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Bold Action to Protect Water Quality in Philadelphia and Beyond

April 22nd, 2010

Highlights of PennFuture’s 7th Annual Watershed Workshop

With a clear focus on Philadelphia’s remarkable new stormwater management program, including its relatively new stormwater management regulations for new/redeveloped projects as well as the revolutionary new stormwater fee rate program, PennFuture hosted a large audience at the Quaker Friends Center on Saturday April 17.  The platinum LEED Friends Center is itself testament to “new wave” stormwater thinking, with its vegetated roof, rain gardens, and runoff cistern storage/toilet recycling of captured rainwater.

Speakers included an array of leaders from the Philadelphia Water Department, including Christine Marjoram who outlined the new stormwater regulatory program and Joanne Dahme who described the stormwater fee rate program.  Dahme also detailed Philadephia’s unique Green Cities, Clean Waters effort to achieve dramatic progress in combined sewer overflow pollution reduction through “green infrastructure,” rather than the conventional gray structural systems.  Senior Attorney Brian Glass chaired the event; Pennfuture’s Rachel Vassar closed the conference with a summary of Marcellus Shale issues and challenges.

StormwaterPA’s just-released video on Philadelphia’s Green City, Clean Waters program is receiving accolades. It’ll be available soon on our Volume Two DVD (learn more about Volume One here if you haven’t seen it yet), but you can check it out here now:

Green City, Clean Waters from GreenTreks Network on Vimeo.

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Urban Stormwater Modeling Offers Room for Improvement

March 11th, 2010

As reported in last week’s blog, the March/April 2010 issue of Stormwater magazine includes several useful, provocative articles.

We wanted to offer some thoughts on several of these.

First off, let’s look at Improving the Practice of Modeling Urban Hydrology (Erik G. Peters)

From the outset, Peters acknowledges - perhaps confesses - that, although stormwater professionals would all maintain that they are committed to protection of water resources and prevention of flooding or erosion of downstream properties, we have been less than successful.  Studies demonstrate that very low levels of urban development (5% to 15% impervious surfaces) have resulted in degraded streams (Booth and Jackson 1997, Wang et al. 1997, Short et al. 2005).  Other studies indicate that the quality of our waters is still drifting downward.  What are we doing wrong?

Reducing urbanization effects on our water resources is a challenge. Many studies have confirmed that urbanization has a greater impact on frequent events than on the rare flood events (ASCE 1993). Urbanization’s effect on hydrology typically results in the following:

1.              The size of precipitation event necessary to generate runoff is lowered.

2.              There is an increase in the peak runoff rate and volume, particularly from the smaller more frequent precipitation events.

3.              There is an increase in runoff pollutant concentrations and loading (mass/surface area/time) to water bodies

Peters argues that what’s needed is to improve the current state of engineering practice - particularly urban stormwater modeling - through a better understanding of the challenges/assumptions behind the most common urban stormwater models (e.g., the Rational Method and the Curve Number or CN Method) and through providing design guidance for developing a hydrologic model using the CN Method (more specifically, developing curve numbers).  The author also argues for greater focus on Time of Concentration, “…the second most influential parameter in the CN Method, behind selection of CN values.”  Peters points out  - and this is something that’s been discussed in this Blog in past weeks (refer to the article for the referenced figures):

The CNs were originally developed to predict runoff from relatively uniform agricultural landscapes, based on research conducted largely in the eastern and midwestern US (Woodward et al. 2002). These areas of the country receive almost all of their annual precipitation in the form of rainfall. A moderately sized storm event in these regions is large enough (e.g., typical two-year, 24-hour storm event exceeds 2.5 inches or 64 mm) that CNs typically approach a constant value with rainfall depth (Figure 1). In other words, the entire watershed is contributing runoff, initial losses have been satisfied, and runoff contribution from vegetated areas is a significant contribution to the total runoff volume from a watershed. Approximately 70% of watersheds fit the pattern of Figure 1 (Hawkins 1993).

When trying to model runoff from smaller storm events or landscapes that don’t meet the above criteria, the engineer, designer, or reviewer must be more careful in the approach. When only a portion of the watershed is contributing runoff, then the CN for the overall watershed (composite CN) will vary, typically decreasing with rainfall depth as shown on the left half of Figure 1. To address this scenario, the best and most defensible method is to break up a watershed into subwatersheds of similar runoff-generating potential. This is frequently referred to as the distributed CN approach.

Peters spends a considerabe amount of time pointing out the dangers of using a weighted or composite curve number approach, arguing instead for a distributed curve number modeling approach.

There are two methods or approaches for estimating CN for watersheds having more than one hydrologic soil-cover complex. The two are commonly referred to as the composite CN and the distributed CN approach. The National Engineering Handbook, Part 630, Hydrology (NEH 630), Chapter 10, refers to the two approaches as the weighted-CN and the weighted-Q respectively.

A composite CN is an area-weighted average CN calculated for an entire watershed. In a distributed approach, polygons within a watershed are broken out based on runoff-generating potential. There is no CN averaging; rather, separate CNs are developed for each polygon and separate runoff values calculated (Grove
et al. 1998).

The most common approach is the composite CN. However, employing the distributed CN approach is necessary to avoid significantly underestimating runoff volumes when differences in CN values within a watershed are large or precipitation depth is small. The underestimation of runoff using the composite CN approach is a result of the nonlinear relationship between CN and runoff depth (Figure 2).

As the focus of stormwater management increasingly includes smaller storms, use of weighted vs distributed curve numbers becomes an even greater problem.  Peters comments that although composite curve numbers can continue to be a reasonable approach for very large storm flooding analyses, “…a composite CN approach for site specific stormwater management design within a proposed development won’t be appropriate for most communities.” distributed curve numbers are vastly preferable and more accurate.  The article includes a variety of additional practical recommendations, designed to improve modeling applications.

You can access the complete article here.

Our next post will look at A Better Way of Measuring BMP Effectiveness…

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Reminder: 2010 Schuylkill Watershed Congress this Saturday. We’ll be There Talking LID, Conservation Design

March 11th, 2010

2010 Schuylkill Watershed Congress
March 13th, 2010
Montgomery County Community College - West Campus
Pottstown, Pennsylvania

The Schuylkill Watershed Congress is an annual gathering of citizens interested in understanding, protecting and restoring local watersheds and streams. This event features a diverse program with concurrent and poster sessions covering a broad range of watershed topics.

The 2010 Keynote Presentation offers a panel discussion titled “How to Challenge a Stormwater Permit and Win: A Look at the Crum Creek Neighbors Decision. Michele Adams (Meliora Environmental Design), James A. Schmid, Ph. D. (Schmid & Company, Inc., Consulting Ecologists), and John Wilmer (Environmental Attorney), will tell the story behind the recent successful legal challenge to a stormwater permit given to a developer in an Exceptional Value designated watershed in Delaware County.

Complete details on all sessions being offered and for registration and sponsorship information can be found here

Registration forms can be downloaded here

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Philadelphia’s Stormwater Management Success Getting National Attention

February 23rd, 2010

As we noted in this post, Green Infrastructure is coming of age, and Philadelphia is at the forefront of utilizing innovative “greening” techniques. Be on the lookout for much more about these exciting efforts here on StormwaterPA in the coming months, including a series of videos that look at specific projects and sites.

In the meantime, amongst the useful articles in the January/February issue of Stormwater is one of special interest to us: “Philadelphia: Going Green to Manage Stormwater” (Margaret Buranen).  This is a nice acknowledgement of the Philadelphia Water Department’s nationally prominent green infrastructure program to better manage stormwater and the extremely serious combined sewer Overflow (CSO) problem.

Philadelphia’s changes in stormwater strategy began a major shift in 1999, when the City’s Water Department formed an Office of Watersheds to integrate sustainable wet weather solutions.

Dr. Christopher Crockett, PE, Director of Planning and Research at the Office of Watersheds:

In 2006, another major step forward occurred when we updated our stormwater regulations to require the management of the first inch of stormwater runoff for all directly connected impervious areas for any new or redevelopment with 15,000 square feet or greater of earth disturbance in the city.

The new regulations mean that “stormwater management” is part of the zoning and building permit process at the earliest stages.  Developers have many incentives to include LID and other green techniques to manage stormwater in order to meet those (2006) regulations.

Two years ago, the City Water Department proposed making a major change in the way billing was performed at the Water Department, essentially moving in the direction of a stormwater utility where stormwater billings for all non-individual residences would be based on impervious cover (80 percent weighting) and total lot size (20 percent weighting), rather than simply using water metering as in the past (notoriously inaccurate - large water users can generate relatively modest stormwater and large stormwater generators can use sometimes virtually no water!).  The new program has done much to encourage developers to incorporate partial and full green LID elements in new project designs.  Water Department success has been significantly reinforced with partnerships, such as with the Pennsylvania Horticultural Society’s Philadelphia Green.

In 2005, Philadelphia Green and the PWD started work on a project to address stormwater problems at seven Philadelphia schools.  At S. Weir Mitchell Elementary School, children created a raised bed vegetable garden in a paved parking lot, which will not only absorb stormwater, but also reduce the heat island effect.  Vegetation, infiltration trenches, bioswales,and a rain garden replaced some of the school’s 3-acre impervious site.

Another joint stormwater project, in South Philly, will include the city’s first sidewalk infiltration planters, on South 13th Street.  Modeled after street planters used in Portland, OR, they are designed to reduce overflows that led to basement flooding, a persistent problem in the area.  These planters, which measure 30 feet long by 7 feet wide and are 4 feet deep, will be filled with native plants suggested by members of the PHS.

Ms. Buranen’s Stormwater article includes a wealth of information on Philadelphia projects, and we urge you to take a look!  This is definitely a Pennsylvania stormwater success story! You can find the complete article here.

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Can Greening a City Reduce Stormwater AND Improve Quality of Life?

February 5th, 2010

There has been alot of talk about “green infrastructure” over the past couple of years–and communities all across the nation are slowly bmoving towards this more natural approach.

From USEPA:

Green infrastructure is an approach to wet weather management that is cost-effective, sustainable, and environmentally friendly. Green Infrastructure management approaches and technologies infiltrate, evapotranspire, capture and reuse stormwater to maintain or restore natural hydrologies.

At the largest scale, the preservation and restoration of natural landscape features (such as forests, floodplains and wetlands) are critical components of green stormwater infrastructure. By protecting these ecologically sensitive areas, communities can improve water quality while providing wildlife habitat and opportunities for outdoor recreation.

On a smaller scale, green infrastructure practices include rain gardens, porous pavements, green roofs, infiltration planters, trees and tree boxes, and rainwater harvesting for non-potable uses such as toilet flushing and landscape irrigation.

In Pennsylvania, these ideas are starting to take hold–and the Philadelphia Water Department is at the forefront of using green solutions to meet the challenges presented by rain. The Philadelphia Art Museum’s new Parking lot features a green roof and other landscape features to control runoff,  and the Water Department has started phasing in a new parcel based fee structure that encourages landowners to manage runoff on their properties rather than shunt it to the nearest sewers. The Inquirer looks at the city’s plan in an article published today.

EPA’s Managing Wet Weather with Green Infrastructure website is a great resource to learn more.

So are we: Stormwater PA is in the process of developing a series of video case studies that look at green infrastructure, so keep checking back; they’ll be available soon!

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