Category: Design

Sustainable Drainage: What are the Techniques for Flooding & Protecting the Watershed?

Sustainable Drainage Systems are a collection of practices used to mimic natural processes of the hydrologic water cycle, which is the path of water as it moves around the earth and includes condensation, precipitation, infiltration, runoff, and evapotranspiration.  These sustainable drainage systems can consist of natural features or man-made features made to look and act like natural features (bioretention facilities, rain gardens, vegetated rooftops).  In the United States, Sustainable Drainage Systems are more commonly referred to as Best Management Practices (BMPs) or Low-Impact Development (LID).

What are Best Management Practices (BMPs) and Low-Impact Development (LID)?

The Environmental Protection Agency (EPA) defines Low-Impact Development as systems and practices that use or mimic natural processes that result in the infiltration, evapotranspiration, or use of stormwater to protect water quality and associated aquatic habitat. Why does this matter? As EPA notes, applied on a broad scale, LID can maintain or restore a watershed’s hydrologic and ecological functions.

Implementing LID practices allows the treatment of stormwater closer to the source using natural processes. Closer to the source means treating the water as close to where it reaches the earth’s surface as possible.  For example, stormwater that sheet flows off a roadway and is collected in a swale then treated by an LID practice is treating the water closer to the source than if the stormwater were collected in a closed drainage system within the roadway and conveyed several hundred feet away to a larger detention pond.  The swale (known as a level spreader) acts as a level swale that collects the stormwater and infiltrates it slowly into the ground, similar to what the water would do if the paved roadway were not present. For more significant flows that overtop the level spreader, a best management practice can provide some treatment of common pollutants, including total phosphorus (TP), total nitrogen (TN), and total suspended solids (TSS) (gravels in the stormwater) before the stormwater reaches a waterbody. 

Best Management Practices (BMPs) are defined as methods that have been determined to be the most effective and practical means of preventing or reducing non-point source pollution to help achieve water quality goals. Non-point source pollution includes TP, TN, and TSS.  Some BMP’s commonly used include bioretention facilities, rain gardens, vegetated rooftops, and tree box filters. Methods used to treat the stormwater include infiltration, filtration, detention, retention, and disconnection.  Infiltration and filtration are similar in the way the water flows through a media which provides the treatment.  The media used in infiltration practices it the natural soils which then convey the stormwater to the groundwater below. In filtration systems, the media is a man-made media, sometimes consisting of sand, sometimes a combination of sand/soil/and compost mixture, and sometimes a manufactured filter similar to filters you find in your house or car.  Detention and retention are similar methods, they detain water. Detention practices detain water for a short time while retention practices typically have standing water at all times. Both treat the stormwater by allowing pollutants to settle out of the water over time. Disconnection methods includes conveying stormwater from an impervious surface (rooftop or pavement) to a pervious surface (grass) to allow the stormwater to naturally filter through the grass and into the soils prior to reaching surface water or groundwater sources.

Protecting our Watershed with These Methods

So how do BMPs or LID practices help with flooding or protecting the watershed?

One way these methods protect our watersheds are through the filtration.  A rain garden is designed as a small depression in the ground that consists of various native plants planted on top of a filter media.  The filter media allows the stormwater to be conveyed through it and also allows for uptake of the stormwater through the roots of the plants providing treatment of the stormwater and evapotranspiration of the stormwater (release of water to the atmosphere from soil and plant leaves).  Stormwater that filters through the media can either infiltrate into the groundwater if the soils are conducive to that, or the treated stormwater can be collected in a pipe and conveyed to nearby surface waters.  Treating the stormwater is important because untreated stormwater that reaches a waterbody (wetland, stream, pond) can affect the plant and animal life in that waterbody.  This can lead to the degradation of ecosystems across the watershed.

A construction photo of underground storage chambers for flood control at Manchester-Boston Regional Airport.

Another way we can protect the watershed using LID is through flood control. Underground storage chambers can be used as flood control in areas where there is limited above-ground storage. These best management practices are common in urban developments, including shopping centers and stadiums.  They are commonly placed beneath parking lots (such as this one pictured above, at Manchester-Boston Regional Airport) and act as a large storage facility for stormwater which can then be released at a controlled rate to nearby surface waters or infiltrated into the groundwater.

This photo shows the park where an underground storage system will be provided. The usability and aesthetics of the park will remain the same as existing conditions after construction.

Our Recent Drainage Projects

In Massachusetts, we are working on two projects that are the same roadway and therefore have similar properties, although they are in two different towns.  A large portion of these projects is within a water supply reservoir watershed.  Its location means that treating the stormwater runoff is critical so that any contaminants in the runoff do not compromise the clean water in the reservoir. Massachusetts stormwater regulations are geared toward treating the stormwater at the source as opposed to collecting large volumes of stormwater and treating it in a larger detention basin somewhere down the road.  To achieve compliance with the regulations and treat the stormwater, we have designed LID practices such as forebays, level spreaders, and grass swales at as many outlet pipe locations (outfalls) as allowable based on site constraints, including right-of-way and topography. 

Sample engineering plan and section for sustainable drainage methods.

A town in Vermont is having erosion issues at the base of a steep, dead-end, gravel road.  The erosion issues are due to the lack of stormwater conveyance practices and the lack of storage of more significant storm events.  This section of town is upstream from a large wetland, however it is not hydrologically connected to it, which means stormwater does not directly get conveyed to the wetland.  We were tasked by the regional planning commission to design two stormwater treatment practices that would convey the stormwater to the wetland area without creating additional erosion or flood control issues downstream. Both treatment practices included underground storage chambers for flood control of the larger storm events.  More formal ditch lines and a closed drainage system were designed to collect the stormwater that currently flows over the gravel roadway. 

This photo shows the location of a proposed underground storage facility for stormwater with an above-ground rain garden. In the bottom right corner of this photo, there is an existing rain garden that will be expanded.

The upstream BMP was designed to infiltrate the smaller storms.  It was requested this BMP not permanently impact the adjacent Town Green area; therefore with the underground chambers, the BMP will not be visible from above, thus not impacting the character of the Town Green.  It was requested the downstream BMP include a bioretention area (or rain garden) above the underground storage chambers.  The town requested a more natural stormwater collection process and liked the visual aspect of what a rain garden offered.  The soils beneath this BMP were not conducive to infiltration, therefore the flow out of the storage chambers was conveyed toward the downstream wetland via a pipe.

Sustainable Drainage Systems are everywhere – you have probably seen them and not even known it!  Take a look around next time you are out and about and see what you can find. For more information about sustainable drainage, reach out to me!

Celebrating Walkability in the Month of April with Pedestrian Bridges

Mine Falls Park Bridge

The month of April holds some significant dates for the environment. The month kicks off with National Walk to Work Day on April 2nd, National Walking Day on April 7th, and we round out the month with Earth Day on April 22nd. In honor of our environment, we wanted to highlight a couple of our recent pedestrian bridge projects that encourage more foot and less vehicle traffic.

The Eaton Street pedestrian bridge was built in 1912 as part of the Boston and Maine Railroad. In the 1990s, the City of Nashua repurposed the abandoned railroad into a recreation path called the Heritage Rail Trail. This trail connects the Tree Streets Neighborhood to downtown Nashua and its many restaurants, small businesses, and cultural landmarks. The City closed the bridge to pedestrian traffic in December 2019 due to timber deck and old railroad ties rot. Hoyle, Tanner completed a full structural inspection of the bridge and provided repair recommendations to the City so that the bridge could be re-opened; we also made maintenance recommendations so that the bridge can remain in usable condition for years to come.

Mine Falls Park Bridge

To the north of the Heritage Rail Trail and in the center of the City is the 325 acre Mine Falls Park. The City of Nashua received NHDOT Transportation Alterative Program (TAP) funding to build a pedestrian link between Mine Falls Park and the Heritage Rail Trail. This project included many different design features in a small area such as an ADA complaint ramp system, a shared use shoulder along Everett Street, a crosswalk with flashing beacons at Ledge Street, and a prefabricated metal pedestrian truss bridge to cross the Nashua Canal. The crux of the project was to find a way to support the new bridge that would not increase or change the loading on the canal’s southern stone wall or northern earth embankment. To do this, we chose to use helical piles which transfer the bridge load into the ground below the canal. Helical piles have many advantages in urban locations because they can be installed with small construction equipment and with minimal ground vibration. The completed project was open to the public in June 2019.

Part of creating sustainable infrastructure is considering how people will use that infrastructure for years to come. The bridges we design must not only stand the test of time, but they must serve the community, as well as encourage more walkable and rideable communities!

Celebrating St. Patrick’s Day with a Focus on Green (Infrastructure)

Stormwater Detention Pond Construction

To celebrate St. Patrick’s Day this year, we wanted to highlight some the ways we embrace green infrastructure. Sometimes our projects are naturally geared towards sustainability out of necessity (i.e. so we don’t disturb wildlife or certain plant species), while other projects may not have a need for sustainability but we see a way to incorporate it (i.e. better stormwater management).

Before we get into some of the specific green infrastructure examples, it is important to establish some background. First, green infrastructure is not just a marketing term; it is defined by the US Environmental Protection Agency (EPA) as “the range of measures that use plant or soil systems, permeable pavement or other permeable surfaces or substrates, stormwater harvest and reuse, or landscaping to store, infiltrate, or evapotranspirate stormwater and reduce flows to sewer systems or to surface waters.”

In other words, green infrastructure is using natural means to move water rather than building more infrastructure like pipes or drains. These projects are highlights of our recent green stormwater infrastructure.

Green Methodology

As part of a consultant team, we have developed a methodology for the Vermont Department of Environmental Conservation (VTDEC) to prepare cost estimates for the implementation, and operation and maintenance of stormwater projects for all land use sectors (agricultural, wetlands, river/streams, lakeshore, forest roads/trails, roads, urban, etc.), as well as developed an O&M standards manual for continued operation of these practices. The final product was recently submitted to the State of Vermont and will outline how stormwater projects are planned, implemented and maintained throughout the State.

Green Bioretention

Bioretention

One project I worked on was to conduct an Engineering Feasibility Analysis for the City of South Burlington Municipal Office complex which had been identified as a location to evaluate and implement stormwater management improvements. The analysis resulted in the implementation of Low Impact Development (LID) measures. The designed stormwater management improvements included a bioretention facility, vegetated swale, and underground storage system.

The bioretention facility works to collect and absorb runoff from rooftops, sidewalks, and paved surfaces.  Bioretention practices mimic natural hydrology by infiltrating and evaporating and transpiring stormwater runoff.

Green Gravel Wetlands

This project addressed collected stormwater flowing into Bartlett Brook, crossing beneath Route 7 and ultimately into Shelburne Bay in Vermont. The design concept that had been developed by others through the Bartlett Brook Flow Restoration Plan process included capturing collected stormwater runoff from the neighborhood and conveying this stormwater to a City-owned parcel on the west and downgradient side of the neighborhood to allow for underground infiltration. Upon further investigation, site soil conditions were found to be unfavorable for stormwater infiltration. As a result, the Hoyle, Tanner Team designed a gravel wetland at the City-owned site to provide for flow detention and phosphorus removal of the collected stormwater runoff from the contributing residential drainage area.

Green Plans

Finally, but not least in importance, is planning for green infrastructure’s future. As part of a large integrated water quality planning effort for the City of Burlington, green stormwater infrastructure (GSI) projects were included as an important means to reduce stormwater flows and phosphorus loading to the combined sewer system in Burlington.

As part of meeting requirements for different Clean Water Act programs, Burlington’s Integrated Plan is intended to identify and prioritize water quality opportunities that result in a cost-effective program to achieve water quality goals. Tasks included the development of a comprehensive clean water alternatives analysis, including identification of enhanced phosphorus optimization at wastewater treatment facilities; identification of City-wide runoff (stormwater and wet-weather) opportunities; planning concepts for high-priority runoff mitigation projects; financial capability analysis; facilitation of public outreach; and development of an Integrated Plan with an implementation schedule. Burlington’s Integrated Plan development is currently in progress with an anticipated submission to State regulators later this year.

Stormwater runoff is a major cause of water pollution in urban areas, carrying trash, bacteria, phosphorus, and other pollutants from the urban landscape into our waterways.  Implementation of green infrastructure can help mitigate stormwater runoff by providing natural areas within the urban landscape that provide habitat, flood protection, and cleaner water. At Hoyle, Tanner, we look for ways to incorporate green infrastructure into our planning and design concepts to maximize the environmental benefits they can provide.

Part 2: Six Programs that Contribute to a 2D Hydraulic Model & Why They Matter

Hydraulic modeling software image with arrows and blue green and orange colors showing water movement

We introduced 2D hydraulic modeling and its purpose in Part I as a way to calculate how water moves and why we use the modeling to help us engineer better bridges. With that understanding, we can further explain the different ways we get the data to make those 2D models work.

The math and programming are not simple, so using simplified terms, we will break down six common programs and types of data to show how it all comes together.

#1: Google Earth

Google Earth: Many people know Google Earth as a fun tool to see their house or maybe where they want to vacation either in an aerial or street view. Engineers use Google Earth not only to see existing conditions, but also to see the aerial history of a location, as Google has images of the land as it has changed over time. For example, we can use Google Earth to look at a river 20 years ago and see how that same location has changed over that period! Is it wider because the banks are eroding? Has it meandered, causing our bridge to need re-alignment to better fit the path it has taken? Has it taken a shortcut and cutoff any oxbows (or U-shaped bends in the river) over time?

Google Earth graphic showing how the land can change over time. This image shows oxbows cut off over time (change of 22 years shown from 1996 to 2018).



The aerial images also provide information as to the roughness (think texture) or the topography. When the river floods, will the water pass quickly over the smooth fields, or will it slow down because it has to travel through a dense forest with brush scattered over the forest floor? We apply a Manning’s roughness coefficient, n, to this area in the water modeling software to help it figure out where the water wants to move. The street view can help show what the surrounding area is like from the ground to give a better idea of what the roughness should be. Sometimes it is challenging to determine how dense a forest is from the aerial view, but the street view could show if the forest floor is clean with few branches at water level, or if there’s a lot of low branches and additional brush that will slow the water down in the event of a flood.

#2: StreamStats

StreamStats: StreamStats is a web-based geographic information system (GIS) application for water-resources planning that we use to delineate watersheds and determine flow (or how much water is passing through a section). This application uses gage data of existing streams and known flows with regression equations to determine the flood flows at a location without a gage. Now first off, you might be asking yourself “what the heck is a gage?” A streamgage uses instruments to measure and record how much water is flowing in a stream at a particular location. You can learn more about it on the US Geological Survey (USGS) website. Secondly, you might be thinking “what is a regression equation?” This is a type of equation used in statistics to determine a parameter (e.g. flow) based on the relationship between sets of data like watershed size and storage. Essentially, the equations use the information from streams with gages to extrapolate what the flow most likely is at an ungaged site. You can click on a stream point (as long as it’s inside applicable limits) and the program will then delineate the watershed and tell you what your flow is! But as is true with most software, you need to check what it gives you to make sure the delineated watershed is accurate, and the flows are reasonable.

#3: Mathcad

Mathcad: We use Mathcad to perform calculations. For example, New Hampshire requires engineers to complete hydrology calculations for bridge designs; alternative methods to determine the flood flows at the bridge are done to check that the flows determined by StreamStats are reasonable. Again, it’s not as straightforward as “StreamStats is giving me this data, let’s use it,” it needs to be checked! Mathcad allows us to efficiently check the flows from StreamStats by using other methods (i.e. equations). Mathcad is also commonly used to calculate the scour depths around the bridge foundations and size the riprap protection mentioned in Part I.

#4: LiDAR

LiDAR: We also use LiDAR data. While not a specific program, LiDAR gives us images from ground penetrating radar so that we can bring these images into a hydraulic model to merge with survey data. From this information, we can get a fairly accurate account of land to model. LiDAR will reflect things like a knoll in a plane underwater, but it won’t show the water itself; it will show why the water is moving around something we can’t see without this data.

#5: SMS

Surface-water Modeling Solution: More commonly known as SMS, this program is the graphical user interface developed by Aquaveo; this is the software that we use to put together all of the data to create a model that can showcase contours and streamlines representing water. We use the aerial image from Google Earth in the program to define the various areas of terrain roughness; use the flows from StreamStats to tell the program how much water it needs to include; and use the LiDAR to define the topography throughout the model. SMS is especially useful when we are explaining to clients the need for different types of infrastructure or to show the public what’s going on with the water, but it’s also useful for the engineers to be able to see the reason we would need different foundations for a bridge or different materials to construct with because of water flow. For example, although the bridge may span the bankfull width, is the bridge still a constriction in the overall floodplain that could cause deep scour? Or is there an area of the roadway that is still overtopping and might experience erosion?

#6: SRH-2D

Sedimentation and River Hydraulics – Two-Dimensional model: This program is known as SRH-2D and was developed at the US Bureau of Reclamation in collaboration with the Federal Highway Administration and the Water Resources Agency in Taiwan. This is the software that deals with the computational efforts that go on behind the scenes after the model is built in SMS. It’s a 2D hydraulic, sediment, temperature and vegetation model for river systems. SMS and SRH-2D usually confuse people because they think they are the same, but you use each of them for different purposes: SMS is for setup and reviewing results, and SRH-2D is for processing for the information.

There are some programs we haven’t talked about here. For simple culverts, the HY-8 Culvert Analysis Program developed by the Federal Highway Administration may be used. SRH-2D can utilize HY-8 to incorporate culverts within the 2D model; this development of SRH-2D was in cooperation with Aquaveo and the Environmental Modeling Research Laboratory at Brigham Young University. For 1D hydraulic modeling we would use the Hydrologic Engineering Center’s River Analysis System (HEC-RAS) developed by the US Army Corps of Engineers – which can be used for 2D but is not as widely used as SMS, especially in the Northeast. We could also use 3D hydraulic modeling technology, such as FLOW-3D, but that will be more prevalent in the future when computational power can better handle the programs required for it.

Computers have come a long way in being able to process the complicated software to create 2D hydraulic models. While 1D hydraulic modeling gave us more capabilities with bridge hydraulics than just calculators, we are pleased with the extra capabilities 2D hydraulic modeling has afforded us and are always looking for ways to use it better. Want to find out more about 2D hydraulic modeling?

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!

From Groundbreaking to Ribbon Cutting: An Internship with Hoyle, Tanner

Over the past three months, I have had the pleasure of being part of the Hoyle, Tanner team, primarily in the Bridges & Structures group. I have gotten to see and experience a variety of different projects at all stages, and I am grateful for this opportunity and everything I learned along the way.

Projects in Derry

The first half of my internship experience was spent in Derry, New Hampshire replacing a bridge with structurally deficient culverts on this box culvert project. Here I performed Resident Project Representative (RPR) services and observed construction from start to finish – when the excavator broke ground to when the bridge was reopened to traffic. It was very rewarding to see the full project life-cycle and be there to walk the bridge. Every day in the field there was a new step and process for me to learn and see for the first time. Being on site opened my eyes to how many people are involved in the entirety of a project. Now I better understand the client, contractor, and engineer’s roles in making a project successful. For example, Hoyle, Tanner, the contractor, and the Town worked together to make field changes as needed.

Working on this project also introduced me to new engineering computer programs such as Bluebeam, MicroStation, and Mathcad that allowed me to edit drawings, review check sets and create other engineering documents. User efficiency greatly improved from the first days of using a program compared to after a couple of months.

Projects in Bedford

The last half of my internship has been spent in Bedford, New Hampshire where I took on day-to-day inspections of a gas main project. My duty there was to make sure the trench is properly backfilled and compacted and make sure everything goes according to plan. This role was rewarding because it allowed me to work more independently. I frequently communicated with the client on day-to-day progress and was the bridge of communication to the site.

At Hoyle, Tanner I was welcomed with open arms (virtually) and felt like I belonged. I am thankful my supervisor emphasized spending as much time in the field as I could because the experience taught me valuable lessons. I enjoyed the team environment and how my questions were encouraged by everyone. This opportunity brought me new experience and knowledge, and has increased my interest in field work. I’d like to personally thank Matthew Low, PE for providing me with this opportunity, Josif Bicja, PE for showing me what it takes to be a great engineer, and Katie Welch, EIT for guiding me along the way.

Derry, NH Box Culvert Replacement Project

A New Technology for Covered Bridge Inspections

Drone image of Kingsley Covered Bridge

The Unsung Beauty of Covered Bridges

Covered bridges, to me, were the quintessential structures of the 19th century, and to this day, can still inspire awe. These are bridges that were often built from trees cut locally, hand-hewn, brought to the site by livestock and assembled without modern machinery. When completed, you have a sort of house of cards; a wooden plank deck spanning a stream or raging river, walls reaching up from its sides containing many vertical and diagonal wooden members, a roof covering the expanse containing even more diagonal members, all held together with mortise and tenon joints and wooden pegs. This is a mongrel of bridge construction that has a beauty to it like no other, blending in with its surroundings as if it were always there, the backdrop for postcards, calendars and many personal moments shared between friends and loved ones. Sadly, most of these bridges have gone into the pages of history – neglected beyond repair, victims of mother nature, casualties of vandals, replaced with modern structures or simply forgotten. Those that still exist are revered and protected passionately by those who still believe in their relevance and their beauty. They do however require regular inspections and maintenance to ensure they can meet the needs of the communities they serve.

Those that still exist are revered and protected passionately by those who still believe in their relevance and their beauty. They do however require regular inspections and maintenance to ensure they can meet the needs of the communities they serve.

Inspections are Challenging for these Structures

Over the years, I have had the awesome opportunity to inspect many of these beautiful works of craftsmanship. These inspections are laborious in nature, requiring multiple days for a thorough inspection, getting covered in dirt and dust from crawling around the hard-to-reach spaces. It’s vital to know the size and condition of as many members as can be seen and reached, recording all that is found – dimensional losses, an array of structural deficiencies including but not limited to cracks, splits, checks, insect infestation and rot to name a few. The tape measure, extension ladder, headlamp and digital camera are tools of the trade. But what about inspecting the places that are more difficult or impossible to get to because of the length and height of these structures or the geography they span?  Simply put, you get what you can, as good as you can, and the rest is filled in with existing plans and many, many digital photos. The camera is your best friend when inspecting and is an invaluable resource. But even so, photos can be deceiving – awkward angles, poor lighting and size distortion, cause confusion as to what is truly being captured. As for inspecting floor systems, getting underneath is the only way to go, either by rigging, rope climbing or even by boat if the height above the water makes it feasible.

When the Standard Inspection Options Aren’t Adequate

Recently I traveled to Clarendon, Vermont with Josif Bicja, PE to inspect the Kingsley Covered Bridge for a scoping report to determine the feasibility of multiple rehabilitation options. This is an historic 119-foot-long, single span, town lattice bridge spanning the Mill River flowing 35 feet below. The Kingsley Covered Bridge poses the same issues as any other covered bridge inspection, but in addition, because of the height above the stream, it makes it difficult if not impossible to get a good visual of the floor system and siding. A rigging company could have been hired to provide access to inspect the floor system through the use of bridge trackers or bucket boats which will get you up close to get that good visual, or the bridge could have been climbed, but these options are not economically feasible for a scoping study. The options you are left with is to don a pair of waders, carefully walk out into the water with your clipboard and camera and capture what you can. If the water is not passable, you stand on the shore and do your best to get the information you need.

There is a better way. The drone. Those sci-fi looking machines, with their distinguishable propeller sound that are used widely in law enforcement, the military and with private enthusiasts alike, have been making their way into other useful applications. Over the past few years, engineering companies like Hoyle, Tanner have seen the value of drones for public relations documents, project marketing, 3D visualizations, traffic studies, and now bridge inspections. The height of this bridge over the Mill River made it a perfect candidate to fly a drone and test its capabilities in this capacity. Drones have safety features that will not allow them to fly close to aerial obstructions, like trees and overhead utilities, or fly in strong winds such as updrafts under a bridge, which are both prevalent at this site. The safety features would have to be turned off for the drone to perform its inspection well, which meant that the steady hand of an experienced pilot would be essential.

For the underside of the bridge, it flew a few feet from the structure providing the ability to clearly see the members that make up the floor framing, including joint locations and condition. Then the drone was flown along the sides of the bridge and along the roofline, capturing a similar up-close visual of the vertical siding and metal roof conditions that we normally would not have been able to see.

Patrick Sharrow, AAE from our Burlington, Vermont office drove down and met us on-site on the morning of our second day inspecting the bridge. It took Patrick just a few moments to familiarize himself with the structure and geography of the site, understand what we needed the drone to capture and determine the best launching spots for the drone. Looking at the handheld monitor, Josif was able to give instructions as to where he needed the drone to fly,  while I acted as spotter to make sure the drone kept a safe distance from any aerial obstructions and Patrick executed the flight. For the underside of the bridge, it flew a few feet from the structure providing the ability to clearly see the members that make up the floor framing, including joint locations and condition. Then the drone was flown along the sides of the bridge and along the roofline, capturing a similar up-close visual of the vertical siding and metal roof conditions that we normally would not have been able to see. The videos captured of these hard-to-get-to portions of this bridge will allow for better recommendations for the multiple rehabilitation options, leading to more accurate costs for the client. We then took the drone to a higher elevation and flew a few hundred feet upstream down towards the bridge, giving a bird’s eye view of Mill Stream. Patrick flew it at different elevations and angles capturing fantastic footage of the morphology of the stream and a greater scope of how this bridge is situated on the site. Portions of these videos could be used in public information meetings to help educate the public and as tools for Hoyle, Tanner.

Day-to-Day Needs of the Community Combined with Aesthetic Nostalgia

In less than an hour, we were able to gather more information about this structure than we would have been able to because of the site restrictions this bridge poses. The best part is that all players in the game benefit from this. The design team will have the ability to make more accurate rehabilitation recommendations. The client will have the advantage of receiving more accurate cost estimates for each rehabilitation option. The public will receive the best rehabilitated structure option, marrying together the day-to-day needs of the community and the aesthetic nostalgia it provides to all.

At-The-Ready Consultant Services: A Streamlined Approach to Starting Your Project

If your community was awarded a grant through the Vermont Agency of Transportation (VTrans) Municipal Assistance Bureau (MAB), you can take advantage of a streamlined approach to procuring your project consultant through the At-The-Ready (ATR) process. With this choice, municipalities have an alternative option to the standard RFQ/RFP process; an option that can speed up your proposed project schedule using prequalified and reputable experts in their field with success in delivering projects in accordance with VTrans MAB standards. VTrans maintains ATR consultants from a qualified roster, ready for qualifications-based-selection (QBS) when a project arises.

This accelerated procurement method can be applied to three categories of work:

  1. Design (including Scoping)
  2. Municipal Project Management
  3. Construction Inspection

If the ATR process is something your community would like to consider, VTrans has set up a simple Guide and Flowchart that can be followed and coordinated with your VTrans Project Supervisor. Begin by defining a selection committee (minimum of two members); along with the Municipal Representative in Responsible Charge (typical members could include the Municipal Project Manager, Public Works Engineer, Road Foreman or other municipal representatives). The committee then reviews a minimum of three consultant qualifications packages and selects the firm that best meets the needs of the municipality for the particular project. Once the committee chooses a firm, they can work through the cost proposal process with the VTrans Project Supervisor and the consultant.

For a municipality, the ATR process is beneficial for more than just accelerating the procurement of consultant services. Utilizing ATR also ensures you will be selecting from qualified firms that are experts in completing MAB funded projects. Instead of preparing a laborious Request for Qualifications package and then reviewing multiple submissions, the QBS selection is made easier, giving the option of only a minimum of three to pick from, while maintaining full state and federal grant/funding eligibility.

Hoyle, Tanner has had a working relationship with the VTrans MAB group for over 20 years and has been an ATR Consultant under the Design Category since the program began in 2017. We are a prequalified Design Consultant and are At-the-Ready whenever a municipality needs.

If you have any questions about the ATR process, contact Jon Olin, PE, our Vice President and Regional Business Manager of our Vermont office.

What you May not Have Considered about Solar Energy in New England

Hoyle, Tanner is currently providing professional engineering design services for the development of solar energy in New England. We are working for several solar companies as the solar industry has not only taken off in the flatlands of our Midwest United States, but solar energy development is also happening in our New England backyards.

There are many reasons why this industry has recently become so popular. Solar energy has become a viable option because of the sun’s power – but also because of its cost. As the technology of solar energy has become more efficient, the option for purchasing solar power has become a reality to an average energy user.

In order to consider solar options, permitting and procurement need to be considered.

Permitting

Public utilities commissions and state regulators have recently developed and revised rules and regulations for the advancement of solar energy. Hoyle, Tanner has stayed up-to-date with the development of these guidelines so that we can keep our clients educated and able to make sound decisions and reliable investments — not only based on costs, but also permitting success. The probability of getting a project permitted is a major milestone in the progression of a project, and can in many cases can determine if the project ever gets started.

There are many factors that contribute to the permitting and design of a solar array. Following is a list of some major factors that can affect development:

  • What is the size and shape of the property?
  • Is the property located in a properly zoned area or can it be rezoned?
  • Are the soils adequate to develop for this use? Are there significant wetlands? Are they well drained soils?
  • Is the topography adequate for solar development? Is the orientation of the property favorable for solar development?
  • Are there abutting structures on neighboring property that would prevent sunlight from reaching the site?
  • Is there adequate access to the property?
  • Is there access to an existing power source to transmit the power?
  • Are there natural resource protection areas within the site (vernal pools, deer wintering areas, or historic preservation areas)?
  • Does the developer have adequate title to the property?

Hoyle, Tanner has developed several solar array sites being cognizant of all the factors pertaining to a successfully designed and permitted project, while keeping versed of the regulatory processes. With our experience, we can save the client time and money while helping them realize a successful project.

Procurement

In many state governments, there is a procurement process for renewable energy projects (that are part of energy packages). These packages contain guidelines for the development of a limited amount of energy. What we are finding in some states is the need to increase the development limits as demand increases. Hoyle, Tanner is working with state agencies to make sure we are aware of these opportunities so that we may share them with our clients.

In some states there is a procurement process, raising the net metering cap, allowing arrays of up to 5MW — 5,000 KW — to sell or store excess energy. 

Raising the cap is what makes renewable energy development viable for investors, developers, and municipalities. These opportunities to create renewable energy not only lower the states’ dependence on fossil fuels to generate electricity but are also expected to create new jobs in the coming years as the number of projects increase.

Many states look to increase their renewable energy portfolio standard — the amount of renewable electricity created as opposed to that created by fossil fuels — from lows currently at 10% or less to 40% or 80% by 2030 and some even at 100% by 2050.

Helping Developers

We understand the importance of this type of development and the need for development of renewable resources. Our design experience helps the developers understand the limitations of development and of course the permitting process.

Hoyle, Tanner’s experts are here to help. If you have any solar development questions, contact Andy Sturgeon, Vice President and Regional Business Manager.

Landslides: Prevention & Repair Through Slope Stabilization

Slope failure photo with blog title

In New England, March marks the last weeks of winter and the start of spring rains and snow melt.  Paying attention to erosion control during this time of year is always on the minds of municipal public works staff, state agencies, construction companies, and even homeowners, especially those fortunate enough (or perhaps not) to have water frontage. 

A 2018 study conducted by the USDA found that precipitation is increasing in the northeast more than any other region in the United States. The frequency of consecutive wet days is generally increasing in the northeast and precipitation extremes have also become more frequent. Given these trends, it is no surprise that peak flows in rivers and streams are also increasing and occurring earlier in the year which can result in a greater risk of flooding.

While it is difficult to prevent major erosion of stream and river banks due to extreme precipitation events, damage can be mitigated by inspections of at-risk areas combined with prioritization of these areas for repair. It is important to address slope failures quickly because bank degradation can cause significant damage including loss of property and infrastructure, sedimentation of the waterbody, water quality issues and damage to critical riparian buffer areas. As civil engineers, we can provide assistance with erosion control issues that range from preventative design practices, culvert replacements and stabilization of failed embankments.

Below is a list of some stabilization practices along with before and after photos of our recent embankment stabilization projects.

One such embankment failure occurred in Lancaster, New Hampshire, when high flow conditions in the Connecticut River resulted in severe washouts along an 800 foot long embankment causing loss of land and unstable soil conditions. Hoyle, Tanner designed and permitted solutions to repair and stabilize the slope using native riparian vegetation and rip rap armament. Live willow and dogwood stakes were planted in soil between the rip rap stones.

Terms to know:

  • Live willow & dogwood stakes: Living shrub cuttings that take root quickly in bank environments – provides natural habitat and additional erosion control
  • Rip rap: Large stones used for protection and dissipation of energy from high water flows
Washout along the Connecticut River in Lancaster
Lancaster Embankment after Stabilization

Hoyle, Tanner also designed and permitted repairs to a steep slope in Rochester, Vermont, when intense rainfall events undermined the toe of the bank, causing the slope and roadway above to fail and slide into Brandon Brook 90 feet below.  The repair solutions included installation of a blast rock toe detail and stone facing with grubbing material along the hillside to restore the slope. The roadway was reconstructed and a mid-slope underdrain was installed to intercept groundwater seepage. Debris from the slope failure was removed from Brandon Brook and the streambed was restored.

Terms to know:

  • Stone facing with grubbings: Combination of stone and native material to promote vegetation growth
  • Blast rock toe: Large rocks placed at the toe of the re-stabilized slope to combat undermining
Rochester Slope Failure at Brandon Brook
Brandon Brook Stabilized Slope Repair

Improving safety and combatting damage from growing peak flows and extreme storm events is an important part of our job. Hoyle, Tanner is excited to offer solutions to slope stability issues and challenging site conditions. For more information on how we can be of assistance, please contact me.

New Changes for Designing Low-Volume Roads

While staying up-to-date on standards, manuals, guidelines, policies, and specifications can be challenging, the Hoyle, Tanner design teams have welcomed the Second Edition Guidelines for Geometric Design of Low-Volume Roads (Guidelines) recently published by the American Association of State Highway and Transportation Officials (AASHTO). The updated guidelines expand the definition of low-volume which provides greater flexibility to Hoyle, Tanner’s engineers to design the appropriate solution for the challenges our clients face. We’re going to cover some basics of the Guidelines and why it is so welcomed.

In the first edition (2001), low-volume roads were considered to have traffic volumes of 400 vehicles per day (vpd) or less. With the newest release (2019), the Guidelines expand coverage to roads with traffic volumes of 2,000 vpd or less. What does 400 vpd look like? For perspective: If you were to walk down a street, you’d expect to see one vehicle approximately every 3 ½ minutes at 400 vpd. If the same road experienced 2,000 vpd, you’d expect to see one vehicle approximately every 45 seconds.

According to the Guidelines, 80% of the roads in the U.S. are low-volume roads.

To determine if that 80% was applicable to our clients, we reviewed available traffic counts for an “average” New Hampshire town and found a conservative 70% of their road miles met the new definition of low-volume.

The Guidelines still remain focused on very low-volume roads (≤ 400 vpd) but the inclusion of roads with volumes of ≤ 2,000 vpd is greeted with open arms. This provides our design teams an additional resource on more projects; before the latest release we could not use the Guidelines on most of our projects as traffic volumes typically exceeded 400 vpd. However, a majority of past projects had traffic volumes that did not exceed 2,000 vpd.

What’s the benefit to our clients and designers

quote-from-aashto

The Guidelines apply to both new construction and evaluating existing roadways. Here are a few things designers can consider for the construction of a new low-volume road:

Reduce pavement width allocated to vehicles, narrow the road. The obvious benefit to narrower roads is reduced construction cost. Another benefit is a decrease in environmental impacts. Thinking a little bit further beyond the edge of road, the savings from a narrower road could be invested in pedestrian and bicycle accommodations.

Reduce the design speed, allowing for the use of sharper horizontal curves. This could be used to avoid or minimize impacts to environmentally sensitive areas, an excessive cut, an excessive fill, or negative impacts to abutting properties. Doing any of these could not only reduce construction costs, but also potentially speed up the construction time and reduce the environmental permitting coordination.

Reduce the stopping sight distance, allowing for the use of sharper curves. Similar to reducing the design speed, however, this provides the designer flexibility for both the horizontal and vertical (profile) alignments. This could be used to avoid or minimize impacts to environmentally sensitive areas, an excessive cut, an excessive fill, or negative impacts to abutting properties. Doing any of these could not only reduce construction costs, but also potentially speed up the construction time and reduce the environmental permitting coordination.

Reduce the clear zone, and thus reduce or eliminate guardrail. A little side note, a clear zone is an area that allows a driver to stop safely, or regain control of a vehicle that has left the roadway. Since guardrail is a roadside hazard, costly to install, and costly to maintain when impacted, being able to reduce guardrail or eliminate it reduces construction maintenance costs and potential accidents involving it.

With this increased flexibility the Guidelines provide there is still engineering judgement to be used. For instance, it would be ill-advised to combine a narrow road with sharper curves and reduced stopping sight distance. Remember the intent of the Guideline is to reduce crash frequency and severity while prudently using public funds.

infographic

What about all the existing roads to be maintained?

We have the ability to evaluate how the existing road is performing and if it meets the Guidelines. When something doesn’t meet the Guidelines, that doesn’t mean that it needs to be fixed.

For example, let’s consider a one-mile segment of low-volume rural road in good condition, and we’re looking to resurface it before it becomes worse. We go out to the site, take measurements and notes of existing conditions, and find the following:

  • The average road width is less than the Guideline recommendation.
  • There is a curve that is sharper than the Guidelines minimum radius, has no warning signs, appears multiple vehicles have left the paved surface within the curve but no reported accidents in the last 5 years.
  • There are multiple trees within the clear zone but no signs of impacts or reported accidents.

There are several ways to address each of the issues. Recalling the purpose of the Guidelines is to make improvements at locations where it can be expected to provide substantial crash reduction benefits the design team makes a recommendation. Maintain the existing road width except within the sharp curve, where the pavement is to be widened to the Guideline minimum and the trees within the clear zone are to remain.

Hoyle, Tanner’s transportation design engineers are experts in roadway design, pavement layout, roadway stormwater, and safety for vehicles and pedestrians alike. We research and commit ourselves to learning the newest design guidelines for a safer, healthier community for drivers, roadway designers, and pedestrians. Questions? Call (603) 669-5555 ext. 181 or email me to discuss the latest technology and guidelines in the transportation engineering industry.