Application of the Natural Resources Conservation Service Technical Release 55 Method in Stormwater Management for Land Development Projects: A Practitioner Case Study

Citation: Anna Kyrytsia, "Application of the Natural Resources Conservation Service Technical Release 55 Method in Stormwater Management for Land Development Projects: A Practitioner Case Study", Universal Library of Engineering Technology, Volume 03, Issue 04.

Copyright: This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

The Natural Resources Conservation Service Technical Release 55 (TR-55) method remains one of the most widely used tools for estimating runoff on small land development sites in the United States, and in many Pennsylvania municipalities it is effectively the default method required for stormwater submissions. Most published work on the method concerns its theoretical basis, particularly the curve number and the initial abstraction ratio, while comparatively little describes how practicing engineers actually apply it and defend it in review. This paper documents that practice from the perspective of a civil engineer preparing site design and stormwater management plans for land development projects in Bucks County, Pennsylvania. It describes when the runoff calculation takes place in a typical project, how the principal inputs are selected (curve number from mapped hydrologic soil groups, time of concentration from segmented flow paths with a 100-foot sheet-flow limit, and rainfall depths from NOAA Atlas 14 checked against municipal ordinances), and how pre-development conditions are established on previously disturbed sites. These choices are then illustrated through one example from current practice: a townhouse development of approximately 3.5 acres, where the calculations led to two infiltration basins and a vegetated swale. The example shows how the hydrologic result meets the ordinance requirement, while site geometry, groundwater, infiltration rates, easements, utilities, and cost determine the final facility design. Review experience shows that stormwater submissions typically require two to three cycles, and that the most frequent comments concern time of concentration, curve number documentation, and the correspondence of drainage areas with the grading plan. Illustrative computations show why these inputs attract scrutiny: on small sites, modest changes in sheet-flow length, slope, or curve number shift peak discharge noticeably. The paper argues that many avoidable review cycles stem from inconsistent interpretation rather than from the method itself, and proposes a documentation standard for the assumptions reviewers most often question.

Keywords: Land Development, Municipal Review, Runoff Calculation, Stormwater Facilities, Stormwater Management.

https://doi.org/10.70315/uloap.ulete.2026.0304003