Thoughts From Engineers: Looking to Nature for Solutions

The city of Madison, Wis., sits within a chain of five lakes, each connected to the other in a staggered linear formation via the Yahara River, which winds roughly 42 miles through south central Wisconsin. Lake Mendota, widely viewed by freshwater scientists as “the most studied lake in the world,” is the largest in the watershed, draining a 230-square-mile watershed, 60 percent of which is in agricultural use.

Thousands of acres of wetlands surround the five lakes. Cherokee Marsh sits most upstream and filters nutrient-rich runoff from upland farm fields; further down in the watershed, Pheasant Branch Marsh is critical for the lake’s water quality as its two springs generate 2.6 million gallons daily of groundwater flow. Finally, the most downstream Waubesa Wetlands is considered a high-quality wetland, with diverse vegetation and rare plant communities.

As striking as the five lakes are, particularly from an aerial viewpoint, much like countless other cities across the country, they exemplify settlement patterns of the past that drained and filled “swampland” to accommodate the many needs of a growing city. The wetlands that remain in Dane County are therefore a fraction of what was there less than a century ago. Fortunately, growing knowledge of the benefits from these areas—from flood storage capacity to polluted runoff filtration—means the city now sees these systems of saturated soils and hydrophytic vegetation as important “infrastructure” and generally protects them as such.

In most areas, the hydrologic connection of the region’s wetlands to the lakes’ open waters is obvious; in many others, it’s not. What’s clear to the many water-resource professionals who have studied the region is that collectively the lakes and wetlands form a complex hydrological system that, among other uses, maintains the quality of the lakes as well as the integrity of the area’s groundwater, which is Madison’s primary source of drinking water. Given the variety of different types of wetlands, which includes marshes, sedge meadows, shrub/scrub, and forested wetlands and fens, the role each component plays in this complex system isn’t always obvious, but years of study have validated the integrated character of these components and the many critical interdependencies.

Templates Based on Nature

In our search for solutions to many modern urban issues, experienced professionals have increasingly adopted the mechanisms found in nature, which can work effectively under certain conditions when well-designed, monitored and managed. Bioswales, which are essentially constructed vegetated wetlands that trap and retain stormwater runoff to promote local groundwater infiltration and surface-water filtration, are an example of green infrastructure. These and similar infrastructure evolved to integrate wetland-like characteristics to replicate the functionality of the real thing. As climate change, surface-water-quality runoff and a host of other urban issues increase, these systems are increasingly integrated back into our cities, subdivisions, land-development projects and even farming to fulfill very particular regulatory requirements and local objectives.

The Nation’s Waters and Diverse Ecosystems

Studies have validated what scientists have long observed: wetlands are vital to the integrity of nearby surface waters even though they are isolated with no obvious surface-water connection. The Connectivity report, developed by the Environmental Protection Agency (EPA) in 2015 and summarizing recent research findings, distinguishes between wetlands in riparian or floodplain areas (adjacent to a waterway) and those that are outside of these areas and visibly isolated. Unlike riparian wetlands where the hydrologic connection may be clearer, isolated wetlands can be sloped or flat, depressional like prairie potholes, may lack obvious surface-water inlets or outlets, and may be fed solely by precipitation. These wetlands are nevertheless often an important source of groundwater flow.

Non-floodplain wetlands can trap nutrients, retain floodwater and support biodiverse communities even as they display different degrees of connectivity with surface water or groundwater on a seasonal, intermittent or continuous basis, and display variable biochemical and physical properties. These seemingly isolated systems nevertheless often have a cumulative impact on downstream water quality and overall ecosystem health.

What We Know

The 2023 U.S. Supreme Court case of Sackett v. Environmental Protection Agency (Sackett) held that wetlands need to have a surface-water connection to be federally protected. Before this ruling, a broader definition prevailed that included many of the aforementioned less-recognizable wetland systems: isolated wetlands, ephemeral and intermittent streams, prairie potholes, etc. No doubt implementation of the law prior to Sackett was at times arbitrary, leading to federal protections where none was warranted; but I suspect these instances were few. In most cases, site-specific findings were based on an expert’s analysis of key indicators; a sound understanding of hydrologic criteria; and other relevant biological, chemical and physical factors alluded to above.

As many recognize, an accurate identification of the systems that affect the integrity of the nation’s waters isn’t simply a matter of whether the area in question is wet/dry or whether a clear surface connection exists. We will likely lose significant wetlands, harkening back to a time when our hydrologic knowledge and understanding was weak, but we plundered on regardless, with no reason to think twice about it. The EPA projected at the time of Sackett that roughly 63 percent of currently protected wetlands would lose federal oversight.

We’ve made a lot of progress through the years in terms of what we know. We’ve gained experience in managing stormwater, particularly in heavily developed urban areas. We’ve learned about pollutants that can negatively impact water quality; we also recognize the complexity of different freshwater systems and the significant subsurface but obscure hydrologic connections that replenish groundwater and provide base flow, sustain vegetation and wildlife, and provide multiple other benefits. By sharing what we know—and equally what we don’t know—about the ecological character of wetlands on a particular project site, we’re carrying out an important responsibility to safeguard the integrity and long-term viability of the country’s many diverse waterways. 

 

Chris Maeder CivilGEO Thoughts From Engineers