Showing posts with label Storm Flow. Show all posts
Showing posts with label Storm Flow. Show all posts

Friday, April 10, 2015

Rain and Flooding

Blue Jay Barrens is about as wet as it can get.  A long sequence of storms moving through during the past week has dropped nearly six inches of rain over the area.  Storm clouds moved through once or twice every day.

The soil, already fully hydrated by over six inches of rain in March, quickly became saturated and the output of each storm had nowhere to go but to run overland to the creek.  A storm yesterday afternoon produced 0.8 inches of rain in 15 minutes.  The result was a flash flood, the third this week.

Water from the township road carried red clay particles to the pond.  It looks like a bowl full of mud, but the water clarity is not as bad as it appears.

A closer examination shows the water to still be fairly clear.  The clay tint makes the dark Wood Frog tadpoles easy to see. 

The tadpoles have just recently taken on the traditional tadpole shape and become free swimming.  If these rains persist, there will be no problem of the pond drying up before the tadpoles transform into little hoppers.

The diversions around the vegetable garden have been working overtime this spring.  The garden sits in a level area that was formed by eroded soil being trapped by an elevated roadway.  Without the diversions, water would inundate the garden after every rain.

After each storm, I check to see that the female Carolina Wolf Spider is alive and well.  So far, she seems to have been unaffected by even the heaviest of rains.

Small upland waterways swell to wide streams as the water quickly rushes downhill.  After each rain event, I try to get down to the creek to see how the increased water flow moves through the channel.

The quickest way to the creek is over the hill.  Even in the driest, most well drained locations, water still stands on the surface.

Five minutes after the rain has stopped, concentrated water flow is still pouring from small woodland watersheds along the creek. 

Water running from these woodland areas is generally clear, but it carries a heavy load of leaves.  The result is a mosaic of bare ground and thick piles of leaves.  This will influence the pattern of plant growth through the rest of the year.

I’m always relieved when I see the bridges still intact.  All but one of the bridges have been replaced to an elevation above the record flood level.  If we do get a flood capable of tearing out this bridge, I hope I’m here to see it, because it will be a truly rare and terrifying event.

Calm and scenic features, such as a small waterfall, are covered over by the flood.  It’s always a surprise when the water drops and the creek resumes its earlier appearance. 

Water pools in the flood plains as it waits for a chance to seep into the ground.  This soil is very well drained and normally allows rapid water infiltration.  Its appearance now makes you think of vernal pools and amphibian breeding, but given a day without more rain, it will pass all of this water into the creek.

This is the last bridge needing to be repaired and elevated.  It has been moved and battered by flood water many times over the years.

Downstream of the bridge is the area blocked by a log jam a couple of years ago.  Since the removal of the jam, water now flows freely through the channel.

Since I wait for the lightning to clear the area before venturing out after a storm, I usually miss seeing the water at its highest level.  At the peak of the flood, water left the creek channel and moved overland.  This area was scoured clean when the water was suddenly blocked by the formation of a log jam and forced out here.  It’s likely that a new channel will be formed here someday.  I could have left the log jam in place and let the new channel form, but this little area has a nice collection of woodland flowers that I would like to enjoy for a while longer.

The third of three large bridges is now well above flood level.  This bridge was repaired using sections of decking from two older bridges.  I think this one is elevated and anchored well enough to withstand any flood.

I find still photos of rapidly moving water to be lacking in impact, so I have included a short video that captures the movement and sound of the angry creek.  It is also available for viewing on YouTube by clicking HERE.

Sunday, March 14, 2010

Storm Flow

Storm runoff yesterday offered some good examples of how increased water flow changes the stream course. Water above the dam is temporarily slowed by the obstruction. Water velocity increases as it is forced through a narrower opening and increases again as it rapidly falls to a lower elevation. Turbulence combines with the increased speed and the water is able to change the shape of the downstream channel.

The turbulence from the fall travels as waves of energy down the stream bed. Water striking the streambed is deflected upward where is can again fall. These energy pulses effectively knock pieces of loose materiel up into the water column where they can be washed away.

The water’s energy is directed to the bank on the outside of the curve. The bank suffers a little bit of erosion each time this happens. This increase in flow was produced by 1.25 inches of rain in a 12 hour period. Streams are subjected to this type of flow several times each year and are subtly shaped by the action of the water. Out of bank flood events are a much rarer occurrence and have a different effect on the stream.

Obstructions, such as the fallen tree, add to the complexity of the flow pattern. This obstruction is causing the water to accelerate through the narrow opening to the right and is causing an outward bow to the stream bank.

Two tributaries join in the center of Blue Jay Barrens. Both of these tributaries begin on neighboring properties and the water quality is a reflection of the activities taking place on those properties. The stream on the left always exhibits a higher degree of turbidity.

The amount of sediment attributed to stream bank erosion is minimal. The sediment shown here is a result of poor upland soil condition and cover. There are a few small watersheds that are entirely contained within Blue Jay Barrens. The clear water entering from the right is from one of these watersheds. Proper land management could allow these streams to flow clear despite the amount of rain received.