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Draft Flow Risk Evaluation Package

Posted by Robert Czachorski on 13 Mar, 2014
Category: No category

Folks,

I am posting a detailed package of information that contains the preliminary flow frequency analysis and flow risk assessment. This information is preliminary and is still work in progress until we prepare the report, but we wanted to get it to you in advanced of the CAC meeting.  This is a major deliverable and represents the draft / preliminary summary of the past 3-4 months of work on the risk assessment. 

The document contains six (6) sections as follows:

  1. Model accuracy of fit tables
  2. Frequency analysis results
  3. Flow risk evaluation (at the metering sites)
  4. Priority District Pre- and Post-FDD Risk Comparison
  5. Climate Change Risk Evaluation
  6. Benchmarking evaluation

Each of these sections contains a cover sheet that provides a brief explanation and overview of the section. This package is entitled "Flow risk evaluation package", because it represents an analysis of the flows at the metering points. The hydraulic model that Murat is preparing will address the other major component of the risk assessment: the hydraulic capacity assessment of the pipes.  Murat will have preliminary findings on this component ready for the meeting next Thursday. 

When reviewing these materials, please note that the first section (accuracy of fits) is approximately half the document and contains a lot of detailed plots about the model calibration and performance. This is an important step to gain confidence in the model, but the more important and interesting findings are contained in the results in sections 2-6.

It is not mandatory that you review this package in detail before the CAC meeting, because we will be reviewing the results of the analysis together at the meeting next week. However, I thought I would share them with the whole group in advance of the meeting if case anyone is interested in drilling down into the details in advance.  This can be very helpful for generating a good discussion at the meeting.  I am happy to answer questions here on this packet in advanced of the CAC meeting, and we will also have 80 minutes dedicated at the next meeting to go over this as well as the preliminary hydraulic results.  Some of these concepts are much easier to discuss in person when we can dialog and draw sketches.  So plan on a detailed discussion next week.

Take care,
Robert

Comments

Joe Conen on 14 Mar, 2014:

Robert, would you forward this to Frank?
Thanks
Joe
By the way, I am having some tech issues and am not able to keep up on this info as much as I would like to, for now. Hopefully soon resolved.

Robert Czachorski on 14 Mar, 2014:

I should have mentioned in the post - it was sent to Frank and Bill Higgins by email concurrently to the post on Basecamp.  (Bill Higgins because he has asked a lot of questions over the last several months showing a great interest in this stage of the project).

Take care,
Robert

Joe Conen on 20 Mar, 2014:

Robert,
After a look through this, I have some questions and concerns. Maybe you would have time to look at these and discuss some of them tonight.
Thanks
Joe

Flow risk discussion items

 

Section 3 second sheet:

Priority areas capacity recurrence intervals:

Glen Leven pre FDD shows >100 year RF (less than 60 per cent of pipe capacity at 100y RF), yet that is a target area, so has a significant history of backups. Less extreme, but similar thought is Dartmoor, most of Morehead.  Are flows measured in appropriate locations? How can this be explained? Why would backups have been a problem in these areas?

Why does recurrence frequency not change at all for most of the Morehead locations? Morehead is more than 60 per cent disconnected.

While Glen Leven now shows greater than 100 year RF, the flowrate at 100 yr RF is comparable to the pre FDD 10 year, and the post FDD 10 year is still almost 70% of the pre-FDD, even though they are 56 percent disconnected.  Seems like footing drains may not be the major contributor to peak flow in this area.  Also, seems it will be difficult to get a reliable view of the risk in this area or the measures necessary to address this risk.

On the next table, “Recurrence Interval of the peak flow metering in 2013”, about a third of the metered locations approached or exceeded the 100y RF values (Morehead 1A exceeded the 100y RF twice? August 12 Storm table data is peculiar). This, to me, calls into question the validity of the 100y values. So, did A2 weather in 2013 offer storm intensities comparable to 100y storms?  What are we to make of this? Related; peak flows for Morehead 9B, B1 and G1 were not recorded for June 27 (or August 12) event that resulted in the 6 areas at the 100y RF. What happened (meters get flooded out)? Can we infer/predict what the peaks were based on model and other flow data?

General question: Were any sanitary backups reported in target areas in 2013 or 2012?

 

Section 4

Why is only one location in each district described (e.g. Morehead 49M)?  What kind of assurance does this provide for other locations (e.g. Morehead B1). What can we infer from this?

 

Section 5

Glen Leven post FDD still among the highest peak flow locations. Something else wrong here?

Also, even areas with near 100 per cent FDD (Bromley, Orchard) not that good. Mid pack.

Not sure what” capture percentage” is.


Kathy Boris on 20 Mar, 2014:

I am glad I looked at these tables before tonight's meeting.   Some things I understand, but a lot of it I don't understand.   I look forward to tonight's presentation by Murat and others which, I hope, will make everything clear.
kb