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REFERENCE DOCUMENTS

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TABLE OF CONTENTS REFERENCE DOCUMENTS REFERENCE DOCUMENT A: MEAN SEASONAL PRECIPITATION MAP R 1 REFERENCE DOCUMENT B: K FACTOR R 2 REFERENCE DOCUMENT C: RUNOFF COEFFICIENT C FACTOR R 3 REFERENCE DOCUMENT D: HYDROLOGIC SOIL GROUPS R -4 REFERENCE DOCUMENT E: SAMPLE STRUCTURAL SOIL SPECIFICATION R 5 REFERENCE DOCUMENT F: STRUCTURAL SOIL REFERENCE INFORMATION R 12 Low Impact Development Technical Design Manual

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REFERENCE DOCUMENT A MEAN SEASONAL PRECIPITATION MAP City of Santa Rosa and County of Sonoma

REFERENCE DOCUMENT B K FACTOR Low Impact Development Technical Design Manual

REFERENCE DOCUMENT B 2.5 2.5 2.0 2.0 1.5 1.5 1.0 1.0 0.5 0.5 K FACTOR K = MEAN SEASONAL PRECIPITATION DIVIDED BY 30 10 20 30 40 50 60 70 80 MEAN SEASONAL PRECIPITATION - INCHES Page R-2 PROVIDED BY THE SONOMA COUNTY WATER AGENCY

REFERENCE DOCUMENT C RUNOFF COEFFICIENT C FACTOR City of Santa Rosa and County of Sonoma

REFERENCE DOCUMENT C 6 Runoff Reduction Areas 6.1 Design Philosophy Using alternative surfaces with a lower coefficient of runoff or C-Factor helps reduce runoff from developed areas. The C-Factor is a representation of a surface s ability to produce runoff. Surfaces that produce higher volumes of runoff are represented by higher C-Factors, such as impervious surfaces. Surfaces that produce smaller volumes of runoff are represented by lower C-Factors, such as more pervious surfaces. See Table 6-1 for typical C-Factor values for various surfaces during small storms. Pervious Concrete Pervious Asphalt Turf Block Brick (un-grouted) Natural Stone Concrete Unit Pavers Table 6-2 compares the C-Factors of conventional paving surfaces to alternative, lower C-Factor paving surfaces. By incorporating more pervious, lower C-Factor surfaces into a development, lower volumes of runoff are produced. Lower volumes and rates of runoff translate directly to lower treatment requirements. Site design techniques may be used to reduce the C- Factor of a developed area, reducing the amount of runoff requiring treatment, including: Crushed Aggregate Cobbles Wood Mulch Other site design techniques such as disconnecting impervious areas, preservation of natural areas, and designing concave medians may be used to reduce the overall C-Factor of development areas. Table 6-1 Estimated C-Factors for Various Surfaces During Small Storms Paving Surface Concrete Asphalt Pervious Concrete Cobbles Pervious Asphalt Natural Stone without Grout Turf Block Brick without Grout Unit Pavers on Sand Crushed Aggregate Grass Grass Over Porous Plastic Gravel Over Porous Plastic C-Factor 0.80 0.70 0.60 0.60 0.55 0.25 0.15 0.13 0.10 0.10 0.10 0.05 0.05 Note: C-Factors for frequent small storms used to size water quality BMPs are likely to differ (be lower) than C-Factors developed for infrequent, large storms used to size flood control facilities. The above C-Factors were produced by selecting the lower end of the best available C-Factor range for each paving surface. These C-Factors are only appropriate for small storm treatment design, and should not be used for flood control sizing. Where available, locally developed small storm C-Factors for various surfaces should be utilized. Page R-3 Provided by BASMA

REFERENCE DOCUMENT D HYDROLOGIC SOIL GROUPS Low Impact Development Technical Design Manual

REFERENCE DOCUMENT D Appendix B Hydr Synt ologic het ic Soil Rainfall Gr oups Dist r ibut ions and Rainfall Dat a Sour ces Ex hi bi t A: Hydr ol ogi c Soil Gr oups f or t he Uni t ed St at es Soils are classified into hydrologic soil groups (HSG s) Di st u r b ed so il p r o f iles to indicate the minimum rate of infiltration obtained for The bare highest soil after peak prolonged discharges wetting. from The small HSG watersheds s, which in are the United As a States result are of urbanization, usually caused the by soil intense, profile brief may rainfalls A, B, that C, and may D, occur are one as element distinct events used in or determining as part of a longer storm. siderably These altered intense and rainstorms the listed do group not usually classification ex- may be contended runoff curve over numbers a large area (see and chapter intensities 2). For vary the greatly. convenience synthetic of TR-55 rainfall users, distribution exhibit A-1 to use lists in the lieu HSG of classifi- actual storm events. ing to This determine distribution HSG according includes maximum to the texture rainfall of the One common no longer practice apply. in rainfall-runoff In these circumstances, analysis is use to develop the follow- a intensities cation of United for the States selected soils. design frequency arranged in a sequence new surface that is soil, critical provided for producing that significant peak runoff. compaction has not occurred (Brakensiek and Rawls 1983). Syn The infiltration t h et i c rate r ainf is the all rate at d which i st r iwater b u t enters i o n sthe soil at the soil surface. It is controlled by surface conditions. length HSG also of the indicates most intense the transmission rainfall period rate contributing the rateto the peak runoff rate is related to the time of concentration which (Tthe c ) for water the moves watershed. within In the a hydrograph soil. This rate created is with NRCS Aprocedures, Sand, th loamy sand, or sandy loam HSG Soi l textures The controlled by the soil profile. Approximate numerical B Silt loam or loam ranges for transmission rates shown in the HSG definitions were first published by Musgrave (USDA 1955). C Sandy clay loam D Clay loam, silty clay loam, sandy clay, silty The four groups are defined by SCS soil scientists as clay, or clay follows: Gr oup A soils have low runoff potential and high infiltration rates even when thoroughly wetted. They consist chiefly of deep, well to excessively drained sand or gravel and have a high rate of water transmission (greater than 0.30 in/hr). Gr oup B soils have moderate infiltration rates when thoroughly wetted and consist chiefly of moderately deep to deep, moderately well to well drained soils with moderately fine to moderately coarse textures. These soils have a moderate rate of water transmission (0.15-0.30 in/hr). Gr oup C soils have low infiltration rates when thoroughly wetted and consist chiefly of soils with a layer that impedes downward movement of water and soils with moderately fine to fine texture. These soils have a low rate of water transmission (0.05-0.15 in/hr). Gr oup Dsoils have high runoff potential. They have very low infiltration rates when thoroughly wetted and consist chiefly of clay soils with a high swelling potential, soils with a permanent high water table, soils with a claypan or clay layer at or near the surface, and shallow soils over nearly impervious material. These soils have a very low rate of water transmission (0-0.05 in/hr). In exhibit A-1, some of the listed soils have an added modifier; for example, Abrazo, gravelly. This refers to a gravelly phase of the Abrazo series that is found in SCS soil map legends. Dr ainage an d gr o u p D so ils Some soils in the list are in group D because of a high water table that creates a drainage problem. Once these soils are effectively drained, they are placed in a different group. For example, Ackerman soil is classified as A/D. This indicates that the drained Ackerman soil is in group A and the undrained soil is in group D. Page R-4

REFERENCE DOCUMENT E SAMPLE STRUCTURAL SOIL SPECIFICATIONS City of Santa Rosa and County of Sonoma

REFERENCE DOCUMENT E CU-Soil Specification and Mixing Procedure CU-Soil is a patented material and must be purchased from a licensed supplier. Amereq (http://www.amereq.com/) licenses the manufacturing of CU-Soil to ensure quality control of installations. Page R-5

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