Flood 2017 - Creek Impacts

The July 6 flood certainly had an impact on the creek.  Some sections lost all lose material right down to the bedrock.

Other sections accumulated material brought down from upstream.

Deposition of stone in the creek channel was due to the formation of debris dams that temporarily slowed the speed of the water.  As the water slowed, it lost the energy necessary to carry heavy objects and the gravel dropped out into the creek bed.

Water diverted out of the creek channel carried its sediment load along with it.  A number of sand bars were formed well away from the creek. 

Where the creek left its bed with more momentum, gravel bars were left behind.

There were even a few large flat rocks left stranded far from the creek.

At one bend in the creek the flood water cleaned the face of this bedrock arch.  This feature has never been so easy to view.

Water was deep enough that the meanders in the creek had little effect on the direction of flow.  The current went straight down hill, passing cleanly over every bend and curve in the creek channel.

It was not hard to tell in what direction the water was flowing.  I don’t think a steam roller could have laid these plants down any more than this.  This particular area typically has a nice floral display in late July.  I don’t think that’s going to happen this year.

In the broad, flat areas, water depth peaked at between two and three feet.  It’s going to take a couple of years before the visual effects of this flood event begin to disappear.

Flood Damage - Floodplain

Probably the most visible effects of the flood are in the floodplain where water doesn’t normally flow.  A flash flood through the steeply graded corridors of the upper watershed can strip away everything in its path.  The resulting bare ground is impossible not to notice.

The stream corridor is primarily wooded, so the ground cover is composed of scattered plants and a layer of decomposing leaf litter.  This is not the type of material that can withstand the force of speeding flood water.  Somewhere downstream, a quiet backwater has received a deposit of rich organic material that recently covered the floodplains of Blue Jay Barrens.

Floodplains don’t necessarily flood each year.  The areas near the bank of this meandering creek receive flood water on a regular basis, but the majority of the area hadn’t been underwater for decades.  This flood ignored the channel location and filled the valley.  For a few minutes, this quiet creek did its best to imitate a river.

It’s easy to find the bounds of the flood water.  Until a few days ago, the creek bank resembled the leaf covered hill in the background.  Now the only floodplain leaves that remain are those wrapped around the small trees and shrubs.  During the next couple of months I’ll find out what spring wildflowers remain to add stability and cover to the bare ground.

Flooding is a natural event and its occurrence is beyond my control.  I can return the damaged bridges to their previous state by collecting and reassembling the various parts, but there’s nothing I can do to fix the barren floodplains.  All I can do is watch and learn as natural processes work to restore the floodplain soils.

Areas that only experience a few inches of moving water should green up nicely and quickly hide the evidence of their ordeal.

Other areas will show their scars for some time to come.  It’ll be years before I can walk along the creek without seeing evidence of the record Flood of 2012.  Even so, the floodplains will green up through the summer and after the autumn leaves fall, much of the disturbance will be masked.  Dealing with uncontrollable events is probably the most frustrating part of land management.  I know there’s nothing I could have done to stop the flood, but that doesn’t keep me from being aggravated by the results.

Floodplain

This narrow strip of level floodplain area was the last field not near the house that was used for the production of annual crops. This was the largest area of deep soil to be found on the property and would have been a prime area for Burley Tobacco production. Its progression to a more natural ecosystem is progressing along an interesting course and I’m not sure where it will ultimately end. Despite a large number of deciduous trees scattered through the site, the area remains relatively open.

Green and White Ash are the dominant trees here. They are quite tall, but the trunks have a rather narrow diameter. This is typical of trees that begin life in a highly fertile soil. A typical tobacco field abandoned in the late 1970’s would have been left with an inflated level of fertility. Trees growing from these fields would have shown excessive growth through the pole stage and would have produced a stand of tall, thin trees.

Sycamores, growing along the bank of the creek, are much older and were in place and growing at the time the field was being cropped. These trees managed to avoid the die-backs that affected many Sycamores about 20 years ago.

Across the floodplain from the Sycamores are Honey Locusts that thrive where the base of the hill meets the level ground. Black Walnuts are the second most prominent tree on the floodplain. I don’t know whether or not the walnuts were naturally seeded or were planted as seedlings. The surrounding woods contain no walnuts that could have served as a seed source.

The Ash trees have been dieing at a rapid rate over the last ten years. This is also typical of trees that begin life in high fertility soils. It takes less root mass to support a tree under high fertility conditions, so the top outgrows the roots. When fertility levels begin to decrease, the roots have trouble expanding rapidly enough to keep the top growth from being stressed. The stress may kill the trees outright or it may allow the trees to fall victim to insect and disease invasions.

Another indicator of earlier high fertility conditions is the absence of cedars from the tree mix. Cedars quickly invade low fertility sites, but have trouble competing against vegetation that is boosted by high fertility. This section is completely free of cedars despite the fact that surrounding hillside areas show a heavy cedar growth.

The ground cover is primarily composed of species that have a broad range of light tolerance. I haven’t yet decided how this should be managed. As one tree grows to produce more shade, another dies to bring in more sunlight. As far as I can tell, this pattern will continue for quite some time. I guess I still have some time to study the area and decide on some management options before the site naturally evolves into something else.

Bridges vs. Floods

There hasn’t been any snow for awhile, but we’re far from getting any relief from the weather. Now we’re in a pattern of rain storms coming through every few days. Saturday’s storm dumped 3.4 inches of rain on top of already saturated soils and the resulting flash flood rose to set a new record. One of my concerns during times such as these is the security of my foot bridges spanning the creek.

After the record setting floods of 1997, this bridge was relocated and elevated to keep the bridge deck above the high water mark. The accumulation of debris shows that the bridge was submerged for at least part of the recent flood event. Fortunately, the flood water wasn’t strong enough to move it from this position.

This bridge didn’t fare quite as well. It looks a mess, but things aren’t really as bad as they appear.

The bridges are intended to move with the flood water. Each bridge is tethered to an immovable object. When the water rises, the bridges float up and lay themselves along the bank. The restraining cable can be seen attached to the lower right-hand corner of this bridge. Repositioning the bridge is much easier when it’s still at its proper site rather than a quarter mile down the creek.

My options in a situation like this are to either let the bridge move during a severe flood or elevate it above the high water level. Elevated bridges make it difficult to cross with DR Brush and still require maintenance of the approaches after a flood. Anchoring the bridge in place doesn’t work because the immobile bridge causes the creation of plunge pools, bank erosion and channel redirection such as you would get when a tree falls across the channel. Bridge movement is a rare occasion, so it’s not something I have to deal with very often.

At its peak, the flood water completely covered the level ground between the hills. The leaves that weren’t washed away, ended up plastered on the bases of the tree trunks. It’ll take a little while for the plants to upright themselves.

This bridge on a smaller tributary is intended to stay in place. The rock bottom of the stream is immune to plunge pool development and rock in the banks makes the whole site fairly stable. Strong storms are predicted through the middle of the week, so the bridges may get hit again. I’ll wait until things dry up a bit before putting things back where they belong.

Flowers of the Floodplain

I had a few minutes yesterday evening to walk back to the creek and see what was blooming. The nasty storms that came through the county last weekend missed us by several miles, so the creek didn’t flood. I’m glad. A flood this time of year really messes up the flower display. Fire Pink, Silene virginica, is just beginning to bloom. The red is so vibrant that it almost looks to be an artificial addition to the photo.

Blue Jay Barrens is located in the upper reaches of the watershed, so the floodplain is not typical of what most people imagine. It’s rare to have a rain intense enough to bring the water very far beyond the creek bank. When we do have a heavy rain, the flood event is extremely violent and only hours or sometimes minutes in duration. Smooth Phlox, Phlox glaberrima, doesn’t stand up to flood water. I think the pastel pink of the flower makes it the most beautiful of the phloxes.

This is one of the last of the Wild Comfrey, Cynoglossum virginianum, plants to bloom. When the hairy leaves begin to emerge early in the spring, I always think Common Mullein. That’s just a fleeting thought, though after seeing these plants in the same location for 25 years you would think I would just forget about mullein. These neat little petals are fused at the base and fall as a single unit after the flower is pollinated. The dropped blossoms look like party hats dropped by a crowd of New Year’s Eve revelers.

Wild Columbine, Aquilegia canadensis, is about at its peak right now. The floodplain soils are deep and well drained, with adequate moisture to growing conditions perfect for plants like this.

Great Wood Sorrel, Oxalis grandis, grows in the part of the floodplain that is least likely to sustain flood damage. This plant can get to be over two feet tall with leaves that stretch to two inches across. The yellow flower seems to be favored by butterflies and other insects. The leaves have a soft purple edge that almost seems fluorescent at times.

Flood Log

I found this short section of tree trunk on the floodplain near the creek. It was deposited here during a flood last January and given the frequency of flood events, will be carried away this year or next. Transient bits of debris such as this can develop their own little ecosystems full of special life forms.

Some life is carried along with the small log. This fungi, along with the mosses, lichens and even the slug, could have made the log their home at some point far upstream. Now in a new location, they continue to prosper.

A small bedstraw grows from the end of the log. When the log continues its journey down stream, the bedstraw will go with it and possibly found a colony of bedstraw in a new location. Riding the floodwaters is one way that organisms colonize new areas. Land managers have to be aware of conditions upstream and vigilantly inspect the floodplains for the arrival of possible invasive species.

Beneath the log are tunnels and chambers created by a colony of Lemon Scented Ants. The darker patches in the lower part of the picture are remnants of leaves that were covered by the log. I was really hoping to find a salamander under here, but that’s not likely to happen when ants have taken control.

The ants seem to have moved out of the log and down into the soil. If this is typical behavior, then they probably didn’t come from upstream and will be left in the soil when the log departs.

The creek makes a big S meander (no snickering please) at this point and the flood water jumps out and rushes overland in the direction I’m facing. Depending on the degree of flooding, the log’s next resting place could be one hundred to several thousand feet downstream. If it doesn’t go too far, I might be able to find it and see how that bedstraw survived the journey.