Lupinus perennis production field

Stormwater: Water as a blessing, not a curse

Mar 27, 2015

This first week of spring was filled with warming temperatures overall, though a freak snowstorm blew through northern Indiana on Monday and dropped 3 inches of snow in a matter of hours.  It put a bit of a damper on our plans to start our plan of prescribed burning here at the Nursery, but we certainly welcome any form in which the water may come. Considering some of the droughts we’ve had in recent years, some additional recharge for our groundwater is well worth the inconvenience of a bit of early spring snow.

St. Joseph River in Mishawaka, IN

Water is, after all, the single most important resource we have (along with energy from the sun, of course).

Unfortunately, our society often treats water as a waste product. Urban and agricultural spaces handle water differently and for different purposes, but in the end, goals are often the same: to convey water away as quickly and efficiently as possible. This is the case for both urban storm sewer systems, as well as for agricultural tile and ditch systems. And these systems are indeed efficient. So much so, that they have the ability to strongly disrupt the historical hydrological cycles and hydrographs of the rivers, streams, and wetlands to which they are connected, and can produce a number of negative environmental impacts.

 In the next couple of posts, we’ll examine a few of the impacts of our current water management policies, and some of the available solutions that have the ability to restore natural hydrological cycles. These solutions are often referred to as “green infrastructure,” the goal of which is to retain healthy supplies of clean, usable water for our ecosystems and our communities. Naturally, native plants have enormous role to play in many aspects of green infrastructure implementation, including the front end of managing stormwater where it falls, treating diverted stormwater, and restoring native ecosystems dependent upon intact hydrological regimes.

Problem: “Flashy” Hydrographs (flooding/drawdown)

Yearly hydrograph with high flow events

When we adhere to the common “collect, convey, discharge” mentality when it comes to water, our water bodies inevitably experience enormous fluctuations in water level during the year—fluctuations that didn’t occur before industrial/contemporary water management. This has several consequences.

The first is flooding, which shouldn’t be surprising. Rather than slowly percolating into the ground, water is channeled from urban and agricultural landscapes to quickly flow into our rivers and streams. And particularly in the lower reaches of a watershed, this means increased flooding. Surprisingly, flashy hydrographs also mean increased drought and draw-down in water bodies. Rivers and streams within natural hydrological regimes aren’t predominantly fed by surface run-off, but by groundwater flows. When precipitation isn’t allowed to slowly percolate into the soil but is piped away with every event, then there is no “bank” of groundwater available to recharge the rivers and streams during the hottest/driest months of the year. 

Section of the St. Joe River in drought season

Another consequence of flashy hydrographs is  that the native plant communities in and around those water bodies, which have adapted to relatively reliable regimes of water level, temperature, and chemistry, are disrupted and replaced by more opportunistic species—often exotic invasives like Phalaris arundinacea, Typhus spp., Phragmites australis, and Lythrum salicaria. Another consequence upon native plant communities is that natural wetlands—including marshes, swamps, fens—that would have been recharged by the slow flow of groundwater percolating in from precipitation, aren’t fed with adequate water, because it has been quickly channeled and piped off downstream. These wetlands dry up, and the complex and diverse wetland plant communities that inhabit them disappear.

Solution: Permeable Surfaces and Two-Stage Ditches

perviouspaver

There are several green solutions available for reducing the “flashiness” of the flow of our nearby surface waters. In the urban landscape, where much of the ground surface is covered with pavement or asphalt, one solution is the use of permeable pavement and rain gardens. Permeable pavers are fairly self-explanatory: they include durable paving materials for roads, walkways, and other applications that allow for the infiltration of water through the material and into the underlying soil. In a typical residential setting, the percentage of area covered with impermeable surfaces can be as high as 50%. In dense urban areas it is over 90%. When precipitation exceeds the amount of water able to infiltrate through these permeable surfaces, water can be directed toward rain gardens and bioswales, where water can be retained and slowly infiltrated within depressions planted with native vegetation.

Recreation area with native swale plants

Cardno Native Plant Nursery has provided plant material for countless rain garden and bioswale projects in the past. Native plants’ roots help to facilitate water infiltration and filter pollutants form stormwater, in addition to providing beauty and habitat for plants and animals. Our Stormwater seed mix is formulated to include species that tolerate the highly fluctuating water levels, and poor water quality associated with urban stormwater.  Our Swale seed mix contains species suited to filtering pollutants from urban stormwater, and facilitating infiltration of standing water.

Elevation view of a two-stage ditch design

In agricultural settings, agricultural ditches are the primary means of surface water flow. Conventional narrowly-dug agricultural ditches often receive flashy flows of water that scour the ditchbanks and cause erosion and sedimentation. Two-stage ditches create a vegetated bench above the main ditch channel. These benches act as a small floodplain and help to widen the channel during high water events, thereby reducing the velocity of the flow. These benches help to reduce erosion and sedimentation, mitigate flooding, and provide valuable ecospace for native plants and animals.

In our next post, we’ll examine some of the water quality impacts associated with traditional stormwater management (sewage overflows, pesticides, fertilizers), and how green infrastructure developments, and ecological restoration projects using native plants can help to minimize and mitigate these impacts.