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Minnesota Stormwater Manual

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}}-->
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{{alert|The table for design infiltration rates has been modified. Field testing is recommended for gravelly soils (HSG A; GW and GP soils; gravel and sandy gravel soils). If field-measured soil infiltration rates exceed 8.3 inches per hour, the Construction Stormwater permit requires the soils be amended. Guidance on amending these soils [[Guidance for amending soils with rapid or high infiltration rates|can be found here]].|alert-warning}}
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<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 and B soils have two infiltration rates that are a function of soil texture.*'''<br>
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'''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>
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Link to this [[Design infiltration rates|table]]
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<table class="sortable"><tr>
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<th>Hydrologic soil group</th>
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<th>Infiltration rate (inches/hour)</th>
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<th>Infiltration rate (centimeters/hour)</th>
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<th>Soil textures</th>
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<th>Corresponding Unified Soil Classification</th>
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</tr>
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<tr>
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<tr>
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<td rowspan="3"><center>A</center></td>
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<td colspan="2">Although a value of 1.63 inches per hour (4.14 centimeters per hour) may be used, it is '''''Highly recommended''''' that you conduct field infiltration tests or amend soils.<sup>b</sup> See [[Guidance for amending soils with rapid or high infiltration rates]] and [https://stormwater.pca.state.mn.us/index.php?title=Determining_soil_infiltration_rates Determining soil infiltration rates].</td>
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<td>
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gravel<br>
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sandy gravel
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</td>
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<td>GW - well-graded gravels, sandy gravels<br>
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GP - gap-graded or uniform gravels, sandy gravels</td>
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</tr>
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<tr>
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<td>1.63<sup>a</sup></td>
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<td>4.14</td>
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<td>
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silty gravels<br>
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gravelly sands<br>
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sand
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</td>
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<td>
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GM - silty gravels, silty sandy gravels<br>
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SW - well-graded gravelly sands<br>
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SW - uniformly graded sands
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</td>
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</tr>
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<tr>
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<td>0.8</td>
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<td>2.03</td>
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<td>
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sand<br>
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loamy sand<br>
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sandy loam
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</td>
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<td>
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SP - gap-graded or poorly graded sands
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</td>
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</tr>
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<tr>
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<td rowspan="2"><center>B</center></td>
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<td>0.45</td>
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<td>1.14</td>
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<td></td>
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<td>SM - silty sands, silty gravelly sands</td>
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</tr>
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<tr>
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<td>0.3</td>
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<td>0.76</td>
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<td>loam, silt loam</td>
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<td>MH - micaceous silts, diatomaceous silts, volcanic ash</td>
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</tr>
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<tr>
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<td><center>C</center></td>
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<td>0.2</td>
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<td>0.51</td>
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<td>Sandy clay loam</td>
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<td>ML - silts, very fine sands, silty or clayey fine sands</td>
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</tr>
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<tr>
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<td><center>D</center></td>
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<td>0.06</td>
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<td>0.15</td>
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<td>
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clay loam<br>
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silty clay loam<br>
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sandy clay<br>
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silty clay<br>
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clay
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</td>
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<td>
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GC - clayey gravels, clayey sandy gravels<br>
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SC - clayey sands, clayey gravelly sands<br>
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CL - low plasticity clays, sandy or silty clays<br>
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OL - organic silts and clays of low plasticity<br>
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CH - highly plastic clays and sandy clays<br>
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OH - organic silts and clays of high plasticity
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</tr>
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</table>
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<font size=1>*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).<br>
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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. ([[References|view reference list]])<br>
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<sup>a</sup>This rate is consistent with the infiltration rate provided for the lower end of the Hydrologic Soil Group A soils in the [http://dnr.wi.gov/topic/stormwater/documents/dnr1002-infiltration.pdf Wisconsin Department of Natural Resources Conservation Practice Standard: Site Evaluation for Stormwater Infiltration].<br>
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<sup>b</sup>The infiltration rates in this table are recommended values for sizing stormwater practices based on information collected from soil borings or pits. A group of technical experts developed the table for the original Minnesota Stormwater Manual in 2005. Additional technical review resulted in an update to the table in 2011. Over the past 5 to 7 years, several government agencies revised or developed guidance for designing infiltration practices. Several states now require or strongly recommend field infiltration tests. Examples include North Carolina, New York, Georgia, and the City of Philadelphia. The states of Washington and Maine strongly recommend field testing for infiltration rates, but both states allow grain size analyses in the determination of infiltration rates. The Minnesota Stormwater Manual strongly recommends field testing for infiltration rate, but allows information from soil borings or pits to be used in determining infiltration rate. A literature review suggests the values in the [https://stormwater.pca.state.mn.us/index.php?title=Design_infiltration_rates design infiltration rate table] are not appropriate for soils with very high infiltration rates. This includes gravels, sandy gravels, and uniformly graded sands. Infiltration rates for these geologic materials are higher than indicated in the table.<br>
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References
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*Clapp, R. B., and George M. Hornberger. 1978. Empirical equations for some soil hydraulic properties. Water Resources Research. 14:4:601–604.
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*Moynihan, K., and Vasconcelos, J. 2014. [https://www.chijournal.org/Journals/PDF/C372 SWMM Modeling of a Rural Watershed in the Lower Coastal Plains of the United States]. Journal of Water Management Modeling. C372.
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*Rawls, W.J., D. Gimenez, and R. Grossman. 1998. Use of soil texture, bulk density and slope of the water retention curve to predict saturated hydraulic conductivity Transactions of the ASAE. VOL. 41(4): 983-988.
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*Saxton, K.E., and W. J. Rawls. 2005. Soil Water Characteristic Estimates by Texture and Organic Matter for Hydrologic Solutions. Soil Science Society of America Journal. 70:5:1569-1578.
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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}}
  
 
<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=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.*'''
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Revision as of 17:40, 31 July 2018

Caution: The table for design infiltration rates has been modified. Field testing is recommended for gravelly soils (HSG A; GW and GP soils; gravel and sandy gravel soils). If field-measured soil infiltration rates exceed 8.3 inches per hour, the Construction Stormwater permit requires the soils be amended. Guidance on amending these soils can be found here.

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 and B 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
A
 Although a value of 1.63 inches per hour (4.14 centimeters per hour) may be used, it is Highly recommended that you conduct field infiltration tests or amend soils.b See Guidance for amending soils with rapid or high infiltration rates and Determining soil infiltration rates.

gravel
sandy gravel

GW - well-graded gravels, sandy gravels
GP - gap-graded or uniform gravels, sandy gravels
1.63a 4.14

silty gravels
gravelly sands
sand

GM - silty gravels, silty sandy gravels
SW - well-graded gravelly sands
SW - uniformly graded sands

0.8 2.03

sand
loamy sand
sandy loam

SP - gap-graded or poorly graded sands

B
 0.45 1.14 SM - silty sands, silty gravelly sands
0.3 0.76 loam, silt loam MH - micaceous silts, diatomaceous silts, volcanic ash
C
 0.2 0.51 Sandy clay loam ML - silts, very fine sands, silty or clayey fine sands
D
 0.06 0.15

clay loam
silty clay loam
sandy clay
silty clay
clay

GC - clayey gravels, clayey sandy gravels
SC - clayey sands, clayey gravelly sands
CL - low plasticity clays, sandy or silty clays
OL - organic silts and clays of low plasticity
CH - highly plastic clays and sandy clays
OH - organic silts and clays of high plasticity

*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.
bThe infiltration rates in this table are recommended values for sizing stormwater practices based on information collected from soil borings or pits. A group of technical experts developed the table for the original Minnesota Stormwater Manual in 2005. Additional technical review resulted in an update to the table in 2011. Over the past 5 to 7 years, several government agencies revised or developed guidance for designing infiltration practices. Several states now require or strongly recommend field infiltration tests. Examples include North Carolina, New York, Georgia, and the City of Philadelphia. The states of Washington and Maine strongly recommend field testing for infiltration rates, but both states allow grain size analyses in the determination of infiltration rates. The Minnesota Stormwater Manual strongly recommends field testing for infiltration rate, but allows information from soil borings or pits to be used in determining infiltration rate. A literature review suggests the values in the design infiltration rate table are not appropriate for soils with very high infiltration rates. This includes gravels, sandy gravels, and uniformly graded sands. Infiltration rates for these geologic materials are higher than indicated in the table.
References

  • Clapp, R. B., and George M. Hornberger. 1978. Empirical equations for some soil hydraulic properties. Water Resources Research. 14:4:601–604.
  • Moynihan, K., and Vasconcelos, J. 2014. SWMM Modeling of a Rural Watershed in the Lower Coastal Plains of the United States. Journal of Water Management Modeling. C372.
  • Rawls, W.J., D. Gimenez, and R. Grossman. 1998. Use of soil texture, bulk density and slope of the water retention curve to predict saturated hydraulic conductivity Transactions of the ASAE. VOL. 41(4): 983-988.
  • Saxton, K.E., and W. J. Rawls. 2005. Soil Water Characteristic Estimates by Texture and Organic Matter for Hydrologic Solutions. Soil Science Society of America Journal. 70:5:1569-1578.
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