The Stormwater Blog 

Contech Stormwater experts discussing Low Impact Development, Onsite Water Management, Rainwater Harvesting and all things Stormwater.

Bioretention Part Three: Lessons Being  Learned – Siting Issues and Inlet Design

Not done with siting issues yet, maybe this becomes five parts? One issue on siting and design is the hydraulic grade lines. Recall from your road drainage days the equations that were used to space catch pits and throat openings? The equations allowed for you to estimate gutter efficiency and top width for specified design storms. Well, these equations still apply, and I am thinking maybe even more considerations for very low flows.

Bioretention Part Two: Lessons Being Learned - Design Considerations

As a volume based stormwater control measure, bioretention systems are providing beneficial use in that they reduce runoff volumes and peak flows. In areas where combined sewers are an issue bioretention can reduce CSO frequency while increasing evapotranspiration and helping with groundwater recharge via infiltration processes. Common design criteria include storage volume and a design infiltration rate of the media and the underlying native soils. These criteria are tied to the site characteristics and statistical hydrology, for example, design the storage volume such that 95% of the mean annual runoff volume is retained. In addition to these sizing criteria we also need to design with these other factors in mind.

Bioretention Part One: Lessons Being Learned

As bioretention becomes more popular, many types of designs are being deployed throughout the U.S.  Though relatively simple in concept, many are finding that the devil is in the details with respect to maintenance and performance.  These issues are driving newer designs and improving criteria for use. Over my next few posts, I will be sharing some of the experiences and lessons learned with bioretention design. 


Top 11 Acronyms Every Stormwater Engineer Should Know

We are an industry of abbreviations and acronyms. The terms we use on a daily basis can sometimes hold a general or broad meaning in our minds, but the actual definition of these terms may leave our thumbs hovering over the game-show buzzer. To help ease the furrowed brows, we have collected and defined the top 11 terms every Stormwater Engineer should know:

Categories: Regulations
EPA Guidance Provides New Options for Meeting TMDL Goals

The goal of the TMDL program is arguably simple - to develop watershed level conservation plans designed to restore impaired waters and attain applicable water quality standards – but its development and implementation has not been simple. In an attempt to bring new clarity to the process of incorporating TMDLs into stormwater permits, the EPA issued a revised guidance document last November entitled “Establishing Total Maximum Daily Load (TMDL) Wasteload Allocations (WLAs) for Storm Water Sources and NPDES Permit Requirements Based on Those WLAs”.

Hydrodynamic Separators vs. Oil/Water Separators

There are a vast number of stormwater separators on the market which can make it challenging when selecting the ideal solution for each project.  Hydrodynamic separators and oil/water separators are often used interchangeably in the industry but each system is unique and one may be better suited for the overall treatment goals of the project.   So what is the difference between a hydrodynamic separator and an oil water separator and how can you determine which one is best suited for your project?

Media Filtration vs. Membrane Filtration: What’s the Big Difference?

Stormwater regulations are increasing calling for an increased level of treatment. This often takes the form of filtration systems. Two types of filtration systems used in stormwater are media filtration and membrane filtration.

Media Filtration systems are defined as filters that function through the use of physical capturing of pollutants, as well as absorption of pollutants through chemical reactions.  Typical media based filtration systems are composed of sand, stone, organics, or other materials.  The media utilized is typically chosen to target specific pollutants for removal.

Categories: Treatment, Filtration
Rainwater Harvesting Filters Explained
Most people do not think about how they get the water they use; they just turn on the tap and the water is there. The same holds true for rainwater harvesting (RWH) systems. Most people understand there is a cistern that collects and holds the harvested water. But what they may not realize is that with every large scale RWH system there is a mechanical system that pumps, filters, and treats the harvested water before it can be reused.
Subsurface Infiltration as a LID Stormwater Management Strategy
The only sure way to eliminate stormwater pollution is to eliminate stormwater runoff. In recognition of this fact, Green Infrastructure (GI) and Low Impact Development (LID) practices have prioritized runoff reduction as a primary regulation for stormwater management.  These practices have proliferated throughout the United States.

Rainwater Harvesting Disinfection Methods: Treat It Before You Use It
Using harvested rainwater is not new, it has been in practice for thousands of years (3000 B.C., and may be even earlier).  But we have something that wasn’t available back then; the ability to disinfect rainwater to make it safe for human contact or ingestion.  Harvested rainwater can be safely used outdoors and indoors if the correct steps are taken to treat it. The type of disinfection depends on how the water is going to be used and the requirements of local plumbing codes.  With modern disinfection, rainwater can even be filtered and disinfected to potable standards.
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