Sheetflow

March 25, 2011

Check Dam Installation Example

Filed under: Photo, Video — Sheetflow @ 7:04 am

Check dams need to be installed so that the center point of the dam is at least 8 inches lower than the outside edges; 12 inches in areas where intense rainfall occurs. If the center point is higher than the outer edges, water will run around the dam and erode the side slopes of the ditch, causing erosion. See Video.

March 20, 2011

The More Grass the Cleaner the Water

Filed under: Video — Sheetflow @ 9:42 pm

The Clean Water Act requires construction sites to meet water quality standards. One of the standards is turbidity, the measure of the cloudiness of water. Turbidity is measured in NTUs, nephelometric turbidity units, using a turbidity meter. The turbidity meter shines light through a water sample and measures the light intensity difference between the light emitter and collector; the cloudier the water, the higher the NTUs. The chief cause of turbidity in construction stormwater runoff is fine soil particles; fine silts and smaller. Persistent turbidity is caused by colloidal soil, particles which are so small the soil particle’s negative electrical charge is stronger than the force of gravity. This causes the particles to remain in the water column for long periods of time. Particles of this size do not settle out. The best way to keep the colloidal particles from entering stormwater is to protect the soil surface, both from the force of raindrop impact, as well as the shear stress of flowing water. Vegetation is the single best way to protect bare soil from these forces; the more vegetative cover the better. In this video, the affect of grass cover is apparent. Turbidity samples, taken from runoff from a grassy area with 70 to 80 percent soil cover is under 25 NTUs, the allowable discharge number.

March 15, 2011

Revenge of La Nina

Filed under: Uncategorized — Sheetflow @ 8:48 pm

Putting aside the cross-Pacific radiation issues for this blog (again, absolutely no reason to be concerned here on the West Coast), we have had notable very heavy precipitation during the past several days. Slides have stopped north-south train traffic, strong thunderstorms with thunder and lightning have pummeled the lowlands, and some mudslides have blocked local roadways. Slides on the rail right of ways has become a major problem–take a look at the video on the side bar (to the right) to view a typical NW landslide on to the tracks between Seattle and Edmonds.

Lets start with the precipitation over the last two weeks at Sea-Tac (see graph): roughly twice normal–so half way through the month we have “enjoyed” a normal whole month’s total.

Here is the cumulative precipitation (top figure) this season for the Cedar/Tolt rivers (the main water supply of Seattle). Yes, we are ahead of normal (consistent with La Nina). The bottom panel shows snowpack for these watersheds–rapidly catching up to normal after being well below normal. You will be able to water your lawn this summer.

Looking at the precipitation for the last 48h from Seattle Rainwatch
An amazing 4 to 6 inches from north Seattle westward. No wonder there were slides on those tracks!

For days we have been getting very heavy bands of convective showers moving through. Take today at 2:30 PM (see below). Lots of yellows (heavy rain) and even some reds (downpour and or hail).
One very heavy thundershower moved through this afternoon and an image shown on the KOMO-TV website (reproduced below) strongly suggests a rotating “wall cloud”. I would not be surprised at all if someone saw a funnel coming out of this feature.

More rain tomorrow…but believe or not, Thursday and early Friday should be dry!

Returning briefly to the tsunami issue…it turns out that my idea of building safety towers has been considered for a long time (should have known)…it is called vertical evacuation. There are a few projects being considered on the Oregon and Washington coasts…but nothing sufficient to deal with the problem. What will it take to make the investment to build enough vertical evacuation facilities to have a hope of saving most of our coastal population in case of NW tsunami? This is also homeland security–for a fraction of the funding used to building that fence along the Mexican border we could protect all our coastal folks.

Catch Basin Open to the Rain

Filed under: Video — Sheetflow @ 7:00 am

When inspecting a project, I always look closely at the storm drain system to verify whether any dirty water from the project will drain to an active system. In this example, the catch basin has been installed but the main line it is connected to is not active.

March 10, 2011

Fugitive Dust Control for Truck Drivers

Filed under: Article — Sheetflow @ 3:01 am





















FUGITIVE DUST CONTROL for TRUCK DRIVERS

  • Wet loads with a fire hose.
  • Ensure adequate freeboard.
  • Cover loads.
  • Reduce speed on unpaved haul roads to less than 15 mph.
  • Stay on gravel haul roads.
  • Stay on paved haul roads.
  • Avoid driving through mud and wet soil.
  • Brush off mud from wheels, wheel wells, running boards and tail gates.
  • Wash wheels and inner fender wells immediately prior to exiting. Use a tire wash if available.
  • Call the truck boss for vacuum sweeper or water truck if you see trackout or visible dust.

FROM: Guide to Handling Fugitive Dust from Construction Projects, AGC of WA Ed. Foundation. 1997
MODIFIED for the WEB: David S. Jenkins, 2/2009

Heavy Rain

Filed under: Uncategorized — Sheetflow @ 12:04 am

Some amazing rain today…here is the radar image at 9:56 PM tonight…wow…lots of yellows–that is all heavy rain. It is pounding on my roof right now.


And today with the front there was a very intense rainfall band crossing the Sound around noon…here is the radar image. If you look closely, there were some reds in there….a downpour, probably with some small hail mixed in.

You might be interested in the quantity you are looking at in these images…they are reflectivity–a measure of the scattering of the microwave radiation emitted from the radar. The units are dbZ. You know about dbs on your sound system (db stands for decibel)..a logarithmic system for noting sound volume. This is a logarithmic scale for radar reflectivity.

5-10 greys-light mist or drizzle
15-25 light reds or pinks–light rain
30-35-moderate rain…greens
40-45 -heavy rain…yellows
Above 50–either absolute pouring or hail (reds)

Here is the rain over the past 24-hours from Seattle Rainwatch…some locations have gotten 1.5-2.5 inches today. Nice rainshadow.

March 5, 2011

Construction Project Designed to Keep Clean Water Out

Filed under: Video — Sheetflow @ 3:00 am

During project design, it is important to develop a storm water management basis for design. This is done primarily for the permanent storm water conveyance systems, but is is also important to do this for the temporary erosion controls which are, in effect, a temporary storm water conveyance system. This project, though covering a small area, drains directly to a creek which is tributary to an important salmon spawning river. In addition, there was some risk that the project might not be complete before the fall rains would begin. Because of these things, the basis of design process led to a system of clean water diversion and site water collection and dispersal into vegetation.

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March 1, 2011

Bonded Fiber Matrix BFM Uniform Coverage

Filed under: Video — Tags: , , , , , , , , , — Sheetflow @ 7:00 am

How to inspect bonded fiber matrix (BFM) application.

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