Reviewed September 22, 2026. Wrivel favors government and standards-body sources for technical context; product marketing is not used to set calculation constants.
NOAA / National Weather Service
Hydrometeorological Design Studies Center (HDSC) — official precipitation-frequency estimates and NOAA Atlas products for U.S. areas. Current-status note (reviewed September 21, 2026): NOAA identifies Atlas 14 as the current authoritative precipitation-frequency standard where it applies; HDSC still lists current legacy publications for areas not covered by Atlas 14. Atlas 15 is the next-generation update and remains in development. Use the applicable current NOAA publication and any controlling local design standard when selecting a storm.
USDA Natural Resources Conservation Service — Roof Runoff Structure 558
Roof Runoff Structure (558) — official NRCS practice material for collecting, controlling and conveying roof runoff. NRCS explicitly states that national conservation-practice standards set the baseline and that the adopted state Field Office Technical Guide should be used for planning and design because state criteria may be more restrictive. The current NRCS index lists national Roof Runoff Structure 558 with an issue date of July 2021.
USDA NRCS — catchment-area geometry
NRCS Engineering Field Handbook, Subpart T — its rainwater-catchment guidance says to estimate roof catchment area using the horizontal footprint of the structure. Wrivel follows that geometry for roof-runoff volume.
USDA NRCS — Stormwater Runoff Control 570
Stormwater Runoff Control (570) — official NRCS stormwater-runoff practice material. The current NRCS index lists the national standard with an issue date of September 2020, and the same state/local adoption caveat applies.
US EPA — field infiltration / percolation context
Saving the Rain: Green Stormwater Solutions describes a homeowner-oriented percolation check: pre-wet a test hole, refill it, and observe the repeat drain-down; that guide uses complete drainage within 36 hours as its simple rain-garden screen. EPA's Semi-Arid Green Infrastructure Toolbox — Rain Gardens separately cites 0.5 in/hr as a general infiltration-rate reference for a rain garden expected to drain in roughly 6–12 hours. These are separate screening/design contexts, not interchangeable tests. Wrivel does not assume that water-level drop in a simple test hole equals saturated hydraulic conductivity or a formal design infiltration rate; local test methods and design criteria govern.
US EPA — stormwater drainage wells
Stormwater Drainage Wells explains that dry wells and other subsurface infiltration systems can fall under Class V underground-injection requirements depending on configuration and jurisdiction. This is why Wrivel does not treat a favorable field drain-down observation as legal approval to install a dry well.
What is calculated rather than sourced
The 0.6233766 gallons factor is a unit conversion. Wrivel's lawn coefficients and example 40% stone-void assumption are openly labeled planning scenarios; they are not presented as universal code values.
Why Wrivel does not auto-import a “local answer”
Rainfall, soil, setbacks and drainage rules are jurisdiction-specific. Keeping those inputs visible avoids presenting a generic online estimate as a permit-ready local design.