Pond Assessment Tool 1.1 is Ready

UPDATES: September 2025 | Volume 20, Issue 1

Contributed by Poornima Natarajan, Ben Janke, Jacques Finlay, & John Gulliver

The Challenge

Thousands of ponds are used for stormwater management in Minnesota cities, providing the crucial function of runoff detention and removal of phosphorus (P) and other pollutants, mitigating risks of eutrophication of receiving water. As many ponds are now decades old, their treatment performance may degrade from accumulating organic matter and encroachment of vegetation, leading to low oxygen and sedimentary P release. Assessment of pond performance to evaluate the status of existing ponds is needed to determine if management and maintenance could improve function but comprehensive monitoring of stormwater inflows and outflows is expensive, time-consuming, and not a practical option for most watershed managers given the large number of ponds in many cities. Therefore, a substantial need exists to assess the performance of Minnesota’s numerous ponds for P removal in a relatively robust, straightforward, and inexpensive manner.  

What We Did

To this end, the Local Road Research Board (LRRB) and the Minnesota Stormwater Research Council (MSRC) funded projects at the St. Anthony Falls Laboratory, University of Minnesota, to develop a spreadsheet-based Pond Assessment Tool (Janke et al. 2023; Natarajan et al. 2025), built on the results of several years of intensive data collection (water samples, water chemistry, sediment phosphorus release, aggregation and characterization of supporting datasets) through multiple research projects funded by MSRC, LRRB, and others. We have developed an understanding of pond and landscape factors (“risk indicators”) that are strongly associated with high surface water P concentrations and with anoxic sediment P release in ponds treating stormwater. The Tool (Figure 1) predicts water column total phosphorus (TP) concentrations and sediment P release rates using regression equations and includes capacity to predict pond oxygen status (extent of anoxia), a parameter specifically important for sediment P release. The Tool also provides simpler assessment methods relying on classifying levels of risk indicators, i.e., factors such as floating and emergent plant coverage, surrounding soil and land use, and tree canopy cover, which are derived from readily available spatial data, aerial photos, pond drawings, or direct observation, but that do not require extensive sample collection or analysis. 

What you can do

The Pond Assessment Tool is made for stormwater practitioners to use. The Tool supports assessment of many ponds quickly, with results intended to inform monitoring or maintenance strategies for pond P management, and early versions of the Tool have been well-received by potential users, consisting of MnDOT staff as well as city, county and consulting staff scientists and engineers. The Tool is developed to be easily updated and expanded to realize its potential as a robust and useful screening and assessment method for identifying stormwater ponds in need of further study, maintenance, or other management, especially for phosphorus. Future versions of the Tool could be adapted to address hydrologic functions, other pollutants in stormwater, and incorporate impacts of retrofits or design practices (e.g., weir skimmers, sand filter benches).

References

• Hein, D., Strecker E., Poresky A., Roseen R. 2013. Permeable shoulders with stone reservoirs. Report prepared from the American Association of State Highway and Transportation Officials (AASHTO), NCHRP Project 25-25, Task 82, National Cooperative Highway Research Program, Transportation Research Board.
• Janke, B.D., Natarajan, P., Gulliver, J.S, and Finlay, J.C. 2023. Stormwater pond maintenance, and wetland management for phosphorous retention. Final report to the Minnesota Department of Transportation, Minneapolis, MN. https://hdl.handle.net/11299/256430
• Natarajan, P., Janke, B.D., and Finlay, J.C. 2025. Enhancement and Validation of a Stormwater Pond Assessment Tool. Final report to the Minnesota Stormwater Research Council, Project Report No. 610, St. Anthony Falls Laboratory, University of Minnesota, Minneapolis, MN. https://hdl.handle.net/11299/273518

Other Resources Available at SAFL’s Stormwater Website

In addition to the Pond Assessment Tool, there are four additional resources available in the Resources page.  These are:

Siting Surface Infiltration-Based SCMs (Funded by the LRRB): A GIS tool developed to help with Siting Surface Infiltration-Based Stormwater Control Measures Using a Geographic Information Systems Approach. A preliminary infiltration rating (PIR) was developed as a composite rating calculated in a geographic information system to assess the likelihood of success of a future surface infiltration-based stormwater BMP at a given location. The input variables to the PIR include soils data obtained from the Natural Resources Conservation Service (NRCS) Soil Survey Geographic Database (SSURGO) data set, which provides a hydrologic soil rating (A through D) and a depth to the water table. SSURGO data are available for approximately 92% of the counties in the United States of America and territories as of November 2019. Information relating to the presence of wetlands, shallow bedrock, karst features, and drinking water supply management areas are all included in the environmentally sensitive areas layer overlaid on the PIR. An example demonstration is given in Figure 2. The PIR can serve as an effective planning tool for siting future surface infiltration-based BMPs in the land development process and can guide a site-specific investigation. 

Find it on our Resources Page.

References: https://doi.org/10.1061/JSWBAY.0000940 and https://www.cts.umn.edu/publications/report/design-and-construction-of-infiltration-facilities

Roadside Swale Calculator (Funded by the LRRB): The Roadside Swale Calculator is a spreadsheet calculator that is used to compute the infiltration that occurs at roadside swales. Information on annual precipitation, road width, width from the road to the swale bottom and an estimate of saturated hydraulic conductivity are needed. The calculator and the ancillary information provided can be used to determine: (1) the total percentage of annual volume infiltrated, (2) the percentage of events entirely captured by a roadside swale in a year, and (3) the percentage of road runoff infiltrated by a roadside swale with a specific swale width-to-road width ratio and saturated hydraulic conductivity for a given rainfall depth event. An example of possible calculations is provided in Figure 3. 

Find it on our Resources Page.

References: https://doi.org/10.1061/(ASCE)HE.1943-5584.0001650 and https://mdl.mndot.gov/items/201615

MNPavePerm (Funded by the LRRB): MNPavePerm is a spreadsheet tool that allows users to determine whether permeable pavement is appropriate for their specific site and project characteristics. Based upon a program developed under NCHRP (Hein et al. 2013), it has been adjusted for conditions common to Minnesota. An example application of MNPavePerm is given in Figure 4. 

Find it on our Resources Page.

References: https://doi.org/10.1080/10298436.2017.1279482 and http://www.lrrb.org/media/reports/201530.pdf

Visual Inspection Checklists (Funded by the Minnesota Pollution Control Agency & Local Road Research Board of MN): Standardized inspection and maintenance guidance, including visual inspection checklists to allow for quick, simple, visual assessment of stormwater treatment practices. These visual inspection checklists can be downloaded into most software and can serve as a basis to develop checklists specific to one region. 

Find it on our Resources Page.

References: Gulliver, J.S., A.J. Erickson, and P.T. Weiss (editors). 2010. "Stormwater Treatment: Assessment and Maintenance. University of Minnesota, St. Anthony Falls Laboratory. Minneapolis, MN. https://stormwaterbook.safl.umn.edu/ and Erickson, A.J., P.T. Weiss, and J.S. Gulliver. 2013 "Optimizing Stormwater Treatment Practices: A Handbook of Assessment and Maintenance." ISBN 978-1-4614-4623-1. Springer Publishing, New York, NY.