How wet is your wetland?

In April 2020, the U.S. Environmental Protection Agency and the Department of the Army published the Navigable Waters Protection Rule in the Federal Register that finalized a revised definition of which waters are considered “jurisdictional waters” in the United States. (Read “Final Rule Continues Efforts to Rescind Federal Protection for Certain Streams, Wetlands,” Civil Engineering, March 2020, pages 12-13.) 

To help with wetlands assessment under the revised rule, the U.S. Army Corps of Engineers has developed a free tool to help users determine what a typical year of rainfall looks like at a given study site and whether that site is currently experiencing dry, normal, or wet conditions. And the North Carolina-based Swamp School, which offers courses and certifications in wetlands assessment, delineation, and design, has developed a fee-based next-generation version of the Corps’ tool.

“The need to assess wetlands in ‘normal’ conditions arose out of … climate change studies,” says Marc Seelinger, a senior professional wetland scientist and the founder, director, and lead instructor at the Swamp School. “If the conditions are too dry, then the (size of the) wetlands are underestimated. If the conditions are too wet, then they are overestimated.” 

The free software developed by the Corps, called the Antecedent Precipitation Tool, “automate(s) the climatological analysis workflows (that Corps) regulatory project managers are required to perform to comply with long-standing agency guidance as well as the new Navigable Waters Protection Rule,” explains the website for the Corps’ tool. The tool can be downloaded at: https://github.com/jDeters-Corps/Antecedent-Precipitation-Tool.

By displaying the information as a comparison, users can see if the site is in a wet, normal, or dry condition on the day of the study.

The software was created by Jason Deters, a senior project manager in the Sacramento District of the Corps’ California Delta Branch, to evaluate rainfall in small or large areas. The tool can perform its typical-year analysis at a single site using latitude, longitude, and date. It can assess a single wetland’s hydrology, or it can be scaled up to assess an entire watershed. 

The tool also automates the collection of weather data to ensure that information from the closest weather station — considering both distance and elevation — is used to assess a typical year’s weather pattern. Often when such data are collected manually, elevation is not considered. “Weather patterns vary greatly over relatively small lateral distances, especially if those distances are accompanied with large changes in elevation,” the website notes.

The new tool also does a better job of assessing the precipitation of a typical year because it compares 30-day rolling totals rather than comparing calendar months. Precipitation varies throughout each month, and “months vary in length,” the site explains, “yet we are comparing monthly totals to 30-day rolling totals.” 

The tool offers users 30 years plus one month of precipitation data and calculates 30-year and 30-day rolling totals. It then calculates the 30th and 70th percentile values for each day of the year.

Both the Corps’ and Swamp School’s tools generate a one-page PDF that shows a rainfall history graph of a given site compared with its 30-year history. The tools “display the actual rainfall at the study site against the statistical mean and deviation from the mean for both the wet and dry conditions,” explains Seelinger. “The wet condition is defined by having 30% more rainfall than the mean, and the dry condition is 30% less than the mean.” By displaying the information as a comparison, users can see if the site is in a wet, normal, or dry condition on the day of the study.

While the Corps tool is free to use, it has limitations that the Swamp School has worked to rectify in its proprietary system. Cybersecurity was one concern, Seelinger says. “The Corps version requires that beta software be installed on a PC. Very few engineering company IT departments would allow this.” 

Additionally, “the software is only available on GitHub, which does not vet software for security risks,” Seelinger says. GitHub is a code-hosting platform for version control and collaboration. Furthermore, Seelinger says, “Once the software is installed, the user must allow it unrestricted (file transfer protocol) access to a number of government servers. This is another cybersecurity red flag.”

The Corps version also works only on Windows computers, requires a very fast internet connection due to the volume of data it transfers, and is not accessible from mobile devices. The Swamp School system, on the other hand, is cloud-based, so while it does not require software to be downloaded and installed, it does require an active internet connection to access the web portal. 

It can work on both PC and Mac devices, and any internet-connected device can access it. “All the heavy lifting and cybersecurity (are) done on our cloud servers,” Seelinger says. “The website the customer uses is encrypted.” 

Seelinger points out, however, that the Corps’ methodology still underlies the Swamp School’s software. “It is important to note that while we changed the software interface, we did not change the Corps’ code,” Seelinger says. “We have maintained the Corps’ copyright notice in the code, and we are very clear that this is (Corps) programming. The Corps’ software copyright allows us to use the software so long as we are clear on who developed it.”

 The Swamp School version is also limited to single wetland sites and cannot be used to assess entire watersheds — although the school is considering adding that option in a future release, Seelinger says. 

The school is also working on a mobile app that will allow users to preload weather data when they have an internet connection, and then use the app without an internet connection in the field. “This will help our customers (who) work in very remote areas where there is no cellular internet,” Seelinger says. 

This article first appeared in the July/August 2021 issue of Civil Engineering as “Is Your Wetland in a Dry or Wet Period?”