Dividing Creek (DC-01 and DC-02)

a) Fish data were collected 2015, 2016, 2018, 2020, and 2022. 

a) Fish data were collected 2015, 2016, 2018, 2020, and 2022. 

Site DC-01: The site is located on Anne Arundel Community College property, just upstream of the College Parkway road crossing. The site’s 2023 BIBI score was 2.71 (Poor).  BIBI scores at this site have been categorized as “Poor” or “Very Poor” every year since sampling began in 2010.  The 2023 sample was dominated by flies, which comprised over 50% of all organisms found. Caddisflies were present in the sample for the fourth consecutive year.

DC-01 Summary of Insects Collected by Sample Year:

Site DC-02: This site is also located on Anne Arundel Community College property, upstream of DC-01 and just downstream of West Campus Drive.  While technically within the footprint of the restoration project completed in 2016, the sampling reach was unaltered by construction activity, therefore sampling persisted throughout the construction period. The sampling reach is situated between two areas where the stream channel was reconfigured into a series of riprap steps and large pools typical of a wetland seepage system. While not purposely converted into a pool area, the sampling site has experienced an increase in water depth, and velocity has slowed due to the impacts of the downstream pool area. At its upstream end, the sampling reach includes a constructed stone weir (a dam that raises water level) that created a pool just upstream of the site.

This site received a BIBI score of 1.57 (Very Poor) in 2023. The site has been in the “Poor” or “Very Poor” categories for 12 of the 14 years it has been sampled (it received a “Fair” rating in 2010 and 2015).  The 2023 sample was dominated by flies, which accounted for approximately 85 percent of all organisms. Caddisflies were absent from the sample for the second consecutive year.

While the sample reach itself was not included in the construction activities, stream reaches above and below the sampling reach were dramatically altered by the restoration project. The impact that a particular stream restoration project has on reaches downstream of the restoration is not well understood. However, it is possible that the restoration work has had impacts on both sample reaches. It is also possible that an unknown water quality impairment originating upstream has caused this shift at one or both stations. The ultimate trajectory and persistence of any supposed change will require continued long-term sampling at these locations.

DC-02 Summary of Insects Collected by Sample Year:

Site DC-01: The site received a FIBI score of 2.33 (Poor) in 2022. Four species were observed in 2020: eastern mosquitofish (Gambusia holbrooki), American eel (Anguilla rostrata), eastern mudminnow (Umbra pygmaea), and golden shiner (Notemigonus crysoleucas).  The proportion of eastern mosquitofish, the dominant species in the 2022 sample, has increased each sampling event since 2018, while eastern mudminnow representation has decreased by nearly 70% since 2016.

DC-01 Summary of Fish Collected by Sample Year:

Site DC-02: DC-02 received a FIBI score of  2.67 (Poor) in 2022. The same four species were observed at DC-02 as were found at DC-01 (eastern mosquitofish, American eel, eastern mudminnow, golden shiner), though eastern mosquitofish and eastern mudminnows were more evenly distributed at DC-02.

DC-02 Summary of Fish Collected by Sample Year:

Site DC-01: In 2023, a habitat score of 133 (Supporting) was calculated for this site.  Habitat conditions have been fairly consistent since monitoring began here in 2010, earning a “Supporting” rating in all but two years.  High levels of bank stability and vegetative cover, diversity of channel flow features, and little evidence of channel alteration all contribute to the high quality habitat observed here.

Site DC-02: Habitat scores have been consistent here since 2015 and indicate some improvement since monitoring commenced here in 2010. In 2023, an RBP score of 114 (Partially Supporting) was calculated, the lowest the site has scored since 2014.  Still, habitat quality at the site has remained fairly consistent, scoring as “Partially Supporting” or “Supporting” in 12 out of 14 years.

Site DC-01: A new cross section was established for this site in 2017, due to the loss of the previous years’ monuments. The establishment of a new cross section made it impractical to directly compare pre-and post-restoration geomorphology. The prior examination of the cross section (2010 - 2016) showed little alteration between 2015 and 2016. However, the site appeared to experience significant sediment inputs between the 2011 and 2012 measurements, as the thalweg elevation rose approximately 0.8 feet over that period. Elevations in-channel remained the same for 2013, but steady incision between 2013 and 2016 resulted in the removal of approximately half of the in-channel sediment inputs observed in 2011 and 2012. Additionally, steady erosion of the right bank (downstream) and deposition on the left bank was noticeable between 2010 and 2016, resulting in a channel that appeared to be shifting towards the right bank while maintaining its approximate cross-sectional area as it progressed. The current cross-section comparison shows little overall change between 2017 and 2023 other than slight aggradation of the stream channel. Attempts in future years to relocate the old monuments will be made when sampling, but if they are unable to be found, the 2017 established monuments will be used for all future comparisons.

DC-01 Cross-Section Comparison:

Site DC-02: While the banks at DC-02 appear to be relatively stable, the channel bottom looks to be less so.  Between 2010 and 2021 the channel bottom incised by approximately 1.7 feet, but nearly one foot of sediment was deposited on the channel bottom between 2021 and 2022. However, as sediment retention is a stated objective of this restoration approach, this sort of aggradation is to be expected at this site.

DC-02 Cross-Section Comparison:

Historical Data Summary:

SD = Standard Deviation