Purpose

The mulch layer of a rain garden prevents erosion, controls weeds, retains moisture, adds organic material to the soil and improves drainage. The purpose of this project is to see what, if any, benefits exist from using one type of mulch versus another.  The project is a collaborative effort with the Washington Department of Ecology and Washington State University.

Scope

Starting in the fall of 2019, stormwater will be collected during targeted rain events. During the spring/summer growing season, gardens will be monitored for weed suppression and soil moisture retention by mulch type.

Project Summary

Rain gardens are used to collect and process stormwater with known success. However, maintenance of rain gardens is a time-consuming endeavor—weeding (herbicides are not recommended) and watering (during the dry summer months years 1-3 while plants are establishing). Is there a mulch that performs better at reducing these tasks?

Timeframe/timeline

2 years starting in the fall of 2019

Parameters measured

Water quantity

Water quality

Weeding effort and plant replacement costs

Elements Included in this Project

16 rain gardens at WSU-Puyallup were retrofitted in 2017 to allow researchers to hold and collect water applied to them.

There will be four replicated rain gardens containing these types of mulch:

a. Bark mulch (fir)

b. Shredded bark mulch (cedar)

c. Arborist chips

d. No mulch—control

Purpose

A variety of permeable pavement concoctions have been installed at the IDEA school’s parking lot and bus lane. The purpose is to study these mixes side by side for desirable qualities in strength/longevity and stormwater pollutant reduction outcomes. The project is a collaborative effort with Tacoma Public Schools, Washington State Department of Ecology, Boeing, City of Tacoma Center for Urban Waters, and Washington State University.

Scope

Starting in the fall of 2019, stormwater will be collected during targeted rain events. Sections of targeted pavements have sensors tracking the durability component.

Project Summary

Permeable pavements have a proven track record of improving stormwater cleanliness, however, their durability is still a work in progress. Often, in high traffic volume areas, the pavement can start to break down, or ravel, from turning vehicle wheels. Working with Boeing, the pavement mixes at the Tacoma Idea School were created with different quantities/types of carbon fibers to study the added strength benefit.

Timeframe/timeline

2 years starting in the Fall of 2019

Parameters measured

Water quality/quantity

Pavement strength/durability

Elements Included in this Project

There are four water sampling stations:

• Porous Asphalt with carbon fibers
• Porous Asphalt without carbon fibers
• Pervious Concrete with carbon fibers
• Pervious Concrete without carbon fibers

There are temperature and strain sensors within the pavement types

Pavement Demonstration

The following brief video shows the way water behaves on both permeable and impermeable pavement types.

Purpose

Our environment is quickly losing forested areas, that work as stormwater buffers, to impermeable urbanized landscapes. Currently, there does not exist a study that provides reliable and consistent information as to the stormwater value of the native species of trees in Western Washington state. This is an issue for local managers that need to make decisions based on the value of these trees. Our goal is to provide a comprehensive dataset that can be used to argue for the long-term conservation of established native tree stands in areas facing construction.

Scope

Two areas with diverse microclimates near Olympia, WA have been outfitted with a variety of environmental sensors. These sensors are either measuring ambient climate variables or are associated with individual trees. Four species common to the pacific northwest were chosen. This includes two evergreen species douglas fir (Pseudotsuga menziesii) and western redcedar (Thuja plicata), and two deciduous species, red alder (Alnus rubra) and bigleaf maple (Acer macrophylum). Over two years, several rain events and antecedent dry periods will be targeted. Data from these events will then be evaluated in order to quantify how much precipitation, which would contribute to stormwater volumes in urban environments, is being used by these trees.

Project Summary

Planting trees in rain gardens, bioswales, and other green stormwater infrastructure is a popular best management (BMP) practice for stormwater engineers. However, stands of native trees that exist in and around urban areas face removal as cities continue to expand. By presenting the unique stormwater value of existing native trees with a data rich study we hope to show that it is possible to include the conservation of these species in highly quantitative BMP frameworks that are used to ascribe stormwater credits.

Timeframe/timeline

2 years starting in the Summer of 2019

Parameters measured

Transpiration (sap flow)

Interception (precipitation – throughfall)

Precipitation

Soil Moisture

Solar Flux and Photosynthetically Active Radiation

Wind Speed and Direction

Temperature and Relative Humidity

Elements Included in this Project

There are eight tree sampling stations. Each sampling station has at least eight trees equipped with sensors to measure transpiration via sap flow and a network of troughs with at least six rain gauges that are able to capture water penetrating tree canopies. Several soil moisture sensors to observe soil wetting, canopy sensors to measure canopy temperature and relative humidity, and weather stations to measure ambient conditions are also included.