855773644-LEED-v5-BD-C-Reference-Guide-Launch-Edition - Page 137

Extracted Content

• Average rainfall calculation . Calculate the average annual rainfall based on historical data. This can be done using methods like arithmetic means.

  • Monthly distribution . Distribute the average annual rainfall across months to create a representative year. This helps in understanding seasonal variations and planning for water management.

  • Runoff estimation . Use the average monthly rainfall data to estimate runoff for each month. This approach provides a simplified view of runoff patterns over a typical year.

By considering both the full range of hydrologic events and an average representative year, teams can develop a comprehensive understanding of stormwater runoff patterns and design an effective management system.

Runoff calculations Determine runoff volume using the rainfall event as calculated using Equation 1. Natural land hydrology, for this option, is the natural land cover present prior to any development on the site. Project teams must use the project’s natural land hydrology and land use to determine the runoff coefficient. For natural conditions, the runoff coefficient will be lower due to higher infiltration and vegetation cover.

Natural land cover refers to the original vegetation and soil conditions that existed in an area before any development or human activities altered the landscape.

By preserving or restoring natural land cover, projects can help to maintain ecological balance, support biodiversity, and enhance the sustainability of our environment.

Using the proposed design, calculate the design runoff, using the runoff coefficients for the design conditions as indicated in Option 1, Equation 1.

Retention requirements Projects must retain any increase in runoff within the project site. The retention design strategies in Table 2, LID/GI Measures, must mimic natural land hydrology.

Zero Lot Line Projects

For zero lot line projects, coordinate with regional authorities regarding off-site rainwater management strategies, which may be combined with on-site strategies to retain runoff for the required percentile. Off-site strategies must meet the credit intent of the LID/GI practices.

Given the limited space, it’s crucial to maximize the infiltration of stormwater on-site. This can be achieved through permeable pavements, green roofs, and rain gardens. Use underground

U.S. Green Building Council LEED v5 Reference Guide for Building Design and Construction, April 2025 Launch Edition 127