The Mid-Atlantic Public Works Institute (MPWI) is developed so that practitioners provide their vast experience and share the knowledge base with public works personnel across many levels. Public works offers a broad scope of personnel, from line workers, to supervisors,  all the way to the Director position. Participants in the MPWI learn about the jobs and needs, where the training translates to and is identifiable with every position. For example, pointers on dealing with difficult employees also apply to service providers, contractors and residents.

The MPWI is a unique training ground collaboratively created between the Mid-Atlantic APWA Chapter and Virginia Tech University. The MPWI is an excellent opportunity for those in, or aspiring to be, in key leadership positions in the public works field, where after 96 hours of instruction, receive the certification of completion. Whether you are a team member on a small project or managing a multi-million dollar budget, it means coordinating, communicating, scheduling, and maintaining focus. Blending academic theory with the real-life processes, technologies, hard and soft management skills, and the best learning methodologies, MPWI can empower you to become a more effective leader and team member and to be confident in your ability to strategically execute projects and programs.

All classes are taught by practitioners and industry leaders with extensive experience in the field of public works. Participants gain strategic planning skills and managerial insight to be more effective project leaders. See more HERE

 The MPWI Steering committee has been meeting monthly, looking forward to its inaugural launch on September 22-24, 2015, and we hope to see you there! Applicants have the choice of attending the training at Virginia Tech University's Blacksburg, VA  or Newport News, VA campus locations.

If you would like more information, or wish to volunteer or help out at the September 22-24, session please contact Scott Smith at: [email protected]

The volunteer PWI instructors are: 

It's a Flume So it Must Be Accurate

The City of Lowell, Massachusetts had a shock when they installed an area-velocity meter in series with an existing flume.  Not only did the two not agree, but they disagreed by 40%. Which one was correct - the flume that had been installed 25 years earlier, or the new area-velocity meter?  With billings of $25,000 per month between the City of Lowell and neighboring Tewksbury, the stakes were high.

Lowell installed the area-velocity meter to read flows during surcharge conditions.  To reduce CSOs, they planned to store flow in wet weather conditions; this would surcharge the flume.  Area-velocity meters can read in surcharge so the plan was to do tag-team metering.

The area-velocity meter was installed during normal dry-weather flow conditions.  Once good readings were established, the project team looked for correlation between the existing flume and the new area-velocity meter.  Naturally, the project team assumed that the 25-year-old Parshall flume was accurate. However, the representative for new meter provided some compelling proof that the area-velocity meter was accurate.

FIGURE 1

Which meter was right?  The team looked for clues.  The first visual was the approach pattern to the throat of the flume (Figure 1).  Flumes require that "The approaching flow should be well distributed across the channel, and relatively free of turbulent waves. Generally a site with high velocity of approach should not be selected" (Isco Open Channel Flow Measurement Handbook, fifth edition, p. 65).

Standing waves, as seen in the approach of this flume, indicate either an improper approach velocity or flow in excess of the flume rating.  A team of two consulting engineers prepared an engineering memorandum summarizing

observations of the current flow conditions.  According to the report: "The primary flow element is a conventional manufactured Parshall flume. It has a 2-foot throat, with dimensions matching a conventional flume and is installed level and straight. The flow enters the station through a 48-inch diameter pipe. The plans for the original installation show the pipe entering the vault at an angle of 8 degrees 30 minutes with a slope of 0.00031. Measurements were that indicate the angle is about 4 degrees, 43 minutes and the slope greater than 0.007. The report noted that the measured slope was 20 times greater than the design slope, and that the transition from the Tewksbury interceptor to the flume was skewed, causing an imbalance in the approach velocity pattern (Figure 2).

FIGURE 2

The report further verified that the specifications of the area-velocity meter matched the requirements of the project, and that its settings were proper for the installation. The engineers made a series of measurements to confirm the observed flume problems. Their physical measurements started with velocities across the channel at two locations: 5 feet upstream of the flume and at the flow measuring point of the flume (Ha). They were able to confirm that the flow was in the "super critical" regime. According to the report: "The definition of sub and super is most easily remembered as related to the critical depth line of any channel for a 'given' flow rate. In hydraulics of open channel flow, this means that there are 'two' possible depths in any channel for any 'given or same' flow, one above the critical depth line and one below."

In other words, the unintended supercritical flow condition had caused the depth measurement at Ha of the flume to correlate to the wrong flow rate.

To visually prove that the approach velocity was causing the inaccuracy, the

FIGURE 3

engineers employed a little Yankee Ingenuity; they held a large wooden board in the upstream flow approach to dissipate the energy (See Figure 3). The results were a dramatic and almost instant increase of the flume flow reading to agree with the area-velocity meter.

The next step was to bring in an independent third-party expert in flow measurement. When Flow Assessment Services (Goffstown, NH) was called they said this is far more common than most people realize, and that it was hard to believe how many flumes or weirs are proven inaccurate.

Flow Assessment Services (FAS) suggested installing a third meter to see if it would correlate with either of the first two meters. FAS selected, with the client's approval, an area-velocity meter. After careful installation and calibration of the meter, the readings of the 3rd temporary meter matched those of the existing area-velocity meter. The temporary check meter was left in place for a period of 60 days. The results were conclusive: the two area-velocity meters agreed, and the existing flume agreed with these readings when the upstream velocity problems were addressed.

The City of Lowell tried hard to make the flume work once they learned of its shortcomings.  But short of ripping up an extensive metering chamber, their only recourse was to rely on the area-velocity meter for low flows to surcharge flows.

Provided by Jeff Cantwell, Flow Assessment Services, LLC. He can be reached at: Office: 610-918-3857 and email: [email protected] 

Congratulations to Our 

2015-2016 College Scholarship Recipients!

Kiren Ajrawat

Daughter of Seema Ajrawat

Chief of Administrative Services

County of Fairfax, Virginia

Major-Systems Engineering

George Washington University

Russell Martin

Son of Eric Martin

Director of Public Works

City of Chesapeake, Virginia

Major-Computer Engineering/Physics

College of William & Mary

Meghan Tait

Daughter of Cindy Tait

Public Works Analyst

City of Annapolis, Maryland

Major-Ecology

University of Georgia

[email protected]