Data Model Question: Relined(rehabilitated) Sewer Mains

[GrahamW]

HI,

I'm about to implement a way to store information about sewermain relining.

currently we have a separate dataset(polyline) for:

• Pressure sewer


• Gravity Sewer


• Encasements

and various point datasets.

How are other utilities addressing sewermain relining.

As I see it there is 3 options:

1. Attributes on the current main about method and date(and additional info stored in the AM system)


2. Separate dataset for relining to be symbolised to represent this


3. Overlapping copy of the same dataset(which is against our corporate cartographic standards(Self intersect/overlap))

I'm leaning towards number 2 then number 1 which is why i can't decide.

Regards Graham,

[HowardCrothers]

Graham,

I'd be interested to hear what other utilities think about this, so hopefully you'll get some good responses.

From the Esri perspective we typically observe utilities going with approach # 1 -  tracking lining via an attribute or attributes of the main.  If a utility has an enterprise asset management system than extended lining information is typically stored there with a relationship to the pipe in GIS via a unique ID.

I think the benefit of this approach is that it's less time consuming and less prone to error to maintain lining information as an attribute of the main then maintain separate overlapping feature classes.  Also maintaining lining information as an attribute makes reporting easier.  You can then use the attributes to symbolize lined mains differently from unlined mains.

The drawback to this approach is that it presupposes that all of your lining is always done on an entire main (running manhole to manhole), but in our experience it almost always is.

[JoshuaDamron]

The Public Works Dept. I work in has taken the same approach as Howard discussed, tracking the new pipe via the attribute table.

We have taken the view that a cured-in-place /sliplined pipe is typically designed to be a new structural pipe, not at all reliant on the old pipe it replaced.  Therein we have simply updated the pipe materal field from pvc, asbestos concrete, etc. to "sliplined" and given it a new installation date.

While we have not built an enterprise asset management system, one obstical we have yet to hash out is how to map point repairs. 

I think this is a great discussion topic, I look forward to hearing others input.

[MikeLouwrens]

When we reline pipes we note it only with attribution - we update the pipe material in our AMS to show it has been relined.  We change it to include both materials, as on outside of pipe will be one material (handy if looking for a specific pipe) and inside will be the new material.  We will also have another attribute that just flags it as having been relined.  Most important change we make however is the life-expectancy, as this will be extended as a result of the relining.

So looking at your 3 options, I'd go with #1.  I think you've already ruled out #3, and to me #2 doesn't really fit your existing model - the relined pipe is still a gravity sewer (for example), so really all that has changed is info about the pipe, not the function of the pipe itself.  Symbolising to show that a pipe is relined only makes sense if you already symbolise other lines based on their material.  If you symbolise based on function (as we do), then material should be irrelevant, and identifying the pipe through the GIS to find material (or similar) attribute should be adequate.

HTH

Mike.

[JoshuaDamron]

Most important change we make however is the life-expectancy, as this will be extended as a result of the relining.

Not to change the direction of this post, but a question for Mike (or anyone else with thoughts):

How does your asset management system track life expectancy?  Do you give it a year of expiration or does it count down the life left based on the year installed (2010 + 50yrs)?

Thank you,
Joshua

[MikeLouwrens]

How does your asset management system track life expectancy?  Do you give it a year of expiration or does it count down the life left based on the year installed (2010 + 50yrs)?

We have an install date for the asset, and then an expected life (in years).  I believe if we rehabilitate the asset we add years to the expected life (so the original install date doesn't change).

So for example an asset install in 1970 with an expected life of 50 years would be due to be replaced by 2020 (1970+50).  If we then rehabilitate the asset which gives it an extra 20 years we'll adjust the 50 to be 70 (1970+(50+20)).  That is my understanding of how we handle life expectancy.  I will check with my colleagues to make sure I've got this right though 🙂

Cheers,
Mike.

[KarenCarr]

Back to the original question, if you set up a relationship between a gravityline and rehabilitation data, is it possible to symbolize the gravitylines that have rehab data, and is it possible to query the rehab data? We have engineers that like to see on their map which lines have been rehabbed, and on occasion they want a report showing the lengths of gravitylines that have been rehabbed. Currently we are using the overlapping method, but I haven't been happy with the results and would like to use something more efficient.

[MikeLouwrens]

Back to the original question, if you set up a relationship between a gravityline and rehabilitation data, is it possible to symbolize the gravitylines that have rehab data, and is it possible to query the rehab data? We have engineers that like to see on their map which lines have been rehabbed, and on occasion they want a report showing the lengths of gravitylines that have been rehabbed. Currently we are using the overlapping method, but I haven't been happy with the results and would like to use something more efficient.

Hi Karen,

In ArcMap you are able to symbolise based on multiple fields.  So if you have one field where you record type of pipe (gravity, pressure, etc.) and another field you record whether its rehab or not, then symbolise differently for the rehab=Yes and the rehab=No.

Is this what you mean?

Mike.

[KarenCarr]

Ok thanks Mike, I understand that we could add a field showing whether the gravityline has been rehabbed or not (yes/no), but is it possible to query the rehab data that is related to the gravityline? For example, we would like to know how many feet of line were rehabbed for a particular rehab project. Or in the case of rehabbed manholes, how many had a chimney resealed? This is information that would only be available in the rehab data, not in the regular geodatabase.

[MikeLouwrens]

Ok thanks Mike, I understand that we could add a field showing whether the gravityline has been rehabbed or not (yes/no), but is it possible to query the rehab data that is related to the gravityline? For example, we would like to know how many feet of line were rehabbed for a particular rehab project. Or in the case of rehabbed manholes, how many had a chimney resealed? This is information that would only be available in the rehab data, not in the regular geodatabase.

I understand you now (that's what happens when I reply on a day off).  I'm not sure if I can help much though - we store very little at all in our geodatabase, all asset information is stored in our asset management system.  Any rehab info would likely be stored as Work order information or inspections after the rehab has been carried out.  We can access this info if we need it (not often needed through GIS) through ArcMap etc. through database joins or spatial views.

Mike.