Month: January 2021

Part 1: Why & How 2D Hydraulic Modeling is Enhancing Bridge Engineering

Image of colorful 2D hydraulic modeling image with arrows indicating which way water flows

A bridge, culvert, the road nearby or above, the banks, and the surrounding ecosystem are affected by water’s flow. It is no surprise, then, that studying hydraulics and hydrology when designing bridges is paramount for safety, road users, and engineers.

The purpose of hydrology is to study water itself with respect to the land, whereas hydraulics studies what the water is doing within a channel or pipe. So, when engineers develop 2D hydraulic models, they are looking at how water behaves in a given area, and ultimately use that information to build safer bridges. This type of modeling tells engineers not only where the water is going, but where it wants to be.

Basically, 2D modeling determines and depicts water flowing back and forth (on a horizontal plane) instead of horizontally and vertically (3D modeling). The modeling is presented as a dynamic graphic that shows the flow of the river or water body. With a bridge in the model, engineers can determine how the water will move around piers and abutments (the bridge foundation), what could happen with scour and decide how to design for it, and predict the bridge’s impact on the environment (and the environment’s impact on the bridge) for years to come.

2D hydraulic image of black water on a map with white, moving lines showing water flow direction
2D hydraulic model

First things First

When a bridge engineer designs a bridge or culvert associated with water, hydraulic modeling isn’t an afterthought; it’s one of the first things that gets done when a project starts. Structural engineers already have data about the area and usually the existing bridge. Still, they often need more specific information to understand the entire project better – for example, data points on the lowest part of the bridge and how the structure is situated in relation to the water below.

2D hydraulic modeling at the beginning of the project gathers that information and helps the engineers better plan for the project, and is welcomed by this engineer as a preferred alternative to the conventional 1D modeling. It’s not just a benefit to engineers who want to know a system’s details, though. Clients, municipalities, and everyday citizens benefit from engineers using 2D hydraulic modeling – because it helps convey to them what’s happening with the water and helps the engineers better protect the infrastructure we use every day.

When it Rains, it Pours

When you think back to the Mother’s Day floods in 2006 or any other time flooding threatened New England, you probably don’t think much about the bridges you drive unless the water pools over the road. What few people think about is what’s happening under and over the bridge; with faster rushing waters and more force, there’s the potential for three big events: scour, rising water carrying debris, and pressure on the bridge caused by flooding water.

Scour is what happens when sediment around the bridge foundation (or along the roadway) erodes and starts washing downstream, leaving the potential for the material under the bridge to become unstable. In some cases, sediment from upstream of the bridge will wash downstream and fill in these holes during the storm before anyone realizes how big of a scour hole actually developed. We use 2D hydraulic modeling to help better predict the scour that might occur during these events even though we may not see it.

Image of a flooding truss bridge in Ludlow, VT during a large storm

This erosion can also occur beside and/or below the roadways leading up to the bridge if the water flows over the roadway. The 2D model enables us to see how much of the water is going over the roadway as well as provides us with the depth and velocity of this water. We can use this information to determine if the sides of the roadway might be in danger of washing away with the water. If the embankments might erode, we can properly armor them and keep them protected.

Part of our job is looking out for this erosion – if we determine that scour might be a potential issue during a storm, we can get ahead of it. One way of doing this to help prevent it under the bridge is by putting riprap (larger stones) in front of and around the bridge foundation to help keep the natural, finer sediment of the streambed and below the foundation in place. Another way is potentially changing the foundation type: if the anticipated scour is deep, we might change from a shallow foundation to a deep foundation. Scour is just one of the dangers associated with large storms, and 2D hydraulic modeling gives engineers the insight they need to help prevent dangerous situations.

Rising water is another danger to bridges, not just because it could potentially overtop (flow over) the bridge, but because the rushing waters can carry debris (say, a fallen tree) that could hit the bridge and cause damage. When we plug in potential flooding scenarios into the 2D hydraulic models, we use the models to predict how high the water could potentially get during a storm. That way, we can plan to build a new bridge or raise an existing bridge above the water level, reducing the chance for the bridge to be damaged.

2D hydraulic image showing velocity and water flooding on top of bridge

The third big concern with large storms is the power of flooding waters pushing on the bridge. This pressure could be going into and on top of the bridge, but also could come from under the bridge (buoyant forces trying to lift the bridge up). For this scenario, 2D hydraulic modeling allows us to see where the water would want to go during a flood and determine how much of it is going under the bridge, over the bridge, and around the bridge. This allows us to evaluate what an existing bridge might experience, and to design a new bridge to eliminate these forces (locate the deck above the water) and to resist the forces that can’t be eliminated for a certain storm event.

Garbage in, Garbage Out

The more data we can put into the model and the more accurate that data is, the more confident we can be with the results. That means that for the most part, 2D hydraulic modeling provides valuable information that we had to assume or make educated guesses about 30 years ago. While 2D hydraulic modeling doesn’t solve every problem, it gets us closer to understanding the hydraulics of the bridge. In the event that a solution doesn’t quite make sense, it could be because we need more or better data to put into the 2D hydraulic model.

For example, we’re working on a project right now that is analyzing an existing bridge in a river. Using 2D hydraulic modeling, we noticed that the water isn’t flowing as expected. We looked upstream and noticed old bridge abutments causing a constriction in the water flow. This slight constriction causing the river to backwater and holding part of the flow back is a great example of how limited data can affect the hydraulic modeling, or what I like to call “garbage in, garbage out.” If we didn’t have the data that depicted this constriction, we might have missed how it influences the river and the flow at our crossing.

Another project currently underway involves an upgrade and analysis of two culverts, with a third culvert right upstream, that have all been causing water constriction. The 2D hydraulic model shows us how these constrictions are causing backwater and increased flooding. The 2D hydraulic analysis also allows us to see what happens when we change the structures in the water. With some tweaks to the 2D model, we’re able to see that if we replace the two downstream culverts with a wide open structure that spans the bankfull width, the flooding is significantly reduced in the model. Meaning that if we replace these culverts with this other bridge system we designed, the next huge rainstorm won’t cause so much issue.

Want to know more about 2D hydraulic modeling?

We’re only as good as our data and our engineers’ analysis of that data. 2D hydraulic modeling has helped us foresee challenges to certain bridge structures while advocating for others to serve an area better. It replaces 1D hydraulic modeling at a time when computers now have the bandwidth to handle the massive programs required to use.

If you have any further questions, reach out to me and stay tuned for the follow-up blog on the different programs and math needed for this undertaking!

All About LPA: A Valuable Funding Source for Maine Transportation Projects

We’re excited to have another professional get LPA certified in Maine! Sean James, PE, Senior Vice President, joins our growing number of LPA certified project managers, engineers and technicians who can coordinate on these specific projects. Sean has worked on dozens of LPA projects in the state of New Hampshire and is looking forward to bringing his tenured experience to LPA projects in Maine.

What is an LPA Project?

The Local Project Administration (LPA) program leverages local dollars with state or federal dollars through the Maine Department of Transportation (DOT) on a wide variety of projects statewide. These projects can include resurfacing and rebuilding of roads, intersection improvements and non-vehicular transportation alternatives such as sidewalk and shared-use paths, pier and float installations and bridge and culvert replacement.

 
Who is Eligible & for How Much?

An LPA project can be administered by a variety of organizations including municipalities, regional transportation agencies, education institutions and tribal governments. The selection of projects is competitive and includes a variety of programs including Transportation Alternative, Low-Use Redundant Bridge Program, Small Harbor Improvement Program and the Hazard Elimination Program. Funding reimbursement varies from 50 to 80 percent of the project’s eligible costs.

Is there Certification Required?

LPA program certification is required for all projects that include federal funding; however, the training is beneficial for non-federally funded programs as well. The certification program covers the financial aspects of projects, hiring consultants, project design including environmental review, utility coordination, Right-of-Way and construction administration. Hoyle, Tanner’s team includes LPA certified professionals who understand the program and assist our clients in meeting their project goals.

The Role of Consultants

Engineering consultants act as an extension of the owner’s organization and bring specialized technical and funding program experience to the project. The consultant’s role is to understand the purpose and need of the owner, to study and provide alternatives for consideration, turn the project vision into a final design and permit the project and finally provide assistance with bidding and construction administration and oversight as well as final project closeout for reimbursement. 

The LPA program provides opportunity to improve our communities while minimizing the cost to local budgets. Our bridge, transportation and environmental teams have a wide variety of design and construction experience with LPA projects including bridges (vehicle and pedestrian), sidewalks, roadway improvement and safety and intersection improvements. For more information on how to get started and how we can assist in meeting your project goals, please contact Sean.

The New Great Bay Total Nitrogen General Permit

Pink and purple sunset image over water with tree skyline of Great Bay Estuary

What is the Great Bay Total Nitrogen General Permit & why does it matter?

The US Environmental Protection Agency (EPA) issued the final Great Bay Total Nitrogen General Permit (GBTNGP) on November 24, 2020. The GBTNGP is aimed at reducing the overall nitrogen loading into Great Bay, a unique coastal marine estuary. The GBTNGP covers discharges of nitrogen from the 13 communities that own/operate wastewater treatment facilities in the watershed: Dover, Durham, Epping, Exeter, Milton, Newfields, Newington, Newmarket, Pease Tradeport, Portsmouth, Rochester, Rollinsford and Somersworth. The permit allows for an adaptive management approach to monitoring and reducing nitrogen discharges. Each community has the option of being included for coverage under the GBTNGP or not (opt in or opt out). If a community decides to be included for coverage under the permit it must file a Notice of Intent with the EPA, Region 1, by April 2, 2021. The alternative to opting in to the GBTNGP will be that the community will receive a new/revised individual NPDES permit to govern its WWTF discharge. Key dates for actions to be taken pursuant to the GBTNGP are as follows:

  • February 1, 2021 – Effective date of the Great Bay Total Nitrogen General Permit.
  • March 31, 2021 – Deadline for finalizing an Intermunicipal Agreement to develop the Adaptive Management Plan.
  • April 2, 2021 – Deadline for sending EPA the Notice of Intent to Opt-In to the TN General Permit.
  • July 31, 2021 – Deadline for submittal to EPA of the Part 3 Adaptive Management Plan.

How can an Adaptive Management Approach help?

The GBTNGP allows for an adaptive management approach to be taken for monitoring and controlling nitrogen discharges and allows for the communities to develop the Adaptive Management Plan. Adaptive management is a key aspect of watershed management and restoration. Elements of adaptive management included in GBTNGP involve ambient monitoring, pollution tracking, reduction planning, and review. Adaptive Management is, by definition, a structured iterative process of robust decision making in the face of uncertainty, with an aim to reducing uncertainty over time via ongoing system monitoring. In this way, decision making simultaneously meets one or more resource management objectives and, either passively or actively, accrues information needed to improve future management and decision-making. Adaptive management is a tool which can be used not only to change a system, but also to learn about the system (Holling 1978). Because adaptive management is based on a learning process, it improves long-term management outcomes. The challenge in using the adaptive management approach lies in finding the correct balance between gaining knowledge to improve management in the future and achieving the best short-term outcomes based on current knowledge (Allan & Stankey 2009).

A holistic & cost-effective approach.

The objective of an adaptive management approach is to take a broad holistic and more cost-effective approach to implementing water quality restoration and management measures that will achieve better overall results in improving water quality goals in less time and at less cost than the traditional regulate-react approach by applying limited resources where they will have the greatest effect. In fact, the GBTNGP encourages sharing of resources and costs among the participating communities. The adaptive management approach allows for planning, implementation, monitoring and refinement in order to maximize the results with limited resources (resource optimization). The idea behind an adaptive management approach is for communities to become proactive rather than reactive in restoring water quality within the watershed. A successful adaptive management approach will require extensive collaboration and cooperation between municipalities, regulators, agencies, volunteer groups and other watershed stakeholders.

Our experience.

Hoyle, Tanner’s Northeast Municipal Engineering services Group (NEME) employs 20 engineers whose primary focus is water quality engineering – wastewater, stormwater and drinking water. Our depth and breadth of experience includes working with communities to assist them with compliance with permits such as NPDES (wastewater and stormwater), MS4 (stormwater and non-point) and a host of other regulatory and environmental permits. We have been working with communities under regulatory constraints to monitor and reduce the amount of total nitrogen discharged to local water bodies and helping them to achieve water quality goals. Jennie Auster, one of our wastewater process engineers, has been working with communities affected by the Long Island Sound Total Maximum Daily Load (TMDL) for Nitrogen for over six years including completing biological nutrient removal analysis for several facilities. Jennie completed nitrogen removal optimization plans for six communities and has presented at the Green Mountain Water Environment Association Technical Sessions on her experience with low-cost nitrogen optimization plans (presentation available upon request). We are assisting several communities on compliance with the 2017 MS4 permit which includes nutrient reduction in stormwater and non-point sources. We are also working with many communities on asset management for their wastewater, stormwater and drinking water systems, the goal of which is resource optimization to improve decision-making and maximize the life of the infrastructure.

Let us help!

Our team has a history of developing creative and innovative solutions to help clients achieve their goals in cost-effective ways while optimizing the use of limited resources. For more information please visit our website at: www.hoyletanner.com or contact Michael Trainque or Joseph Ducharme.

I am a Senior Environmental Engineer and Vice President at Hoyle, Tanner, and chairman of the Board of Directors of the Southeast Watershed Alliance (SWA). The SWA is a non-profit watershed organization for which enabling legislation was enacted by the NH State Legislature in 2009 encompassing the 42 communities in the NH coastal watershed. I have been following the development of this permit on behalf of clients.

Preparation Tools for Snow and Ice Control at Your Airport

Many of us have already been impacted by the arrival of snow and ice this winter season. Fortunately, our nation’s airport operators have been preparing for this wintery mix long before the first snowflake arrived. These airport operation professionals understand the vital role our Commercial and General Aviation airports play in the country’s transportation system and the importance of keeping them open and in safe operating conditions during every season.

HAZARDOUS CONDITIONS

Airport operators have many tools to assist with mitigating hazards created by winter weather. Perhaps the most important being an up-to-date Snow and Ice Control Plan (SICP). A comprehensive SICP includes a detailed game plan to address hazardous pavement conditions that may develop from any winter weather. This would include something as important as ensuring reliable communications between all entities involved in the airport operation. Snow crews, who are responsible for the airfield safety, must be able to coordinate airfield maintenance operations with Air Traffic Control, individual aircraft, and airport tenants. They share crucial information regarding the pavement conditions including the presence of contaminants such as snow, ice, or slush, all of which have the potential to negatively impact aircraft. Equally as important, they coordinate personnel shifts to ensure their staff is rested and able to fulfill their duties.

ICE COMMITTEE

The basis of any SICP starts with identifying a Champion of Winter Ops Safety, usually the Airport Manager or Director of Operations. It is the Champion’s job to gather support and build a guiding coalition also known as a Snow and Ice Control Committee. Preferably, this committee is made up of individuals working in varying roles throughout the airport. This ensures proper preseason planning has addressed every area of the airport and every individual operation focused on improving airfield safety and communications. Establishing this stakeholder group early helps build a solid communication base and creates a culture where communication and ongoing operational evaluations meet the needs of airport users.

Some considerations for airport managers before the snow season should include:

  • Establishing a Snow Control Center (SCC) for snow and ice control activities. This can be as simple as the cab of the operator’s snowplow, a desk in the manager’s office or Fixed-Base Operator, or a special office dedicated to snow operations. The priority is that there is a known official command center that is responsible for clearing the Airport Operations Area, disseminating information related to current field conditions, issuing Notice to Airmen (NOTAM), and if necessary, closing runways or areas on the airport unsafe for aircraft operations.
  • Establish airport snow clearing priority areas. This identifies areas that are essential to the safe operation of the airfield. Priority 1 areas include the primary runway, associated parallel taxiways and route to the apron, essential apron area, and emergency staging and access points. Less essential areas, known as Priority 2, can be prioritized and cleared as operators regain control of the situation. These include crosswind runways, supporting taxiways, other airport facilities areas, and additional aircraft parking areas. Priority 3 areas are all other surfaces in the Airport Operations Area, including all access and perimeter security roads. Airport Managers should identify areas that tenants are responsible for and request SICP’s from individual tenants at the airport.
  • Staffing for snow operations. Airport managers should (and if operating a certificated airport are required under Section 139.303 to), “Equip personnel with sufficient resources needed to comply with the requirements of the SICP,” and “Provide sufficient and qualified personnel to comply with the airport’s SICP.” Human factors can play a huge role in operational safety during snow operations. Realistically the snow season can last more than half of the calendar year with storms that can last for several days with little if any downtime. Managers should consider things like personnel training, snow ops crews (A crew vs. B crew), shift lengths including adequate rest periods, food and hydration, and resting areas on site.
  • Equipment Selection & Storage. The amount and size of Snow Removal Equipment (SRE) required to clear the airport is based on calculations laid out in FAA Advisory Circular 150/5220-20, Airport Snow and Ice Control Equipment. The calculations provide guidance on the types and size of equipment needed to clear the Priority 1 areas in a specified time period based on the average annual snowfall, type of airport and annual operations. In addition to the type and size of equipment needed to keep the airport operational, the FAA recommends housing the equipment in a building capable of maintaining 50 degrees Fahrenheit. This will help prolong the useful life of the equipment and to enable more rapid response to operational needs. The availability of a storage equipment building also ensures operators can inspect the equipment before and after use as well as make repairs and conduct routine maintenance throughout the snow season.

With the snow season upon us, airports across the county will be implementing their thoughtfully crafted SICP with the understanding that it may need to be evaluated and adjusted throughout the season.

If you plan to travel at any point during this winter season, pause for a moment to observe and appreciate the many hours of planning that occurs before a single flake flies that keeps your airport open and safe during winter operations.

Further detailed information and links to supporting documents where you can find guidance when developing a Snow and Ice Control Plan (SICP) can be found in FAA Advisory circulars, 150/5200-30, 150 and 150/5220-20.

Employee Spotlight: Kevin Preston

Kevin Preston, CADD Technician and White Mountain Hiker

1.  What drew you to Hoyle, Tanner?
I wanted to work in a smaller company environment than the one I was previously in, allowing more room for professional growth.
2. What’s something invaluable you’ve learned here?
The importance of communication.  I’ve never been the greatest communicator, personally and professionally, but I do try to get better at it all the time.
3. What’s your favorite time of year to work at Hoyle, Tanner?
I can’t say any time of year really stands out specifically over another, but I do enjoy seeing what everyone comes up with for decorations during Christmas.
4. What’s the coolest thing you are working on?
I’m working on a large project for a state agency. I have a soft spot for the larger projects and being able to say I worked on it every time I drive by would be pretty neat.
5. What’s the best thing that’s happened to you so far this week?
I received approval from a mortgagee to begin a search for a new home!
6. How many different states have you lived in?
Only New Hampshire! Although I was born in Massachusetts, oddly enough.
7. If you could only eat one meal for the rest of your life what would it be?
Shepherd’s pie
8. What kind of pet do you have and how did you choose to name it?
I have a 2-year-old Bernedoodle dog named Jackson. I named him after Mount Jackson in the White Mountains, one of the first 4,000-foot mountains I ever climbed.
9. What is a fun or interesting fact about your hometown?
I grew up in Bow, NH… Nothing fun or interesting comes to mind!
10. What are three things still left on your bucket list
1. Visit England, specifically take a trip to Anfield where Liverpool FC play.
2. See the Northern Lights.
3. Climb Mount Whitney in California, the tallest peak in the lower 48.

11. Name three items you’d take with you to a desert island.
1. A lighter
2. A tarp
3. Fishing equipment (practical enough)

12. What characteristic do you admire most in others?
Empathy
13. How old is the oldest item in your closet?
14 years old?  I moved into my current condo about a year and a half ago, many things disappeared in the move but there is a pair of soccer cleats from high school still kicking (no pun intended…) around in there!
14. Words to live by? Favorite Quote?
“Treat others the way you want to be treated.” It’s simple, but many problems could be alleviated by simply remembering it.
15. What did you want to be when you were growing up?
A professional soccer player.
16. If you were to skydive from an airplane what would you think about on the way down?
Which cord is the parachute?