Manure Storage Roof Savings (Covered vs Open)
The manure storage volume a roof buys back by keeping rainfall out of the pit.
Example
You enter
- Daily manure (ft3/day) 150
- Added bedding (ft3/day) 20
- Storage period (days) 120
- Surface / roof area (ft2) 8000
- Net precipitation over the period (in) 6
- 25-yr 24-hr storm depth (in) 4
- Freeboard (in: 6 vertical wall, 12 other) 12
You get
- Open facility volume 35067 ft3
- Volume a roof saves 6666.67
- Roof saving (gal) 49870.1
Checked against published worked examples from: USDA-NRCS Conservation Practice 313 (waste storage facility).
Details, formula, and sources
ScopeThe manure storage a roof buys back: roof_saving = area x (net_precip + storm)/12 - the whole rainfall term an open pit must bank on its own surface. An 8,000 ft2 pit in a 10-in wet season saves 6,667 ft3 (~50,000 gal, a fifth of the facility); a 12,000 ft2 pit in a wetter climate saves 15,000 ft3 (~112,000 gal, a third). The saving is clean rainwater the operation also avoids hauling and spreading, so a roof pays back fastest where it rains most. A planning aid, not the engineer of record.
Formula or tableopen = (daily_manure + wastewater + bedding) x days + area x (net_precip + storm)/12 + area x freeboard/12; roof_saving = area x (net_precip + storm)/12; covered = open - roof_saving; percent_saved = roof_saving / open x 100.
Source and editionManure storage covered-vs-open comparison (USDA-NRCS Conservation Practice 313 waste storage facility), by name.
Free accessNRCS Conservation Practice Standard 313 is public federal guidance; the engineer or planner governs the actual design.
What governsEstimate. AHJ and licensed professional govern.
API field namesdaily_manure_ft3, bedding_ft3, storage_days, surface_area_ft2, net_precip_in, storm_in, freeboard_in, open_ft3, roof_saving_ft3, roof_saving_gal
- Roof removes rain a roof eliminates the area x (net_precip + storm)/12 term the open facility carriesUSDA-NRCS 313
- Freeboard held equal freeboard is kept the same in both cases (conservative; a roofed structure can often carry less)USDA-NRCS 313