Archives 2016-01-05T23:55:50+00:00

Watershed Science Bulletin is a peer-reviewed journal that features articles about practical, science-based solutions to watershed and stormwater management issues.  Full articles are available only to members of the Center for Watershed Protection Association (CWPA) and Online Watershed Library (OWL) subscribers.


2010 through 2014 issues are now available for all to read. 2015 issues are available only to CWPA members and OWL subscribers.

Prior to 2013, the Bulletin was published in print 2xs per year. Articles are now published exclusively online 6xs per year to provide high quality editorial content more frequently.


July 2015

Introduction to the Clean Water Optimization Tool: Calculate Pollutant Removal Capabilities and Costs of Stormwater Best Management Practices

Hye Yeong Kwona*, Reid Christiansonb, PE, PhD, and Karen Cappiellac

a Executive Director, Center for Watershed Protection, Inc., Ellicott City, MD

b Water Resources Engineer, Center for Watershed Protection, Inc., Ellicott City, MD

c Program Director, Research, Center for Watershed Protection, Inc. Ellicott City, MD

*Corresponding author


The Center for Watershed Protection, Inc. developed a cost-optimization tool for stormwater management practices associated with reducing nitrogen, phosphorus, and sediment in the Chesapeake Bay. This planning-level tool will help communities struggling with identification and selection of cost-effective best management practices and provide them with initial guidance, as well as side-by-side comparisons for cost per unit of pollutant reduction strategies. Inputs are largely user customizable and results are geographically tailored. Several case studies are summarized and show the potential for substantial cost savings on pollutant reduction (sometimes more than 50%) when the most cost-effective practices are implemented to the maximum extent practical.




May 2015

Crosswalking between Gray and Green Infrastructure – Considerations for Budget Officers

Stacey Isaac Berahzer

Senior Project Director, Environmental Finance Center at the University of North Carolina Chapel Hill, NC,


As the green infrastructure (GI) approach to water management gains momentum, the local government budget process needs to adapt to some of the characteristics that make GI distinct from the more traditional gray infrastructure approach. As communities launch GI projects, shortcomings in the budgeting process can falsely create a bad first impression. When an inaugural GI project is grossly over-budget for installation or needs more frequent maintenance than planned, future GI projects may be blocked before the current project’s vegetation can become established enough to produce the significant benefits for which it was designed.

At the same time, the local government budget officer has not been the target audience for the tools and resources being developed in the GI field. This publication aims to provide a budget officer, or watershed proponent who seeks to influence a budget officer, some considerations in planning for certain key attributes of GI in the budget process.

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January 2015

A New Perspective on Opportunities for Stormwater Mitigation through Soil Management in Ordinary Urban Landscapes

Susan D. Daya* and David K. Mitchellb

a Associate Professor, Virginia Tech, Blacksburg, VA (

b Graduate Research Assistant**, Virginia Tech, Blacksburg, VA

*Corresponding author

**Current position, Owner, Mitchell’s Tree Care & Landscape Consulting, LLC


Renewed interest in green infrastructure as a stormwater management tool has focused attention on the effects of diverse landscape elements such as urban tree canopy, bioretention facilities, and rain gardens. However, ordinary urban landscapes—such as street medians, grounds of commercial and residential properties, and school grounds—make up much of the nonimpervious surface in urban watersheds and can be managed to increase their ability to receive and store rainfall. We propose that exploiting this potential creates an opportunity for a more holistic strategy for stormwater management where every portion of the landscape performs optimally, rather than solely relying on small, hyper-functioning cells. On average, urban soils are characterized by compacted soil, slow infiltration, and low hydraulic conductivity. Consequently, all such open soil areas are typically assumed to have lower stormwater management potential than their less disturbed rural counterparts. Soil preparation, root distribution, and selection and maintenance of surface treatments such as mulch, however, can strongly affect these characteristics, enhancing the ability of some urban landscapes to capture rainfall. We describe the potential of certain soil and vegetation management strategies to alter this “typical” behavior of urban landscapes. Although some of these practices are acknowledged as best management strategies, many are not or are infrequently implemented. Broader creation and adoption of such Best Management Practices (BMPs) combined with additional research has potential to encourage more optimal management of ordinary urban landscapes to improve water quality.

It is common knowledge that urbanization results in greatly increased impervious cover, but it also strongly affects the characteristics of the remaining soils—and both of these alterations in land surface cover contribute to increased stormwater runoff generation. During typical land development, vegetation is removed, soils are compacted, and some areas are covered by impervious materials. The few soils that are not covered after development are generally highly disturbed, and they become saturated quickly and do not drain well. Thus, in addition to there being more impervious surface, the amount of precipitation captured and stored in the remaining soil and vegetation decreases and runoff increases. In spite of there being considerable interest in parcel-level stormwater management approaches in urban areas (e.g., low impact development) that rely on rain gardens, bioswales, and a variety of other engineered, plant-based installations, little attention has been directed to attenuating stormwater through increasing the ability of landscape soils and vegetation outside of such hyper-functioning systems to support stormwater-related ecosystem services on a wider scale in urban land. We suggest that it is time for more attention to be paid to the soils and plants resident in the myriad unpaved soil surfaces present in the built environment—the ordinary urban landscape—and their potential for mitigating stormwater runoff in urbanized watersheds.

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November 2014

Potential Application of Stormwater Banking in the Chesapeake Bay Watershed Using Two Case Studies

Cappiella, Karena*, Bill Stacka, Joe Battiataa, Dan Neesb, and Lisa Fraley-McNealc

a Center for Watershed Protection, Inc., Ellicott City, MD,

b Environmental Finance Center at the University of Maryland, College Park, MD

c Anne Arundel County Watershed Protection and Restoration Program, Annapolis, MD

*Corresponding author


Managing stormwater in urban environments involves numerous implementation constraints that make full on-site compliance with stormwater management regulations difficult and/or costly. In the Chesapeake Bay watershed, demand for innovative strategies that reduce the costs of stormwater compliance is driven by the need to comply with state stormwater regulations and MS4 permits (which contain provisions for meeting the Chesapeake Bay TMDL) and by the desire for stormwater fee relief for large property owners.

Stormwater banking has the potential to reduce costs for stormwater permit holders and, when coupled with local incentives, can open up an inventory of properties that would not have otherwise been targeted for restoration while at the same time facilitating local water quality improvements across urban communities. This paper describes the potential application of stormwater banking to the stormwater compliance landscape in the Chesapeake Bay watershed, based on a case study analysis of supply and market drivers in Baltimore City, Maryland and the City of Hampton, Virginia. This study found a large supply of potential BMPs and credits in the City of Hampton; however, the supply is dwarfed by the number of sites necessary for the City to meet their TMDL requirements. In Baltimore, the supply of appropriate vacant sites is much greater than what is required for TMDL compliance; however, implementation of BMPs on these sites is only feasible if the banking program is able to successfully incentivize redevelopment. The next step for the case study communities is to evaluate the demand for stormwater banking through surveys that will also help to determine the appropriate price points for stormwater fee credits and local redevelopment incentives.

The potential for stormwater banking to offer compliance options that save money for the regulated MS4, developer, or stormwater fee ratepayer lies with the ability of the program to effectively prioritize projects with the following characteristics:

  • Low-value land
  • Large-scale projects
  • Performance-based contracting
  • Wide range of project types
  • Location within the jurisdiction

While the above local stormwater banking structure is designed to address the specific demands and regulatory environment of the Chesapeake Bay watershed, it almost certainly could apply in other parts of the country. Each of these scenarios can meet multiple goals of improving local water quality, stimulating the local economy and revitalizing communities by encouraging redevelopment and greening neighborhoods.

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June 2014

Building the Next Generation of Smart BMPs: Media Enhancements for Phosphorus Removal

Law, N. La*, R. D. Christiansona, L. Fraley-McNealb and G. Hoffmanna

a Center for Watershed Protection, Inc., Ellicott City, MD

b Watershed Protection and Restoration Program, Anne Arundel County Government, MD

*Corresponding author,


The science and practice of stormwater management to improve best management practices to protect and restore water resources is an ongoing field of study. Innovation to develop smart BMPs is an essential component of stormwater management given the high cost of retrofitting urban areas and required pollutant load reductions to meet TMDLs and other local program goals.  The focus of this paper is a review of the use of media additives to enhance the phosphorus (P) removal from BMPs and to identify information needs to move this innovation from research to practical application. A review of different types of additives and their pollutant removal capabilities is described along with information needs to move this smart BMP from research into practice.

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February 2014

Pollutant Analysis of HVAC Discharges in Montgomery County, Maryland

Lori A. Lillya*, Neely L. Lawb, Alexander Torellac, Daniel McCannc, and Pamela Parkerd

a Watershed Ecologist/Planner, Center for Watershed Protection, Ellicott City, MD,

b Senior Research Analyst, Center for Watershed Protection, Ellicott City, MD

c Environmental Compliance Inspector, Montgomery County Department of Environmental Protection, Rockville, MD

d Stormwater Permit Coordinator, Montgomery County Department of Environmental Protection, Rockville, MD

* Corresponding author.


In the Chesapeake Bay watershed, a Bay-wide total maximum daily load for nutrients and sediment is driving state and local efforts to account for every pound of pollutant that can be prevented from entering the Bay. Much of the effort focuses on the treatment of uncontrolled stormwater runoff; however, nonstormwater discharges have a significant and quantifiable pollutant load, much of which can be detected and eliminated through the effective implementation of an illicit discharge detection and elimination (IDDE) program. Montgomery County, Maryland, a Phase I municipal separate storm sewer system (MS4) operator, found an unexpected and ubiquitous source of pollution to the MS4 during routine IDDE investigations. The County initiated a special IDDE study on pollutant contributions from heating, ventilation, and air conditioning (HVAC) system discharges. Of the 73 buildings assessed, 27% had a potential HVAC discharge. The study found elevated concentrations of nitrogen and heavy metals, most of them exceeding water quality standards. The sources of contamination were biocide products, illicit cooling tower connections, water from condenser coil washdown, and refrigeration leaks. Given the ability to identify and quantify HVAC discharges, we provide management and research recommendations to eliminate this illicit discharge and improve methods to detect this source through IDDE programs.

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December 2013

Using Nutrient Credits and Offsets To Achieve Stormwater Compliance with the Chesapeake Bay TMDL: A Discussion Paper

Karen Cappiellaa*, David Hirschmanb, and Bill Stackc

a Program Director, Research, Center for Watershed Protection, Ellicott City, MD,

b Program Director, Center for Watershed Protection, Ellicott City, MD

c Deputy Director of Programs, Center for Watershed Protection, Ellicott City, MD

* Corresponding author


Nutrient credit trading in the Chesapeake Bay watershed offers both risks and opportunities for meeting total maximum daily load (TMDL) nutrient reduction targets. Although most of the Bay states and the District of Columbia have already established nutrient trading or offset programs, the vast majority of trades have involved wastewater treatment plants, with little involvement from the stormwater sector. The Bay jurisdictions are now more fully exploring the role of stormwater compliance credits in state nutrient trading programs.

This paper discusses the potential to generate and purchase nutrient offsets and/or credits as a compliance option in response to the Chesapeake Bay TMDL and state stormwater regulations. We present a summary of the requirements for stormwater permittees who must comply with state stormwater regulations and the challenges of compliance with the Chesapeake Bay TMDL. We discuss three scenarios to generate and purchase stormwater credits and offsets as part of a potential structure for achieving future compliance.

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October 2013

Ask the Experts: Stormwater Utility Development and Public Support

In addition to peer-reviewed research, the Bulletin features interviews with experts in the watershed and stormwater professions discussing a specific topic. Here, three professionals weigh in with their perspectives on establishing stormwater utilities to fund water quality restoration projects.

Stormwater utilities can provide a reliable source of funding for the operation of stormwater programs, maintenance of stormwater infrastructure, and compliance with stormwater permits. The funds are generated from fees charged to landowners for the amount of stormwater produced on their property; the fees are typically based on factors that influence stormwater runoff, such as the amount of impervious surface. While many communities across the country have established stormwater utilities, many more have not and may be unsure how to begin and how to justify it to gain public support. Our experts include representatives from jurisdictions that have established stormwater utilities and from an advocacy organization that has been heavily involved in gaining support for stormwater utilities.

Here is what our experts had to say…

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August 2013

A Private Incentive-Based Stormwater Mitigation Program To Enhance Stormwater Management Control beyond Current Minimum Standards in Residential Subdivisions

Matthew C. Hubera,* David B. Willisb, Charles V. Privette IIIc, and John C. Hayesd

a Graduate Teaching Assistant, The John E. Walker Department of Economics, Clemson University; Clemson, SC;

b Associate Professor, School of Agricultural, Forestry, and Environmental Sciences, Clemson University; Clemson, SC

c Associate Professor, School of Agricultural, Forest, and Environmental Sciences, Clemson University; Clemson, SC

d Professor Emeritus, School of Agricultural, Forestry, and Environmental Sciences, Clemson University; Clemson, SC

* Corresponding author


Incentive-based stormwater management policies offer the prospect of reducing urban stormwater runoff while increasing developer profits. This paper describes an incentive-compatible developer-based stormwater mitigation program (DSMP) that would enable both outcomes. Under a DSMP, developers would be able to earn additional profits by building at higher residential densities in exchange for including low-impact development stormwater best management practices in the development’s stormwater management infrastructure. One can modify the parameters of the DSMP to fit location conditions and multiple policy objectives.

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June 2013

Accounting for Future NPDES-Permitted Pollutant Loads in Waste Load Allocations for Municipal Stormwater

Michael D. Trojana and Anna M. Kerrb*

a Hydrologist, Minnesota Pollution Control Agency, St. Paul, MN

b Pollution Control Specialist, Minnesota Pollution Control Agency, St. Paul, MN,

* Corresponding author


In linking National Pollutant Discharge Elimination System Phase II municipal separate storm sewer system (MS4) permits to total maximum daily loads (TMDLs), proper derivation of the waste load allocation (WLA) is critical. A TMDL WLA sets a cap on pollutant loading and may restrict growth and development. To avoid having to reopen a TMDL, the WLA should include pollutant loads from the future urban footprint, as determined using land use or orderly annexation plans. The WLA should also include loads associated with discharges from MS4s that will be designated for permit coverage in the future. One can account for the discharges related to these MS4s using information on population trends and projections. Accounting for discharges resulting from urban growth or future permitted MS4s in the WLA reduces the likelihood that a TMDL will need to be reopened and provides permittees with flexibility in managing their stormwater discharges.

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