The Stormwater Blog 

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

Rainwater Harvesting and Make Up Water: The Why, When, and How

Rainwater harvesting (RWH) stores rainwater for reuse to supply non-potable uses like irrigation, wash water, toilet flushing, and laundry.  During long dry periods the demand will drain the storage cistern down to a critical level where the pressurization pump(s) will need to shut down to prevent dry run damage.  Make up water is typically a potable connection to the rainwater harvesting system to supply water, allowing the RWH system to continue to supply the non-potable end use applications until the next storm event refills the storage cistern.

Guidance for Ensuring Bioretention Media Performance Success Part 2: Specifications, QA/QC and Certification
As mentioned in Part One of this blog post series, a successful bioretention media installation must have a framework in place as guidance for managing media from inception to installation. The framework should not only include Standard Operating Procedures (SOPs) or how to source, qualify, verify, produce, store, and handle media, but also include media specifications to ensure recipe consistency.
Categories: Bioretention
Guidance for Ensuring Bioretention Media Performance Success Part 1: Standards of Practice
Engineered media is the heart of bioretention system performance. Therefore, preserving media integrity is of the utmost importance. A successful bioretention installation involves oversight not just onsite, but having a framework in place for transferring raw materials to a blended, commercially installed product. 
Categories: Bioretention
Filter Fabric in Detention and Infiltration Systems

It’s never surprising to see some type of fabric or geotextile called-out around an underground detention or infiltration system. The note is common across civil plans everywhere, but how is a geotextile selected as applicable for the particular underground system the detail was so aptly created? The answer to that question starts with one step back – why we even use filter fabric.

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?

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