The Stormwater Blog 

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


Infiltration


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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.

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.


Is Corrugated Metal Pipe Suitable for Subsurface Infiltration?
Some engineers are hesitant to use CMP (corrugated metal pipe) for stormwater applications because they have read or heard about CMP being used in culverts that have corroded. This shouldn’t be the case. Many decades ago, galvanized pipe was the coating of choice for culverts; that now has been replaced with Aluminized Type 2 (ALT2). 
Stormwater in the west: Use it or lose it!

At about 2.5% of the total water volume on the planet, we’ve always had roughly the same amount of freshwater. Unfortunately, it seems that, at the local level, the amount of fresh water made available through precipitation is increasingly erratic, with the last year featuring historic floods in the eastern US and historic drought in the west. In my adopted home state of California, 2013 was officially the driest year on record and snowpack, groundwater and reservoir levels throughout the state are critically low. Although we’ve undertaken extensive engineering feats in the form of reservoirs, diversions and water supply pipelines, local water management decisions provide our greatest leverage on local water supply.

Stormwater Infiltration Explained

Stormwater infiltration is defined as the process by which water enters the soil and recharges streams, lakes, rivers, and underground aquifers. Stormwater infiltration is a fundamental component of the water cycle and is quickly becoming the centerpiece of stormwater management strategies across the United States. Stormwater infiltration is an effective means of managing runoff because it allows practitioners to address both water quality and water quantity concerns.

Thinking Outside The Box: Infiltration System Layouts
Historically, underground infiltration beds have been laid out in either square or rectangular shapes, sometimes far away from where the actual rain drops fall. These large systems are typically fed by a series of upstream catch basins and conveyance pipes. Several factors contribute to site layout, but mostly it simplifies the hydrologic and hydraulic modeling process, and keeps infiltration beds away from more sensitive underground infrastructure.
Traditional stormwater criteria require both improving the quality and managing the quantity of runoff. One of the best practices is to incorporate pretreatment, detention and treatment into an integrated system. This approach can meet total daily maximum load requirements by providing a high level of pollutant removal and preventing erosion damage from peak flows. Many areas may require only some of these processes while some areas may require all of them.
Stormwater Infiltration: Drain-Down Characteristics of Hydrologic Soil Groups
Infiltration plays an increasingly important role in meeting stormwater runoff mitigation regulations. One of the primary considerations for infiltration feasibility is the runoff routing. Infiltration systems must drain in a reasonable amount of time to avoid creating mosquito habitat and to recover storage volume for subsequent storms.
Categories: Infiltration
Structural Considerations for Stormwater Control Measures
As the need for effective stormwater treatment and volume control grows, so does the number of available stormwater control measures (SCMs) such as filtration systems, hydrodynamic separators, bio-retention  systems, green roofs and pervious pavement. As part of their due diligence, engineers go through an evaluation process to determine if the proposed system will meet some basic criteria, one of which is structural considerations. Below are some of the structural considerations.  The engineer should not assume that because a SCM is approved and/or detailed in a manual that all of the structural issues have been addressed. 
Three Components of Infiltration System Design
Common infiltration practices include drywells, bioretention, permeable pavement, infiltration trenches, infiltration basins, and subsurface infiltration galleries. Regardless of their form, all infiltration systems have three primary components: storage, treatment, and infiltration.
Categories: Infiltration
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