Isolation and habitat alterations due to damming have been linked to significant declines in many North American fish and mussels over the last 50 years (Fausch et al. 2002; Pringel et al. 2000; Busch et al. 1998). In addition to blocking the movement of stream biota, dams significantly alter the biological, chemical, and physical properties of rivers. Water control and releases can significantly alter the timing, velocity, and volume of flows. In the artificial slack-water reservoir habitat behind dams, changes in the water temperature, chemical composition, dissolved oxygen levels, and physical habitat create conditions unsuitable to riverine biota. Reduction in sediment transport as particles are trapped behind dams also negatively affects downstream channel beds, floodplains, deltas, and coastal wetlands (Allan 1995).

Dams were a critical dataset in our Freshwater Resilience analysis and were compiled from multiple sources across CONUS. Dams on rivers (> 100 sq.km drainage area) were the focus of our connectivity modeling because inventories of smaller stream dams across CONUS are inconsistent and incomplete at present. In addition dams on rivers have a more significant effect on overall connectivity patterns as rivers are the conduits that connect smaller streams. For consistency, we defined rivers as flowlines with an upstream drainage area greater than 100 square kilometers (Wang et al. 2011).

Dams were compiled from 5 major sources:

1. Northeast Connectivity dams (NECON) (09Dec20 version) provided by TNC, E. Martin. Included the following states: VA, WV, PA, MD/DC, NJ, DE, NY, CT, RI, MA, VT, NH, and ME.

2. TNC California Field Office (CAFO) compiled dams for California’s Freshwater Resilience Analysis as of 1/18/2022 from the following sources: USGS National Anthropogenic Barrier dataset, California Passage Assessment Database September 2019 version, ODFW OR Fish Barrier Dataset 2019, and USFWS NV fish passage dataset 2019.

3. National Anthropogenic Barrier Dataset (NABD) Version 2 Beta. Updated as of 6/23/2020 NABDV2 (USGS, A. Cooper personal communication). This data was used in all states except those in the Northeast Connectivity Project or in CA where we had the above highly qc’ed recent data.

4. SARP Comprehensive Southeast Aquatic Barrier Inventory – Dams. Downloaded: 2022-04-14 from http://connectivity.sarpdata.com/. Included the following states: AL, AR, AZ, CO, FL, GA, IA, ID, IL, KS, KY, LA, MN, MO, MS, MT, NC, ND, NE, NM, NV, OK, SC, SD, TN, TX, UT, and WY.

5. Dams added by TNC staff during review

The original dam data sources were processed for quality control prior to use in our analysis. Primary steps included: 1) review spatial position and attributes of input dams, 2) snap dams to the NHDPlus flowline dendrites as appropriate, 3) further cross check and prioritize dams for manual review, 4) distribute dam data to TNC state chapters for internal and external expert review, and 5) reincorporate state edits into the final dataset. Key fields shared across datasets were populated, including national ids, dam name, state, owner type, height, storage volume, and primary purpose. Dams were coded as "partially passable" if they included a lock, had a fish passage facility, had a height greater than zero and less than two feet (height >0 and <2 ft.), and/or were identified as partially passable by members of the project steering committee.