Friday, January 6, 2017

Why Is 48th Avenue NE Sidewalk On East Side Of Park Constantly Wet?

Several residents emailed the Laurelhurst Blog inquiring why the sidewalk on the east side of Laurelhurst Park on 48th Avenue NE is always wet and often has multiple puddles.

A neighbor said:

Thanks for looking into the sidewalk condition on 48th Ave NE for me. I know it is not legal to have dirt running off of properties so I hope the City can address it. Walking in the street has already resulted in people honking their horn at me.

Another neighbor said:

Has anyone else noticed how bad the sidewalk has become along the {ark at 48th Ave NE? It appears there is no drainage along the Park's steep bank so it is constantly covered in standing water, mud and dirt that runs onto the sidewalk and into the street. There are also a lot of tree branches.  
Unfortunately there isn't an alternative on that street because there is no sidewalk on the other side. Is there someone that manages this that could be called?

The Laurelhurst Blog contacted SDOT (Seattle Department of Transportation) who said that the inquiry was routed to Seattle Parks and Recreation Department (PKS), since PKS owns and manages Laurelhurst Park. 

A PKS Senior Civil Engineer for PKS was then sent to the site and reported:

A representative from PKS drainage and wastewater crew and myself have since visited the site and observed the groundwater flow over the sidewalk.  Generally speaking, groundwater flows are naturally occurring and directly tied to ever-changing geologic and hydrologic conditions that are difficult to predict.  Groundwater flows have been known to appear, disappear, and change flow patterns over time.  As a result it is often not practical to attempt to mitigate these conditions by installing static subsurface or drainage systems.
For the groundwater along the sidewalk on 47th Avenue NE specifically, it is likely from locally infiltrated storm water from Laurelhurst Park or subsurface spring conditions that may exist.   The northeast portion of the park has an underdrainage system for the ballfield. That subsurface drainage system is designed to keep the field surface from being overly wet during use, thus preventing rutting and other surface damage.  The remainder of the park is intended to infiltrate rainwater into the subsurface mimicking natural conditions as much as possible.  The majority of the soils are sandy, allowing water to percolate into the ground, however, there is a dense layer of silty soils that conveys water laterally.  It is likely due to this natural condition that groundwater seepage is noted along the sidewalk.

Capturing groundwater and conveying it to a drainage system is typically not allowed in the City of Seattle.  Groundwater flows can occur year around and would constitute a base flow in drainage or sanitary sewer systems.  Base flow takes away capacity needed to accommodate high volume or long duration rain events.  This could result in possible backups, combined sewer overflows, and/or sanitary sewer overflows.
Unfortunately, because of these reasons, neither PKS nor SDOT have a program to install infrastructure to address groundwater issues, but rather try to manage the impacts via direct surface maintenance when problems arise.   
If you note that conditions along the sidewalk are dangerous due to ice during the winter months or slick with algae during the summer months, please do not hesitate to contact our 24-hour maintenance line at (206) 684-7250.  If this is a condition that exists in the right of way or on the roadway surface, please contact SDOT during business hours at (206) 684-7623 or after hours at (206) 386-1218.

In summary, the seepage in question does not constitute a condition that PKS or SDOT will address with any infrastructure installation, modification, or improvement. 


Anonymous said...

The goal is to keep as much surface water out of the sewer system! During heavy, prolonged rain storms, the surface drainage overwhelms the system and results in overflows and backups.

Anonymous said...

I grew up in the neighborhood. The sidewalks on 48th Ave NE beside the playfield have always been wet during the winter.