Even the little guys need attention too...

Some pics from the field, checking out minor bridges, culverts and tunnels in Denver this week.  Mr. Hitchman, resident Aussie, is an avid snake breeder/buyer/seller/protector and knows what he's doing... and this bull snake is non-poisonous.  Needless to say, I let the Aussie James go first.

Following up on the digital oranges...

A previous blog entry discussed the use of a cast-and-retrieve watertight GPS unit to track streamflow data through a bridge opening, and mentioned a comparison of modeling results to come.  The applicable project involved 1D hydraulic modeling of the tidal estuary and bridge using HECRAS.  Without going into the limitations of this modeling approach too much (compared to 2D), here is a short summary the effort.  The peak velocities for each track were extracted and reduced by 20% to convert from surface data to an approximate depth-averaged velocity.  Peak velocity predictions from the applicable tide cycle in the model were extracted for comparison per location along the crossing.  In most cases, the GPS recorded up to 2-3 times faster peak velocities than the model predicted.  This bust is primarily due to two issues with the 1D approach:  the model is not capturing the convergent (2D aspects) flow characteristics through the crossing (significant at this site), and the streamtube approach of the model is smoothing/averaging the data, removing the peaks.  A 2D model such as RMA2 would better capture those localized peaks around the substructure, as well as angles of attack.  Pulling the tracks into google earth and doing a simple averaging of the velocities between start and finish points confirmed the logging was good and gave velocities much closer to the model predictions.  Luckily, model calibtration was accomplished via on-site tide gage data.  In short, I look forward to using this field method on a future 2D estuary flow project and comparing ... oranges to oranges... exuce me - had to say it.

"north country hydrosurvey"... this is how we do it up hyinder in the woods..

"north country hydrosurvey"... this is how we do it up hyinder in the woods..

Holdin onto the dream!

http://www.youtube.com/watch?v=T-aZTi8bY3Q

Record flooding of Lake Champlain

Pics of flooded ferry dock back home. Lake Champlain is way above the past record stage set in the 1800's. Vermont filing for federal disaster assistance for first time since early 1990's.

Scuba inspection hints and gadgetry

I just came off of some underwater bridge inspections in Florida using the SCUBA approach.  I don't go scoobie-doo for work very often, but it works well for the small bridge spans and slow-moving clear waters of the Florida intercoastal and canals.  Thanks go out to the Florida dive crew that brought me up to speed on safe practices down there.  Besides the established safety guidelines and recommendations out there (see OSHA, ADCI and USACE) regarding manning and communications, here are some helpful tips and gadgetry to make this inspection method go more smoothly and safely. 

1.  Underwater slate - works very well for short term note-taking between surfacing to relay to topside crew.  It's a good idea to take photos of the notes prior to erasing, in case later reference is needed.

2.  Pony bottle (20 cu. ft.) with dedicated regulators for back up emergency air supply - this is now part of OSHA dive regs and seems to be becoming common place among recreational divers as well.  The 2nd stage for this bottle can be bungeed around the neck like cave-divers do, or just clipped on the BC close to your face like I did.  Of course, with the octopus I had 3 mouthpieces clipped close to my face, so make sure you know which one you're breathing off of!

3.  Helmet - I started donning my climbing helmet after a few bridges just to provide a mount for my video camera (see next item), but quickly grew attached to having it on.  Being a hardhat diver, the climbing helmet gave me a safe and reassuring feeling to have something on my skull besides a swim cap.  I thought it would be unfortable underwater, but in fact I hardly even noticed it was there and inadvertantly banged it off piles frequently.  It's not an industry requirement to wear head protection when on SCUBA, but I think I'm going to incorporate it into my normal gear.  A colleague in another company lost a good friend who was inspecting an outfall pipe on SCUBA in a pond with zero viz.  He dropped the camera on ascent, and upon descent to retrieve it, hit his head hard on the pipe end, lost consciousness, spit out the regulator and drowned.

4.  GoPro Helmet Camera - this was a birthday present a few year back to capture fun footage of mountain rides on my motobike.  I've never used it for that, but it's come in handy for work above and below water.  It attaches easily to my climbing helmet, and you can't even feel it's there underwater.  The housing is waterproof to 100 ft, and the camera is wide angle HD, capable of stills and video with audio.  Downsides are that it has no zoom function, needs relatively clear water and lots of light, and there is no instant playback.  It has a habit of shutting off prematurely if the batteries aren't absolutely fresh and new as well, which can be frustrating when you don't have time to stop and check it constantly.  I wouldn't use it as my primary underwater video if it's a required deliverable for the job, but it's good for a record - it holds about an hour of video at a time.  I use it alot above water without the housing as a sort of visual voice recorder for important items during inspections, and the footage for climbing inspections is awesome.  Short sample underwater video clip is found at http://www.youtube.com/watch?v=kdk7sQZm-rs

Google 'GoPro Helmet Camera' to find out more.

Be Safe out there!

Car-armoring?

A river geomorphologist I work with, Bill Spitz, sent this around - pretty crazy - the Japan tsunami has stacked these cars up in the same fashion as cobbles in river bed armoring...

Experimenting with animated slideshows for work - Death to PowerPoint!!!

http://tripwow.tripadvisor.com/tripwow/ta-010e-ec6a-28a1?ln

Tossing digital oranges into the river..

I've just returned from a site visit to a coastal bridge in New Jersey, making observations and collecting data necessary for tidal modeling efforts.  With a budget too tight for extended tide data collection using our usual suite of bubbler pots and acoustic doppler velocimeters, I was faced with the prospect of using the age-old technique of tossing oranges in the water to assess streamflow.  I don't mind going old-school to get the job done, but with an absence of NOAA tide data in the vicinity, I really didn't want to calibrate my highly advanced models with floating fruit, no matter how sustainable and earth-friendly the approach may be.  I needed an equally advanced but inexpensive and quick method to gage stream velocity and angles of attack.  What I came up with was basically a reusable, electronic orange - a sort of digital streamflow tracer.  Here's how it worked:  Borrowing an outrigger real from the survey locker and mounting it onto a Home Depot purchased aluminum rod, I created a rugged casting reel.  Also borrowed from the survey guys was a water-resistant Garmin Rhino GPS/walk-talk handheld unit, which I placed in a waterproof low-profile plastic pouch with external anchor point, purchased from West Marine.  Visiting the bridge at a full moon spring tide cycle, I repeatedly cast the unit into the oncoming tidal stream and allowed it to float freely under the bridge and around the piers before retrieving.  The Garmin unit was set to provide track data at 1 second intervals, including lat/long position, distance traveled per leg, velocity, heading, elevation and time/date.  Using mapping software on my field laptop, I was able to periodically download and check the data visually as it was acquired.  Post-processing of the data shows very few data fall-outs as the unit passed beneath the bridge, with very clean-looking lines of track data obtained after a little trimming of the toss and retrieve periods.  Samples of the streamflow tracers are attached.  Surface velocities will later be converted to depth-averaged velocities using open-channel flow principles, and used in model calibration at periods of peak flood and ebb tides.  Angles of attack will be used in pier scour predictions.  I will post more later on the results of this effort.  Some additional notes if you try this technique:  Don't bother with ziplock bags - they leak no matter how many times you double and triple bag and tape them up!  Get a real ocean casting rod and reel with 20 lb filament test if you can.  My homemade unit did not cast well - I ended up letting out a couple of bridge widths worth of slack and tossing the unit by hand.  Squeeze as much air as you can out of the pouch while still allowing floatation - you don't want the wind catching it at all during the drift.  The low-profile West Marine pouch shown lay flat on the water and worked very well.  Lastly, have a witty retort memorized and ready for use when the local fisherman ask "what the heck are you fishing for??"

Happy casting!

Marina Design: Fixed vs. Floating Dock Systems

Recent article written for Marina Dockage magazine discussing the pros and cons of various dock system types used in marinas and small craft harbor settings.  Enjoy, SZ