ESPM 4295 Project Background

Water in urban environments causes problems: there is often too much of it. Moving rainfall runoff away from homes, roads, and other infrastructure is expensive, and increasingly, causes damage downstream. Most large cities, towns, companies, and other groups that own large properties are re-thinking how they manage water. Many are moving way from old "pipe and pond" storm sewers, and using "soft" and "green" infrastructure to process runoff on site, through storage and infiltration, and increased plant transpiration.

There are many examples, including from the City of Portland (website here), the Minnesota Pollution Control Agency (here), and the City of St Paul (here).

Your task is to evaluate how placing common types of stormwater mitigation infrastructure will reduce runoff from the St. Paul UMN Campus, and the costs of those mitigations.

Rain Gardens are common, relatively inexpensive modifications to improve infiltration. Low, vegetated areas or created, often embedded in or adjacent to hard surfaces. Runoff is directed towards them, and captured water may infiltrate. Plants increase soil drying, thereby increasing water storage capacity, and provide other benefits.

The images below show examples, and here is a link to a short video demonstrating raingardens near the St. Paul Campus.

Pervious Pavement, either asphalt or concrete, are a second common method used to increase infiltration. Concrete aggregates or asphalt pavement may be built so that water flows through, rather than over the pavement (website here). Infiltration rates may reach that of the underlying soil, and although there is some maintenance, e.g., the pavement need be vacuumed during leaf fall to keep the pavement from clogging, these costs are relatively minor compared to savings in pipe and sewer capacity and maintenance.

Tree Canopy Interception is another tool. Trees both absorb rainfall and reduce impact velocity, and hence erosive force. Much of the annual rainfall comes in small storms, such that tree canopy can reduce total surface runoff by a quarter or more in many areas. Planting more trees, or taller, denser foliage trees (e.g., conifers vs. broadleaved species) is an relatively inexpensive way to reduce runoff

Green Roofs are another method to reduce runoff. They are relatively expensive, and must be placed on flat- or low-slope roofs, but can process substantial water, often up to two inches of rainfall.

Below-ground Storage is a final method to substantially reduce runoff. You might think of them as storage tanks without sealed sides or bottoms, and typically with gravel and then sand underneath, so large volumes of water may be stored, and slowly percolate. While the most expensive of the methods discussed here, it is also the one most appropriate for larger storage volumes were space is limited. You can't economically place these under already existing buildings, but they are commonly used under parking lots, playing fields, and low-traffic roads to store water temporarily.

Your task is this semester is to first estimate build datasets that allow you to estimate runoff under various storm intensities, and then place these stormwater mitigation structures on the landscape in a manner to eliminate runoff.

You'll start with the least expensive and invasive, and increase the number and extent of the installations. This is a common sort of planning process, as many watershed districts are requiring new large construction generate no runoff for up to a 2" storm.