Q: In June you described several key attributes or criteria to help to identify ephemeral streams. Can you provide similar identifiable attributes or criteria for intermittent streams?
A: Certainly, it is important to remember that there are three general classifications of streams that are used to describe streams: 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 intermittent streams while the next BMP Q& A article will address perennial stream classification in greater detail.
Dictionary.com defines, the term “intermittent” as an adjective: “stopping or ceasing for a time; alternately ceasing and beginning again” Because water flow in intermittent streams can start and stop several times during a year, this is a great definition to describe the characteristics of intermittent streams. Intermittent streams have seasonal flow usually 30% to 90% of the year (3 ½ months to 10 ½ months) under normal climatic conditions.
This interpretation of intermittent streams means that a large majority of streams fall into this category. All that is required for a stream to be considered intermittent is for it to have some flow for 3 ½ months cumulatively during a year. So if a stream only flows during the wet winter months from November to February is it an intermittent? The answer in this case would be YES, since that equates to 4 months and all that is required is 3 ½ months. The same result would occur if this stream were to flow for two months in the spring and then again for two months in the winter.
During the dry summer months, however, identifying flow characteristics can often be difficult. If flow cannot be determined, the presence of five or more of the following characteristics should be helpful in recognizing an intermittent stream:
- Well-defined channel.
- Water pools absent during dry conditions but present during wet conditions.
- A channel that is mostly sinuous (winding or curvy).
- Some evidence of fluctuating high water marks (flood prone width) and/or sediment transport, also the indication of a flood zone parallel to the stream by sediment deposits, sediment stained leaves, bare ground and/or drift lines.
- Evidence of soil and debris movement (scouring) in the stream channel. Leaf litter is usually transient or temporary in the flow channel.
- Wetland or hydrophytic vegetation is usually associated with the stream channel or flow area
- Predominately brown soils with inclusions of gray soils (except soils of deep sands with extreme red soil color). Usually alluvial type soils with loamy to sandy texture.
- Usually identified on USGS topographic maps as a thin blue line or a blue line separated by three dots or identified on a NRCS soil maps as a black line separated by two or more dots.
- Intermittent streams are considered “Waters of the United States” and therefore fall under the jurisdictional limits of the authority of the U.S. Army Corps of Engineers under the Clean Water Act.
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 September 2007 issue of the Texas Logger