Sunday, July 1, 2007

July BMP Q&A

By: Jake Donellan, BMP Forester (Ret.), Texas Forest Service

Q:   It is starting to warm up now and it has become harder to tell whether or not streams need a SMZ (streamside management zone) or not. Are there any “rules of thumb” for knowing which streams ought to have a SMZ?

A:   It is important to remember that there are three general classifications of streams that are used in Texas: Perennial, intermittent, and ephemeral. Both perennial and intermittent streams should have a SMZ according to the Texas forestry BMP guidelines. Ephemeral streams do not necessarily need a SMZ but in some cases it is wise to leave some trees to buffer the stream especially if it is clear that the stream may erode or “wash” if nothing is left. This article will look specifically at ephemeral streams while the next couple of BMP Q& A articles will address perennial and intermittent stream classification in greater detail.

According to The American Heritage® Dictionary of the English Language, Fourth Edition, the term ephemeral is defined as, “adjective – lasting a very short time; short-lived; transitory.” By definition, ephemeral streams are streams that only last for a very short time. Ephemeral streams usually have a cumulative flow that is less than 30% of the year (about 3 ½ months). This normally equates to flow after rain events with the flow usually ending anywhere from immediately following the rain event to flow ending several days later.

During the dry summer months, identifying flow characteristics can often be difficult. If flow cannot be determined, the presence of three or more of the following characteristics should be helpful in recognizing an ephemeral stream:
  1. May have no well-defined channel
  2. The absence of water pools
  3. A flow area (channel) that is almost always straight and either “flattens” out at the bottom of the slope or grades into intermittent or perennial streams
  4. No or very little evidence of fluctuating high water marks (flood prone width) and/or sediment transport
  5. The presence of leaf litter and/or small debris jams in the flow area
  6. Usually sparse or no wetland (hydrophytic) vegetation present
  7. Side slope soils with characteristics typical of the surrounding landscape
  8. Usually not identified on USGS topographic maps or NRCS soil maps
These characteristics are found on page 62 of the Texas Forestry Best Management Practices book or “bluebook.”

You should rely on your professional judgment to determine when an ephemeral drain needs some type of protection in the form of a small SMZ or more simply a few buffer trees. These small streams are almost always connected to larger intermittent and perennial streams and severe erosion could enter the larger stream network if the ephemeral streams are not protected when necessary. For more information regarding BMPs consult the Texas Forestry Best Management Practices book, contact your local Texas Forest office, or you can contact me.

* This article was published in the July 2007 issue of the Texas Logger

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