Progressive Stormwater Management

Call it what you will, it is referred to in several different ways of late including Low Impact Development (LID), Green Infrastructure, Artful Rainwater Design (ARD), Stormwater Management Facilities and Best Management Practices (BMP) among others. All of these terms refer to the management of stormwater using any number of techniques to capture, reuse, convey, retain, filter and infiltrate water in an effort to protect the health of waterways, improve water quality for human uses and wildlife habitats, reduce burdens on municipal infrastructure and replenish groundwater.  This collection of practices is often lumped together as BMP, I have chosen to call this practice Progressive Stormwater Management (PSM).

 

Why you ask? Because the practice of water management has traditionally been, throughout centuries in fact, to move water out of the way in whatever way possible and as quickly as possible to prevent, or at least, minimize the potential damage that can be brought about by stormwater.  These would include damage and destruction of living environments, soil erosion, loss of property, degradation of fish and wildlife habitats and pollution of drinking water.  Rather than treating it as an asset to be respected, stormwater has been treated as a waste product to be dealt. However, recent studies on the effects of traditional practices on groundwater supply, urban infrastructure, natural habitats and financial costs has turned attention toward understanding how a shift in stormwater management practices can relieve stresses and enhance our environment through implementing practices that seek to mimic the natural processes that would occur had development not occurred. This is very progressive thinking! Hence, my term – Progressive Stormwater Management.

 

 

Mountain Environments

The dry Mountain Environment of the western United States presents weather cycles are quite different from other regions that received precipitation more or less continuously throughout the year.  We typically experience our precipitation in the form of copious amounts of snow (in a normal year) or in flashy summer afternoon thunderstorms.  Much less likely are sustained periods of rain for more than a day or two which usually occur in the spring and fall.  In this context we have the added element of managing snowmelt as a form of ‘stormwater’.  In that the cycles of precipitation and snowmelt are typically concentrated into specific periods of time, and are not extended as in rainier climates, the challenge of compensating for flashy high volume events, present our communities and their residents with special challenges that most urban areas do not face.  Most of our terrain is sloped, often steep slopes which are more vulnerable to damage from stormwater. Add in the contaminate loads unique to snow management from road sand and deicing measures.  Couple this with typical roadway contaminates and you have the makings of what could be considered a rather complicated puzzle.

In the Lake Tahoe region the Tahoe Regional Planning Agency, (TRPA), has been in the forefront of implementing techniques to address stormwater issues and their recommended practices that have been adopted by surrounding regions.  Unfortunately, while the net effects of the program they have created have reduced the rate of degradation of Lake Tahoe’s legendary lake clarity, it has fallen sadly short of being entirely environmentally sound or sustainable.  Additionally, the BMP facilities the agency requires is heavily weighted toward Gray Infrastructure practices and misses on the opportunities that Green Infrastructure provides such as improvement and creation of habitat, recreation, education, capture and reuse of stormwater and more.  Fortunately, in recent time the TRPA has begun to recognize the value of some more Progressive Stormwater Management practices and approved their use in permitted management systems.  Following are some illustrations of alternatives to conventional practices required by TRPA and other municipalities and agencies.

 

Benefits

Progressive Stormwater Management or Green Infrastructure serves to be more aesthetically pleasing, comes much closer to mimicking natural systems, reduces strain on municipal stormwater systems and is much more economically viable.  Numerous reports express that communities that have implemented Green Infrastructure Practices save money in not only construction costs, but in long term maintenance as well. The focus here will be on the aforementioned benefits.

 

Additional benefits included energy savings for household use and stormwater treatment, reduction of greenhouse gas emissions, carbon sequestration in biomass and soil, preservation of sewer system/pipe capacity in communities where stormwater is directed to sewage treatment plants, air pollutant reductions and flood management.

 

Tools

In my practice it is my goal to help clients and communities customize a Progressive Stormwater Management Tool Box of sorts to facilitate the management of stormwater and snowmelt in ways that serve to enhance sites using highly functional, economical, safe, aesthetically pleasing and even artful means.

 

Stormwater and snowmelt management does not have to be gray, ugly, or expensive.  Following are some examples of Progressive Stormwater Management techniques.

 

First a disclaimer:  The following images are from projects throughout the country which I have borrowed off the internet.  Whenever possible I have provided the names of the designers and the photographer.  If you are one of these people and object to your work shared here, please notify me and I will remove the image promptly with my thanks for inspiring me to put these practices to work in my own practice.

 

Progressive Stormwater Management Tool Box

It is Important to note that no one tool will achieve stormwater management goals by itself, but that each site or project area will require a system of coordinated practices to fully gain the benefits of Green Infrastructure.  Following are a number of common, and not so common, tools used in Progressive Stormwater Management taken individually.  In the context of a landscape or site plan these features should be recognized and considered as parts of an overall composition integrated into the landscape to create a high functioning, sustainable and aesthetic site experience.

Artistic Conveyance

Water does not have to be the victim of underground conveyance – using creative means to move water on surfaces can help create a unique and memorable quality to spaces.

Bioretention Basins

Bioretention also known as Bio-filtration or Bio-infiltration basins are a common form of collecting stormwater for the purpose of infiltration (and filtration of contaminates as the situation warrants). Additional functions include evaporation and evapotranspiration through the planted materials found in bioretention features which take many shapes including shallow or deep basins and elongated basins (sometimes referred to as swales) and planters. Planted materials may include anything from grasses and wildflowers to trees as long as the materials are tolerant of periods of inundation and periods of drought.

Bio-swale or Water Quality Swale

Swales whether vegetated or not are intended to convey water in some way from one location to another. Bio or Water Quality Swales function to not only convey water but to detain it to allow sediment to ‘drop out’, for pollutants to be taken up by vegetation and filtered through soils. They also to slow the movement of water by detaining it for a period of time to allow high flows to subside thus reducing the potential for erosion and downstream water quality degradation. Additionally they serve a similar purpose as Bioretention features in that they allow time for infiltration, evaporation and evapotranspiration to take place. Overflow drains connected to subsurface underdrains may be added to serve to prevent long term collection of water, release excess flows to prevent flooding of adjacent sites and convey filtered excess water to alternative locations such as Constructed Wetlands.  These features may take on various levels of ornamentation depending on context.

Constructed Wetlands

Constructed Wetlands are Bio-retention features on steroids. They not only serve the purpose of bioretention but also to create habitat for water and land animals, bugs and people. Where bioretention features will commonly dry between events, Constructed Wetlands typically remain filled with water most of the year. They can vary drastically in design, scale and diversity.

Contour Infiltration Channel ©

In areas where space is limited due to site constraints Contour Infiltration Channels (CIC) can provide infiltration opportunities by creating scaled gravel filled channels that run perpendicular to the slope more or less parallel to the contours. These features direct runoff water away from foundations and impervious surfaces. In the past water has been captured by infiltration trenches directly adjacent to foundations which is no longer considered a good practice.

 

Contour Infiltration Channels may vary in width, depth and be either curved or straight to complement the architectural design. They should tie into basin low points when the low point is inside the '10’ no infiltration zone.'

 

In the second sketch the CIC is paired with a Sinuous Swale that is designed to capture rain and snowmelt from a roof dripline, direct it away from the house and infiltrate the water a safe 10’ from the foundation line. On steeper slopes the swale is broken by Water Bars or Check Dams to slow the velocity of runoff to an awaiting Bioretention Pond or Rain Garden

Flowpath Disconnection

Disconnected Flowpaths are installed where an established flowpath, such as water from a downspout that flows across the landscape, across sidewalks and into storm drain conveyances. By interrupting flowpaths with landscape features such as berms, creeks, and Rain Gardens, water is slowed, dispersed and infiltrated before it can reach the sidewalk, curb and gutter.  This reduces the potential for erosion and sediment transport while recharging groundwater and reducing burdens on the storm drain system – many of which drain into local waterways like Lake Tahoe and the Truckee River. Potential pollution of important watershed features is also reduced. In urban areas where stormwater is directed into sewage treatment plants this burden is reduced as is the potential for Combined Sewer Overflows (CSO) which lead to major contamination of local waterways.

Flow Splitter

Also known as ‘LIDA Swale’, Curb Cuts, and Overflow Splitters, Flow Splitters are streetscape and parking lot elements that capture runoff from street and curb gutters and divert it to bioretention planters, islands, basins or bio-swales where stormwater infiltrates and filters through soils to recharge ground water. In more extreme flow circumstances, excess water would be conveyed by under drains to alternative locations as the situation warrants to prevent site flooding.

Flow-through Planters or Tree Box Infiltration Planters

In urban area streetscapes, tree planters may be utilized in stormwater management systems. These usually occur on relatively level and constrained sites. They work by capturing water from roof lines and downspouts or sheet flow from sidewalks or streets to filter through conditioned soil to perforated pipes which convey the water to alternative locations for infiltration. These may be lined to protect foundations.

Green Roof

Green Roofs not only capture and retain rainwater and snowmelt, they provide insulation and cooling to the structure they cover. These provide a truly interesting and attractive visual alternative to conventional roofing systems.

Green Wall

Green Walls are a vertical garden that may be irrigated by stormwater collected by roof drainage systems and supplemented with irrigation in drier climates. Beautiful designs can be achieved using a variety of site appropriate plant materials. These, like green roofs, also provide a measure of insulation.

Habitat Creation and Improvement

When designing a PSM system there is often the opportunity to create or enhance habitat for native plants, animals, birds, insects and fish. This element is not only a benefit to potential habitat inhabitants but also a potential education piece. This project incorporates bird habitat boxes as an artistic sculptural elements into a Rain Garden.

Harvesting – Cisterns and Rain Barrels

Effective water reuse in gardens has gained in popularity recently but is an ancient practice that captures runoff from impervious surfaces such as roofs and paved surfaces and conveys it to storage containers for subsequent use in irrigating gardens and planters.

 

Rain Chains slow the velocity of free flowing water to the ground surface reducing erosion while adding an ornamental element as well.

Permeable or Pervious Paving

Cousin to the popular Concrete Paver Systems, Pervious Paving Systems look and act much like conventional concrete pavers with the added benefit of allowing water to seep between pavers to a gravel understructure and facilitate infiltration as opposed to allowing runoff from impervious surfaces to concentrate along soft surface edges, reducing potential erosion.

Public and Private Art

Progressive Stormwater Features lend themselves nicely to the infusion of artistic expression either as a functional piece of the management system or as a unique feature placed within the management system.

Rain Gardens

Rain Gardens, as with Bioretention Basins, are designed to collect, filter and infiltrate stormwater while facilitating evaporation and evapotranspiration. Generally, Rain Gardens are planted with deep rooted native and ornamental plants to create a more formal landscape composition where Bioretention Basins will typically be larger and simpler in plant palette comprising mostly grasses and maybe some wildflowers, shrubs and trees. All plant material should be able to tolerate long periods of both dry and wet times. All this with the added benefit of complementing the landscape visually.

Sinuous Swale with Contour Infiltration Channels © – 2:1 Slopes or steeper

Sinuous Swale is designed to capture rain and snowmelt from a roof dripline, direct it away from the structure and infiltrate the water a safe 10’ or more from the foundation line. The swale is broken by Water Bars or Check Dams to slow the velocity of runoff  to infiltrate in  an awaiting Bioretention Pond or Rain Garden and may be combined with Contour Infiltration Channels.

©Robie Litchfield – Litchfield Design + Consulting 2016

Soil Structure Improvement

Effective PSM requires that soil be treated with respect for the important element that it is in the function of PSM features. It is essential that compacted soils are decompacted to a functional depth, amended and revitalized as needed to ensure intended filtration and infiltration; microbial and plant habitat support and other goals are achieved. Additionally, customized soil mixes are essential for full function of LID/PSM features.

Stepped Swale – Large Space©

The Stepped Swale concept is born out of a need to comply with local jurisdictional codes that require infiltration a minimum of 10' from structural foundations while addressing stormwater management on sloped terrain.  This design is based on having the luxury of having ample space to efficiently do the work.

  1. Design is based upon a 3:1 - 2:1 slope. This system could be used on shallower slopes as well – see Sinuous Swale for application to steeper slopes.
  2. The design also assumes a wide distance between building foundation and property line
  3. Depending on required storage capacity, basins may be larger, the bottom one should be largest and may become a Rain Garden
  4. With a little imagination and space each of the basins could become a mini-rain garden
  5. Site conditions that influence the design will vary including flow volumes, soils, slopes, solar exposure, desired levels of maintenance and personal aesthetics

 

©Robie Litchfield – Litchfield Design + Consulting 2016

Stepped Swale – Limited Space ©

Stepped Swales are design to address challenges posed by steeper slopes in regions where capture and infiltration are required by local governing agencies as a rational substitute for BMP such as infiltration trenches which capture and infiltrate stormwater directly beneath roof driplines depositing water dangerously close to foundations, which has the potential for degrading the foundations during freeze-thaw cycles.

 

This concept addresses situations where structures are located directly on a 10' setback.

 

  1. Design is based upon a 3:1 - 2:1 slope. This system could be used on shallower slopes as well – see Sinuous Swale for application to steeper slopes.
  2. Depending on required storage capacity, the bottom basin should be largest and treated as a Bioretention Basin or Rain Garden
  3. With a little imagination and space each of the basins could become a mini-rain garden
  4. Site conditions that influence the design will vary including flow volumes, soils, slopes, solar exposure, desired levels of maintenance and personal aesthetics

 

©Robie Litchfield – Litchfield Design + Consulting 2016

Traditional Best Management Practices

A note about Traditional Best Management Practices, (BMP): while Traditional Best Management Practices – those that focus mainly on the use of gravel and pipe - are not preferred in Progressive Stormwater Management, they are still useful tools when space and general site logistics prohibit the use of preferred practices and should not be dismissed completely. They are best used in combination with elements of Progressive Stormwater Management.

Vegetated Filter Strips

This is a system whereby water from impervious paved surfaces is first captured and dispersed along a level bedded channel (Contour Infiltration Channel) or French Drain where the water is then allowed to move downhill through a vegetated slope to slowly allow infiltration and uptake by soil and plants before entering adjacent waterways or properties. In some instances a barrier to the waterway, such as a berm, is installed at the low end to halt the movement of large flows and allow additional infiltration time. Best results achieved by using Vegetated Filter Strips are limited to slopes that are 1-5% grade.