Method
Every number on this desk is derived, not asserted. This page states the conventions once so no article has to re-derive them. If a figure on any page disagrees with a convention below, the page is wrong; write us and it gets fixed with a dated correction.
1. Grade
Grade is rise over run, as a percent: grade % = (rise ÷ run) × 100. One percent means the ground falls 1 foot across 100 feet. A 4-foot level reads level when a 1% grade drops its downhill end by 0.48 inches — the thickness of a half-inch shim. We write grade as percent everywhere, never as ratio (20:1), because percent is what codes and inspectors use.
2. Percolation rate
Perk rate is inches of water level that drop per hour, from a single presoaked hole — the method in the perk test job. We report it as one number from one representative hole, and we say which hole. A yard is not a rate; one test hole is not a yard. That is a limitation the desk repeats on purpose.
3. Catchment
Catchment is square footage of impervious surface (roof planes, driveways, walks) plus the uphill yard area that visibly drains toward the wet spot — the counting rules in the catchment object. We use the plan-view footprint, not the pitched roof area, and we say so, because vendors often use the larger number.
4. Codes
Code figures (minimum grade, setback distances, drawdown limits) are always labeled as coming from a named code or stormwater manual, with a link. Codes differ between cities; a national number on a drainage page is a red flag. When we state a common range, we give the range, not a fake single value.
5. The stamp
Each page carries a checked date. Object and job pages are re-checked against their sources on that date. Note pages carry their writing date and a "rots" warning when the topic can decay. A stale stamp means the page has not been revisited, and the page says so.
Source ledger
Every document this desk draws from, linked to the exact page. A source appears here only after the desk has opened it.
- Minnesota Stormwater Manual (MPCA)
- Design criteria for wet swale (wetland channel) — swale geometry, sizing, and check-dam spacing
- Design criteria for infiltration — perk rates, drawdown limits, dry wells
- Infiltration — the four infiltration practice groups
- Check dams for stormwater swales — spacing, materials, and slope
- Sediment control practices: check dams, ditch checks — construction-phase ditch checks
- About the manual — scope and revision status
- US EPA
- NPDES stormwater program — the federal program municipal codes restate
- Stormwater discharges from municipal sources — MS4 permit obligations
- Stormwater discharges from construction activities — construction-phase controls
- Mosquito life cycle — the clock behind the 72-hour rule
- USDA NRCS — conservation practice standards
- Subsurface drain (code 606) — burial depth, bedding, outlets
- Critical area planting (code 342) — establishing vegetation on disturbed ground
- Grassed waterway (code 412) — vegetated channel capacity and velocity limits
- Conservation practice standards index — the standards this desk cites by code number
- USGS Water Science School
- Runoff: surface and overland water runoff — how water leaves a site
- Surface runoff and the water cycle — runoff as a share of rainfall
- Infiltration and the water cycle — what a perk rate means physically
- Groundwater storage and the water cycle — depth to groundwater and the frost line
- US CDC
- Life cycle of Aedes mosquitoes — egg-to-adult time in standing water
- Other federal sources
- 40 CFR 122.26 — Storm water discharges — the rule most municipal codes restate
- US FTC — Data security guidance for business — the standard the privacy page is written against
- Google Search Central — Creating helpful, reliable, people-first content — the content standard the four tests follow
Specific pages cite the subset they used. We do not quote documents from memory; a linked source means the desk opened that page on or before the stamped date.
Sources
- Minnesota Stormwater Manual — About the manual — supports the manual's design-criteria structure this desk follows.
- US EPA — NPDES stormwater program — supports the federal program the municipal codes restate.
- USDA NRCS — Conservation practice standards index — supports the practice standards this desk cites by code number.