Indicator: Network Complexity

Aug 10, 2020 (Last modified Aug 27, 2020)
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This indicator depicts the number of different stream size classes in a river network not separated by large dams.

Reason for Selection

River networks with a variety of connected stream classes help retain aquatic biodiversity in a changing climate by allowing species to access climate refugia and move between habitats.

Input Data

– Estimated Floodplain Map of the Conterminous U.S. from the EPA EnviroAtlas (see this factsheet for more information)

– Other input for this indicator was provided by the Southeast Aquatic Connectivity Assessment Project (SEACAP). SEACAP identifies this metric within the category of “size/system type”. It measures the number different stream size classes in each functional network. To be counted, the stream size must be > 0.5 miles long (final SEACAP report, page 97). To create the spatial component of this layer, the number of stream sizes is applied to the estimated floodplain inside the functional network.

Stream size classes are defined as:

1a: Headwaters (< 3.861 sq mi)

1b: Creeks (≥ 3.861 and < 38.61 sq mi)

2: Small Rivers (≥ 38.61 and < 200 sq mi)

3a: Medium Tributary Rivers (≥ 200 and < 1000 sq mi)

3b: Medium Mainstem Rivers (≥ 1000 and < 3861 sq mi)

4: Large Rivers (≥ 3861 and < 9653 sq mi)

5: Great Rivers (≥ 9653 sq mi)

Mapping Steps

1) SEACAP calculated this measure by counting the number of different stream size classes in each functional network.

2) We intersected the functional network layer with the EPA estimated floodplain layer in order to spatially apply this metric to the estimated floodplain.

3) We converted to 30 m cell size using the Resample function in ArcGIS with the majority resampling technique.

Final indicator values

Indicator values were assigned as follows:

7 = 7 connected stream classes (high)

6 = 6 connected stream classes

5 = 5 connected stream classes

4 = 4 connected stream classes

3 = 3 connected stream classes

2 = 2 connected stream classes

1 = 1 connected stream class (low)


Functional Network:

SEACAP developed linear spatial data on the presence of priority diadromous species. These layers are modified versions of the NHDPlus Version 2. These data were altered to contain presence of Alabama Shad using data from the Atlantic States Marine Fisheries Commission (produced for the ASMFC by the Biodiversity and Spatial Information Center at North Carolina State University, Alexa Mckerrow), and expert knowledge of the SEACAP Workgroup.

Functional Catchments:

SEACAP also developed a functional river network layer (final SEACAP report, page 9). A functional river network is a network is defined by those stream reaches that are accessible to a hypothetical fish within that network. The functional river network is defined by lines (streams). SEACAP also calculated “functional catchments,” which are polygons that represent the catchment area that is associated with each of those functional networks.

Estimated Floodplain map:

The EPA Estimated Floodplain Map of the Conterminous U.S. displays “…areas estimated to be inundated by a 100-year flood, also known as the 1% annual chance flood. These data are based on the Federal Emergency Management Agency (FEMA) 100-year flood inundation maps with the goal of creating a seamless floodplain map at 30-meter resolution for the conterminous United States. This map identifies a given pixel’s membership in the 100-year floodplain and completes areas that FEMA has not yet mapped.”

Known Issues

– Does not account for smaller dams/culverts.

– May not include other smaller scale attributes of complexity (e.g., sinuosity, mixtures of riffles/pools/runs).

– The barrier assessment used in this indicator was last updated in 2014. Given the extensive work on aquatic connectivity in the Southeast, this indicator likely underestimates connected stream classes in some areas.

– The EPA Estimated Floodplain layer sometimes misses the small, linear connections made by artificial canals, especially when they go through areas that wouldn’t naturally be part of the floodplain. As a result, some areas (like lakes) that are connected via canals may appear to be disconnected, but still receive high scores.

–This indicator does not account for the habitat quality of the connections.

–While this indicator generally includes the open water area of reservoirs, some open water portions of Kerr Lake are missing from the estimated floodplain dataset.

Disclaimer: Comparing with Older Indicator Versions

There are numerous problems with using South Atlantic indicators for change analysis. Please consult Blueprint staff if you would like to do this (email

Literature Cited

Martin, E. H, Hoenke, K., Granstaff, E., Barnett, A., Kauffman, J., Robinson, S. and Apse, C.D. 2014. SEACAP: Southeast Aquatic Connectivity Assessment Project: Assessing the ecological impact of dams on Southeastern rivers. The Nature Conservancy, Eastern Division Conservation Science , Southeast Aquatic Resources Partnership.

EPA EnviroAtlas. 2018. Estimated Floodplain Map of the Conterminous U.S.

Data Provided By:
generated using ADIwg mdTranslator 2.17.1
Data Hosted by:
ScienceBase (USGS) View Record
Map Service URL:
Content date:
2020-08-15 04:00:00 (lastRevision Date), 2020-08-15 04:00:00 (Release Date), 2019-08-15 04:00:00 (Start Date), 2021-08-15 04:00:00 (End Date)
Rua Mordecai(Point of Contact), Amy Keister(Point of Contact), Hilary Morris(Point of Contact), U.S. Fish and Wildlife Service(Point of Contact), Southeast Conservation Adaptation Strategy (SECAS)(Point of Contact), 2020-08-15(lastRevision), 2020-08-15(Release), Indicator: Network Complexity,,
Contact Organization:
Southeast Conservation Adaptation Strategy (SECAS)
U.S. Fish and Wildlife Service
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The South Atlantic Conservation Blueprint is a living spatial plan to conserve natural and cultural resources for current and future generations in the face of future change. It spans parts of six states, from Virginia to Florida, including U.S. waters to 200 miles offshore. The Blueprint...