Difference between revisions of "Design infiltration rates"
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<!--{{alert|The original Manual had two different infiltration rates for B soils (0.3 and 0.6 inches per hour). In spring of 2013 the infiltration rate for all B soils was changed to 0.3 inches per hour. Following a meeting of technical experts on December 16, 2013, a rate of 0.45 inches per hour was established for SM soils.|alert-warning}}--> | <!--{{alert|The original Manual had two different infiltration rates for B soils (0.3 and 0.6 inches per hour). In spring of 2013 the infiltration rate for all B soils was changed to 0.3 inches per hour. Following a meeting of technical experts on December 16, 2013, a rate of 0.45 inches per hour was established for SM soils.|alert-warning}}--> | ||
| − | <font size=3>'''Design infiltration rates, in inches per hour, for A, B, C, and D soil groups. Corresponding USDA soil classification and Unified soil Classifications are included. Note that A soils have two infiltration rates that are a function of soil texture.*'''</font size><br> | + | <font size=3>'''Design infiltration rates, in inches per hour, for A, B, C, and D soil groups. Corresponding USDA soil classification and Unified soil Classifications are included. Note that A soils have two infiltration rates that are a function of soil texture.*''' The values shown in this table are for uncompacted soils. [https://stormwater.pca.state.mn.us/index.php?title=General_relationship_of_soil_bulk_density_to_root_growth_based_on_soil_texture This table] can be used as a guide to determine if a soil is compacted. For information on alleviating compacted soils, [https://stormwater.pca.state.mn.us/index.php/Alleviating_compaction_from_construction_activities link here]. If a soil is compacted, reduce the soil infiltration rate by one level (e.g. for a compacted B(SM) use the infiltration rate for a B(MH) soil).</font size><br> |
Link to this [[Design infiltration rates|table]] | Link to this [[Design infiltration rates|table]] | ||
<table class="sortable"><tr> | <table class="sortable"><tr> | ||
Revision as of 18:48, 9 April 2018
Design infiltration rates, in inches per hour, for A, B, C, and D soil groups. Corresponding USDA soil classification and Unified soil Classifications are included. Note that A soils have two infiltration rates that are a function of soil texture.* The values shown in this table are for uncompacted soils. This table can be used as a guide to determine if a soil is compacted. For information on alleviating compacted soils, link here. If a soil is compacted, reduce the soil infiltration rate by one level (e.g. for a compacted B(SM) use the infiltration rate for a B(MH) soil).
Link to this table
| Hydrologic soil group | Infiltration rate (inches/hour) | Infiltration rate (centimeters/hour) | Soil textures | Corresponding Unified Soil Classification |
|---|---|---|---|---|
| 1.63a | 4.14 |
gravel |
GW - well-graded gravels, sandy gravels |
|
| 0.8 | 2.03 |
sand |
SP - gap-graded or uniform sands, gravelly sands |
|
| 0.45 | 1.14 | SM - silty sands, silty gravelly sands | ||
| 0.3 | 0.76 | loam, silt loam | MH - micaceous silts, diatomaceous silts, volcanic ash | |
| 0.2 | 0.51 | Sandy clay loam | ML - silts, very fine sands, silty or clayey fine sands | |
| 0.06 | 0.15 |
clay loam |
GC - clayey gravels, clayey sandy gravels |
*NOTE that this table has been updated from Version 2.X of the Minnesota Stormwater Manual. The higher infiltration rate for B soils was decreased from 0.6 inches per hour to 0.45 inches per hour and a value of 0.06 is used for D soils (instead of < 0.2 in/hr).
Source: Thirty guidance manuals and many other stormwater references were reviewed to compile recommended infiltration rates. All of these sources use the following studies as the basis for their recommended infiltration rates: (1) Rawls, Brakensiek and Saxton (1982); (2) Rawls, Gimenez and Grossman (1998); (3) Bouwer and Rice (1984); and (4) Urban Hydrology for Small Watersheds (NRCS). SWWD, 2005, provides field documented data that supports the proposed infiltration rates. (view reference list)
aThis rate is consistent with the infiltration rate provided for the lower end of the Hydrologic Soil Group A soils in the Wisconsin Department of Natural Resources Conservation Practice Standard: Site Evaluation for Stormwater Infiltration.