wastewater collection system are incorrect or incomplete. A digital map database and inventory of wastewater systems are essential in assisting with establishing asset management and priorities for rehabilitation of mains and manholes.

A wastewater system experiencing major problems during rain periods with infiltration and inflow (I & I), for example, would be particularly sensitive to this problem. An I & I problem like this creates overflows within the system and at the wastewater treatment plants.

Depending on the age of the system, a high percentage of the collection system may have deteriorated to the point that severe blockages are occurring in the mains and manholes, thereby creating additional flow problems in the system.

Most importantly, with the pressures of competition for budgets, employees must have quicker access to data when completing tasks. The need for data access transcends the organization and technology has provided increasingly more mobile ways to accomplish this requirement.

Finally, in a perfect world, organizations must spend money to make money. A case for cost benefits can easily be developed; particularly if a link can be established between current results and the lack of accuracy, currency, and accessibility of information.

The most promising outcome of today?s technology trends is the ability to generate high quality and accurate data using relatively inexpensive tools. An additional plus is that much of this technology can be used by less skilled people than in previous years.

It is very feasible for the municipal utility departments to use these tools without hiring subject experts or investing in expensive training programs.

Field Survey Location

To build a spatially accurate database the most important task is capturing the building blocks of your system (wastewater node features) with the most accurate cost effective method. The good news is that GPS (global positioning satellites) survey methods have been developed to the point that submeter accuracy can be obtained quickly and efficiently using lower-cost hardware.

Differential GPS (DGPS) satellite services are the most effective way to collect GPS information quickly and maintain submeter accuracy. The principal idea behind differential GPS positioning is to generate corrections for biases resulting from selective availability and other sources at one location using measured biases at one or more base stations. A GPS reference receiver at a base station tracks all GPS satellites in view, and by differencing the predicted location of each satellite and its measured location computes the pseudo-range corrections that are transmitted in real time to the DGPS users. The DGPS units are cheaper and will have an additional antenna receiver built into their standard GPS equipment to receive the correction data via geo-stationary communications satellite. However, they can?t be used for many higher-end GPS functions such as RTK (real time kinematic).

In summary, DGPS techniques eliminate the need for base stations to be set throughout the project area and create a ?virtual base station solution? that maintains the same accuracy over the entire coverage area. Crews can be mobilized instantaneously to collect data and not have to worry about coordination with a GPS base station.

Digital Video Survey

Since you are visiting each manhole during the survey of all the surface features, it is a good time to inspect and record the condition of rim, casing, mains, inlets and outlets of the system. The video technology recently has moved to the digital world as well, which allows us to truly create a digital data system. Trained field crews can use systems that fit in belt packs.

The advantage that digital technology affords is that the imagery and audio can easily be edited in the field or back at the office. The most exciting factor is the ability to store and retrieve all digital video and still photos through a GIS/CAD software system. Additional applications are the ability to add redline information directly on the image or enhance areas of poor visibility through image processing software.

Digital images can be transmitted through computer networks by e-mail or other methods promoting data sharing and quick collaboration with other departments.

While the field survey group is gathering coordinates and video, they can use a pen-based computer to input a number of field attributes such as manhole number, rim type, size, invert(s) depth, pipe diameters, and closest street address. These attributes will be imported into the GIS system and linked using the unique manhole identifier. A data collection guideline for all work orders either in-house or contracted is important to ensure easy integration to a GIS.

Database Generation

With the inventory complete, the system now has all the needed information to generate a wastewater network. By simply importing your field location data into your GIS software system you now have all node features captured.

The two major steps to complete your database are creating the wastewater mains and adding any additional attributes or annotations not captured during the field inventory. The mains should be as easy as connecting the manholes and extracting the attributes from the node features.

The database design should make use of annotations such as ?Smart Text? or text that is displayed from attributes stored in the database. This optimal strategy of storing all annotations as attributes allows more efficient means of database updates by only making a single point of data maintenance.

Benefits of Success

After the creation of the wastewater database, the data can be used confidently for many applications. These might include:

  • Sewer flow modeling: Most wastewater modeling software packages allow easy data importing into their systems and with a 100 percent complete online digital collection system your solutions will be very accurate.
  • Basemap for designing new systems: Instead of the engineering group sending out a survey team to create a base map for designing new or replacement systems, they will have a complete system at submeter accuracies.
  • Focused workflow for system rehabilitation: The ability for a technician to search the database and identify all areas that were flagged as needing rehabilitation during the video surveys will greatly improve mission planning. Also, engineers can access the digital data on-line in and select features, and view the digital still photos or digital video information.
  • I & I flow modeling: Having a complete system with the capability of instant access to updated the imagery of the system allows engineers to extract model data and run models with minimal need for additional field information.

In the area of field operations, a number of applications exist for the newly available data:

  • Asset management: A major function of most field operations is the daily management of all the assets that make up the system. Having an easily accessible database that is current and accurate within a meter will integrate with mainstream asset management tools.
  • Asset location: How many hours are lost to a crew?s inability to locate a certain asset? A complete network located on a mobile computer will clearly eliminate these problems. The submeter accuracy will allow crews to use GPS equipment to literally drive them to the exact location.
  • Field crews will need to spend less time driving around and visually inspecting manholes and mains. The onscreen video imagery can answer many of the questions that are generated when planning rehabilitation strategies.

Conclusion

There still are many factors that impact the success of a project. The major barriers will be the failure to mandate rigid and frequent data maintenance procedures to ensure that the data users are always confident that they are working with good data for their applications. Lack of proper access to the data for all parties can also encourage departments to invent their own methods of data collection.

Also, even though technology has become easier to use, it does not preclude us from understanding the principals upon which it was designed. When first implementing any new technology or process, a utility should involve subject experts to design and implement the approach. Nothing impedes a project more than delays due to the inability to implement technology effectively.

However, by using technologies such as DGPS and digital video systems, a utility maximizes its ability to meet users? needs and help the organization be more cost effective and successful in the industry.

About the Author: Kevin Trujillo is Director of Technical Services for Analytical Surveys, Inc.

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