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Chesapeake Bay

SWAT+ modeling in the Chesapeake Bay watershed

SWAT+ models for USGS stream gauges and watersheds in the Bay's four regions, built on NHDPlus HR.

Start with a Bay watershed

Our models in the Bay

USGS 01595000, a Potomac test gaugeUSGS 01595500, a Potomac test gaugeUSGS 01595800, a Potomac test gaugeUSGS 01596500, a Potomac test gaugeUSGS 01597500, a Potomac test gaugeUSGS 01598500, a Potomac test gaugeUSGS 01599000, a Potomac test gaugeUSGS 01601000, a Potomac test gaugeUSGS 01601500, a Potomac test gaugeUSGS 01603000, a Potomac test gaugeUSGS 01604500, a Potomac test gaugeUSGS 01605500, a Potomac test gaugeUSGS 01606000, a Potomac test gaugeUSGS 01606500, a Potomac test gaugeUSGS 01607500, a Potomac test gaugeUSGS 01608000, a Potomac test gaugeUSGS 01608500, a Potomac test gaugeUSGS 01609000, a Potomac test gaugeUSGS 01610155, a Potomac test gaugeUSGS 01611500, a Potomac test gaugeUSGS 01614000, a Potomac test gaugeUSGS 01614500, a Potomac test gaugeUSGS 01615000, a Potomac test gaugeUSGS 01616500, a Potomac test gaugeUSGS 01619500, a Potomac test gaugeUSGS 01622000, a Potomac test gaugeUSGS 01625000, a Potomac test gaugeUSGS 01626000, a Potomac test gaugeUSGS 01627500, a Potomac test gaugeUSGS 01628500, a Potomac test gaugeUSGS 01629500, a Potomac test gaugeUSGS 01631000, a Potomac test gaugeUSGS 01632000, a Potomac test gaugeUSGS 01632082, a Potomac test gaugeUSGS 01632900, a Potomac test gaugeUSGS 01633000, a Potomac test gaugeUSGS 01634000, a Potomac test gaugeUSGS 01634500, a Potomac test gaugeUSGS 01635500, a Potomac test gaugeUSGS 01636316, a Potomac test gaugeUSGS 01637500, a Potomac test gaugeUSGS 01638350, a Potomac test gaugeUSGS 01638420, a Potomac test gaugeUSGS 01638480, a Potomac test gaugeUSGS 01639000, a Potomac test gaugeUSGS 01639500, a Potomac test gaugeUSGS 01642190, a Potomac test gaugeUSGS 01643000, a Potomac test gaugeUSGS 01643500, a Potomac test gaugeUSGS 01643700, a Potomac test gaugeUSGS 01643805, a Potomac test gaugeUSGS 01643880, a Potomac test gaugeUSGS 01644000, a Potomac test gaugeUSGS 01644280, a Potomac test gaugeUSGS 01645000, a Potomac test gaugeUSGS 01646000, a Potomac test gaugeUSGS 01649500, a Potomac test gaugeUSGS 01650500, a Potomac test gaugeUSGS 01651000, a Potomac test gaugeUSGS 01653000, a Potomac test gaugeUSGS 01653600, a Potomac test gaugeUSGS 01654000, a Potomac test gaugeUSGS 01656000, a Potomac test gaugeUSGS 01658000, a Potomac test gaugeUSGS 01660400, a Potomac test gaugeUSGS 01660920, a Potomac test gaugeUSGS 01661500, a Potomac test gaugeBig Elk Creek at Elk Mills, MD (USGS 01495000)Lycoming Creek near Trout Run, PA (USGS 01550000)Bixler Run near Loysville, PA (USGS 01567500)Kerrs Creek near Lexington, VA (USGS 02022500)Wapwallopen Creek near Wapwallopen, PA (USGS 01538000), being builtLittle Gunpowder Falls at Laurel Brook, MD (USGS 01584500), being builtJohns Creek at New Castle, VA (USGS 02017500), being built
Example models you can openModels being built for this pageGauges in the Potomac test set (not models)

Model outputs

Bixler Run near Loysville, PA (USGS 01567500), calibrated against its USGS gauge

05101520252012201320142015
Daily flow, 2012 to 2015 (m³/s): the calibrated model and the USGS gauge (grey). These are verification years: the calibration was fitted to other years.

Over these years: daily NSE 0.75, KGE 0.79, and PBIAS +2.3 % (the model simulates 2.3 % more water than the gauge measured).

From the applied calibration's verification row, key 9c23f9a2-0a29-4c55-ab40-a7d5b0ddc28e.

The same calibrated run's average annual water balance, 2012 to 2015 (mm per year, rounded to whole mm):

Precipitation1002 mm
Evapotranspiration614 mm
Surface runoff141 mm
Lateral flow65 mm
Percolation196 mm
Change in soil water-13 mm

Open the model

Lycoming Creek near Trout Run, PA (USGS 01550000), calibrated against its USGS gauge

01002003004002005200620072008200920102011201220132014201520162017
Daily flow, 2005 to 2017 (m³/s): the calibrated model and the USGS gauge (grey). These are verification years: the calibration was fitted to other years.

Over these years: daily NSE 0.63, KGE 0.71, and PBIAS -4.8 % (the model simulates 4.8 % less water than the gauge measured).

From the applied calibration's verification row, key 9956ad1d-5193-479d-b9c8-b735a940b316.

The same calibrated run's average annual water balance, 2005 to 2017 (mm per year, rounded to whole mm):

Precipitation1057 mm
Evapotranspiration468 mm
Surface runoff338 mm
Lateral flow31 mm
Percolation225 mm
Change in soil water-4 mm

Each calibration is fitted to its own gauge, on request; each chart shows one model's result.

Calibration against your gauge · Open the model

Our other Bay models

  • Wapwallopen Creek near Wapwallopen, PA · USGS 01538000 · gauge drainage area 113.4 km² · Not offered: no channel at the gauge, so no flow chart
  • Little Gunpowder Falls at Laurel Brook, MD · USGS 01584500 · gauge drainage area 93.5 km² · Not offered: no channel at the gauge, so no flow chart
  • Big Elk Creek at Elk Mills, MD · USGS 01495000 · gauge drainage area 133.6 km² · Open the model
  • Johns Creek at New Castle, VA · USGS 02017500 · gauge drainage area 271.9 km² · Not offered: no channel at the gauge, so no flow chart
  • Kerrs Creek near Lexington, VA · USGS 02022500 · gauge drainage area 90.9 km² · Open the model

NHDPlus HR, not Version 2: the network our models are built on

020,00040,00060,00080,000100,000020,00040,00060,00080,000100,000NHDPlus Version 2.1, kmNHDPlus HR, kmSusquehanna River BasinUpper ChesapeakePotomacLower ChesapeakeLower ChesapeakeSusquehanna River BasinPotomacUpper Chesapeake
Each point is one basin (WBD HUC4): its network flow paths in NHDPlus Version 2.1 (across) and in NHDPlus HR (up), filled with canals and ditches in both counts, hollow without them. On the line, the two would be equal. Ringed: the two datasets' areas for this basin differ by more than 5 %: Upper Chesapeake.

On the 53 Bay HUC8 subbasins that both datasets carry, NHDPlus HR maps 233,690 km of network flow paths, against 128,240 km in NHDPlus Version 2.1: 1.82 times as much, about 105,000 km more.

NHDPlus HR divides the same land into 439,492 catchments, against 83,631: one for every 0.39 km² on average, against one for every 2.04 km².

Explore each basin

Susquehanna River Basin

Our models: Lower West Branch Susquehanna · USGS 01550000 (Lycoming Creek near Trout Run); Lower Susquehanna-Swatara · USGS 01567500 (Bixler Run near Loysville)

Upper Chesapeake

Our model: Chester-Sassafras · USGS 01495000 (Big Elk Creek at Elk Mills)

A model of your Bay watershed

We build a SWAT+ model for a USGS stream gauge in the Bay's four regions, on NHDPlus HR. You download it as files you open in SWAT+ Editor and run, and you keep the files.

Free, $0, to try it on a real station. Starter, $50 / month USD. MAX, $100 / month USD. Cloud calibration is pay as you go, on every plan including Free.

See the plans and order
The Bay's modelling programmes, data and our registered test

The Chesapeake Bay watershed spans four hydrologic regions (HUC4 0205 to 0208), from the Susquehanna to the James.

Chesapeake Bay Program, Phase 6 Watershed Model. Each river with at least 100 cubic feet per second of average flow is a separate reach and river segment; smaller streams enter through factors from SPARROW on NHDPlus version 1.1. Sources: Phase 6 documentation, Physical Setting (2018), p. 3 · Phase 6 documentation, Land to Water (2018), p. 3

Chesapeake Bay Program, Phase 7 (in development). Its 2025 progress slides show "A 1st order NHD MR stream" as an example of its stream network. Delivery of the model suite for partnership review was moved to 1 January 2027. Sources: Phase 7 progress slides (2025), p. 17 · Phase 7 model development · Phase 7 timeline, PSC, 20 August 2025, p. 4

Chesapeake Bay Program catchment layer. The Bay Program publishes a modified NHDPlus Version 2.1 catchment layer at 1:100,000 with 83,628 catchments. Sources: CBP catchment layer, item information

National Water Model v2.1. Its daily streamflow at Bay gauges is scored gauge by gauge in a published benchmark study (Towler et al., 2023), which our registered test below uses for the incumbent. Sources: Towler et al. (2023), HESS 27, 1809

Published SWAT+ work in the Bay. A SWAT+ model with groundwater flow (gwflow) of the Nanticoke River, published in Hydrology and Earth System Sciences in 2024. Sources: HESS 28, 21-48 (2024)

What the Bay community asks for, in its own words: “Specific needs include better regional/sub-watershed models, more localized information about groundwater inputs” (STAC report (2023), p. 17); “it does not reflect localized high-loss areas at field or farm scale” (CESR report (2023), p. 56).

Of the Bay's 56 HUC8 subbasins, 3 are carried by one dataset only and are left out of these figures.

A finer network exists too: a 1-meter lidar stream network for the Bay was released in 2025 (doi:10.5066/P1GRAPEX). Its authors describe "non-trivial amounts of error" in what they call their initial attempt. Data release

958 Bay stream gauges are known to our station list; 519 have any daily flow record, and 306 have daily flow with at most 20 % of days missing.

4 published example models sit in the Bay's four regions today. USGS 01495000, USGS 01550000, USGS 01567500, USGS 02022500

Our default SWAT+ build, uncalibrated, at 67 gauges in the Potomac River basin, against the National Water Model v2.1 on the same days (2015-01-01 to 2020-12-31), scored by daily KGE at each gauge.

The rules that decide the outcome, including when a comparison may be stated in our favour, were written down before any of the test models was built. The result is pending, and this page will show it as measured.