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Sewell Spring Branch (Reference Site)

About the site:

Consisting of a single site located on Sewell Spring Branch, a tributary to the Severn River, station SR-01 has a drainage area of approximately 574 acres. This site has been nearly continuously monitored since 2005. It is a mostly forested watershed (~60%) and has only about 10% impervious surface, most of which is disconnected. This site was established during geomorphic work performed for another project (Starr et al. 2010) and has become a de facto reference site for the County’s biological monitoring work.


2018 Summary Report:

Time FrameBIBI (Condition)FIBI (Condition)RBP (Condition)
2018 Results3.29 (Fair)3.00 (F)157 (Comparable)
Cumulative Average (2005-18)1 3.29 (Fair) 3.17 (F)150 (Supporting) 
3-year Running Average3.67 (Fair) 3.17 (F)153 (Comparable)
 1) No data for 2006.

Benthic IBI: 

Biological conditions at this station have been typically rated as Fair, with a long-term average BIBI of 3.29 and a three-year average score of 3.67. For 2018, a BIBI of 3.29 was obtained. Chironomids (non-biting midges) and caddisflies (moth-like insects) were the dominant insect groups observed during the 2018 sampling. In past years, blackflies and stoneflies were also commonly found in this location.

SR-01 Sample of Insects Collected by Sample Year

CY01 Bugs
Click to enlarge

Fish IBI: 

The FIBI indicates moderate ecological heath conditions. In 2018, a value of 3.00, or Fair, was obtained in this reach. Four species were observed at this location in 2016: American eel (Anguilla rostrata), eastern mudminnow (Umbra pygmaea), tessellated darter (Etheostoma olmstedi), and blacknose dace (Rhinchthys atratulus). The same species were observed during the sampling in 2016.  

Physical Habitat: 

Aquatic habitat conditions have also been very stable, with this site having a cumulative average RPB score in the Supporting range (150). Recent scores as reflected in the three-year average are even higher, falling into the Comparable to Reference category (153). High quality epifaunal substrate (structures on the streambed that provide surfaces on which animals can live), good distribution of pool depths and water velocities, low banks, and a broad forested riparian area all contribute to these conditions. These conditions remained largely unchanged between 2016 and 2018.

Stream Stability: Little change was observed from 2008 to 2010. In 2011, the channel elevation rose approximately 0.25 feet, but appeared to return to the 2010 elevation in 2012. The channel has steadily incised since 2012, with a maximum observed incision in 2017, resulting in a water elevation approximately 0.30 feet lower than that in 2012. The plot below shows this incision ending in 2018, causing an increase in stream elevation of approximately 0.40 feet. Overall, this stream has been relatively stable with little overall change in form since 2005.

SR-01 Cross Section Comparison 

Cross Section
Click to enlarge

Historical Data Summary:

YearBIBI (Condition)FIBI (Condition)RBP (Condition)
20053.00 (F)--128 (S)
20073.29 (F)--148 (S)
20083.29 (F)--134 (S)
20093.29 (F)--128 (S)
20102.71 (P)--160 (C)
20113.57 (F)--165 (C)
20122.14 (P)--170 (C)
20133.57 (F)--159 (C)
20143.57 (F)--160 (C)
20153.29 (F)3.33 (F)138 (S)
20163.86 (F)3.33 (F)140 (S)
20173.86 (F)--157 (C)
20183.29 (F)3.00 (F)159 (C)
Station Summary
 Average BIBI (SD)3-Year BIBI Average (SD)Average RBP (SD)3-Year RBP Average (SD)
SR-013.29 (0.47)3.67 (0.33)150 (14)153 (9)

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