“Volume Based Hydrology” - A Much-Delayed Comment From the Editors

In the September issue of the Stormwater Journal, Andy Reese gives us an intelligent summary of stormwater management’s recent (and ongoing) paradigm shift - from peak rate control with detention basin solutions to control of total volumes of stormwater being discharged, using infiltration or evapotranspiration or capture and re-use and other management practice strategies including preventive Low Impact Development BMPs.

If you haven’t read the article, take the time and read it.  It’s enlightening and even entertaining (”As Mark Twain said, sacred cows make the best hamburger.”)  It’s gotten a lot of attention in recent months.  In “Volume-Based Hydrology” (or VBH, as he coins), Reese makes some provocative assertions (and know that we are barely even addressing the tip of the iceberg in our very summary comment here):

So it seems VBH is a water scarcity phenomenon

So, maybe VBH is a runoff volume reduction phenomenon.

VBH is really a stormwater pollution reduction phenomenon.

So it seems VBH is a channel erosion and habitat protection phenomenon.

So, VBH is a flood control phenomenon.

So…VBH is a floodplain management phenomenon.

Although we’re not sure that the technical arguments are as equally compelling for all of these stormwater management functions or benefits which Reese points out here (some do seem more important than others although relative importance may indeed vary with the specific situation, locality, watershed context, etc.), the point is that volume control is now known to provide much more bang for the management buck than previous strategies focusing exclusively on peak rate control.

This is a paradigm shift based on something of a revolution in our understanding of the stormwater problem itself and superior ways to prevent and mitigate these stormwater-linked problems.

It is important here to point out that the Pennsylvania Stormwater BMP Manual is substantially compatible with Reese’s VBH line of argument (he acknowledges this in the article).  The Manual’s Chapter 3, Recommended Stormwater Management Standards for Pennsylvania, sets forth an array of integrated peak-volume-quality standards which emerged as the Manual was being developed by PADEP, its consultant, and the Oversight Committee.  Assisted by the Villanova Urban Stormwater Partnership (VUSP) during the extended and arduous Manual development process, this set “recommended site control standards” emerged in many ways from thinking very similar to Reese’s VBH article discussion.  Reese develops a nice graphic showing it all as a kind of integrated set of objectives which work together to provide maximum management benefit:

Various stormwater objectives

This concept of integration is especially useful for so many developing Pennsylvania communities where this sudden paradigm shift in stormwater management, reinforced by state and federal mandates, is potentially too complicated and too costly and too politically challenging to embrace.  Yes, the bad news is that stormwater management is so much more complicated than we have conventionally understood it to be.

The good news is that this new “volume” focus which is designed to match pre-development and post-development hydrology allows us to accomplish so many stormwater management objectives in an integrated fashion and perhaps even reasonably cost-effective.

Use volume-based BMP strategies and related BMPs, and you can often go far in achieving volume and even peak rate (peak control for large storms is most challenging) and water quality and streambank erosion and flooding and floodplain objectives!  Many BMPs, (including many described in the PA Manual), give convincing performance across multiple objectives - clever design doesn’t require separate BMPs to satisfy management objectives.  With any degree of luck, you can kill two birds - perhaps even several birds - with one BMP stone.  Understanding the problem more completely is the first step in formulating a more comprehensive (and perhaps less complex and costly) solution.

Read the article.  Though some of this line of argument might vary a bit in other regions of the country with substantially different climate and physiography, we would argue that VBH and the discussion in the article is very applicable for so much of humid Pennsylvania.  Reese’s examples and interesting tables and graphs make sense in most of Pennsylvania.

Our only point of criticism is that this VBH paradigm shift article doesn’t in any direct way acknowledge the concept of prevention and its importance in this new management paradigm.  Preventive BMPs are given substantial attention in the Pennsylvania Manual.

The first step in comprehensive stormwater management - even before all of the vital objectives of VBH are wrestled with - needs to be ways to prevent runoff from occurring in the first place even as the same number of houses and square footage and cars are accommodated.

The complete article from the Stormwater Journal is available here.

Stormwater BMPs BMPs, capture and re-use, channel erosion, floodplain management, habitat protection, infiltration, LID, PA BMP Manual, peak rate, runoff prevention, stormwater best management practices, volume control