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2 Appendix F: Sample Calculations & Worksheets Intentionally Le Blank DEELOPMENT BEST MANAGEMENT PRACTICES HANDBOO Part B: PLANNING ACTIITIES, 5 TH ED.

Appendix F: Sample Calculations & Worksheets FLOW RATE AND OLUME CALCULATION EXAMPLE olume must be calculated for each tributary area to size each BMP.

3 Appendix F: Sample Calculations & Worksheets FLOW RATE AND OLUME CALCULATION EXAMPLE olume must be calculated for each tributary area to size each BMP. PROJECT NAME: Commercial Site (Intersection of Western Ave & Washington Blvd) Provide proposed project characteristics ATotal Type of Development 1.15 Acres Commercial Flow Path Length 00 Flow Path Slope.01 (1%) % of Project Impervious 87 % Predominate Soil Type # 1 Storm * 85 th percentile *Projects are required to use the larger of the Stormwater Quality Storm. The volume of runoff produced from a 0.75 inch (or ) storm event, or The 85 th percentile, 4- runoff event at this location 1.1 inch (or 0.91 ) Refer to LA County Hydrology GIS Map DETERMINING THE PEA MITIGATED FLOW RATE (QPM): Download HydroCalc Calculator (save onto your desktop). The HydroCalc Calculator allows the site designer/engineer to calculate runoff rates and volumes from the water quality storm. DEELOPMENT BEST MANAGEMENT PRACTICES HANDBOO Part B: PLANNING ACTIITIES, 5 TH ED.

4 DETERMINING THE OLUME (M) Appendix F: Sample Calculations & Worksheets In order to determine the volume (M) of stormwater runoff to be mitigated from the new development, use the larger storm volume from the following equation(s): 0.75 in Storm: M ( ) ( 0.65 Ft ) Catchment Area (Sq. Ft) 85 th Percentile Storm: M ( ) (Storm Depth (Ft ) ) Catchment Area (Sq. Ft) From Example, 1.1 inch > 0.75 inch, use 1.1 inch (0.91) Storm: AI 1.0 acres Refer to LA County Hydrology GIS Map and Probability_Analysis_of_85th_Percentile_4-_Rainfall1.pdf AP 0.15 acres M ( ) ( ) Catchment Area (in ) Catchment area ( ( impervious area 0.9) + [( pervious area + undeveloped ) 0.1] 4,560 1 ac [ 0.15 ac 0.1] 9,857.4 ) area [( ) ( ) ] Catchment area M ( ) ( ) 9,857.4 ( ) M,67 (verify results with Hydrocalc results) BMP TYPE AND SIZE 10. List the BMP Type(s) to be used in managing the calculated m, and size it per the design criteria listen in Section 4. The following examples have been provided as a reference: Infiltration BMPs: Infiltration Trench Dry Well Infiltration Basin Capture and Use Rain Tanks Above / Below Grade Cisterns Biofiltration egetated Swale Planter Box Biofiltration with underdrain DEELOPMENT BEST MANAGEMENT PRACTICES HANDBOO Part B: PLANNING ACTIITIES, 5 TH ED.

5 Infiltration BMP - for At Grade Infiltration Trench Appendix F: Sample Calculations & Worksheets m,67 (from previous step) Measured in/ (Do not apply LA County reduction factor) T 48 s (from Table 4.4) FS (from Table 4.4) Gravel void ratio 40% i. Determine Measured FS in in ii. Determine Minimum Bottom Infiltration, A min : A min m 1in Sat, T,67 1in A 0.667in / 48 min 1, 59 iii. Determine - infiltration volume, - : 1in 0.667in 1in Amin s 1,59 s 6 iv. Determine the volume stored within the trench, Trench Storage : oid ratio, m Trench Storage 9,067 v. Determine remaining volume of storage required: Storage 9, , 841 Trench Storage vi. Determine Depth: D A 8,841 Storage min 1, DEELOPMENT BEST MANAGEMENT PRACTICES HANDBOO Part B: PLANNING ACTIITIES, 5 TH ED.

6 Infiltration BMP for Below Grade Dry Well Appendix F: Sample Calculations & Worksheets m,67 (from previous step) Measured in/ (Do not apply LA County reduction factor) Gravel void ratio 40% Factor of Safety (per table 4.4) A min 94 D 6 (r ) i. Required dry well depth for the infiltration zone, h: h A πr πr min h * * Multiple dry wells may be used to achieve the equivalent infiltration zone. ii. Determine the dry well storage volume, Storage : (assuming entirely filled with gravel) Storage Dry Well DryWell oid [ r ] 0. 4 Ratio π h [ π ( ) 48 ] iii. Determine - infiltration volume, - : 1in 0.667in 1in Amin s 94 s 156 iv. Determine the additional required storage volume, Additional Storage : ( + ),67 ( ), m 98 Additional Storage Storage Drw Well,98 of additional storage is required. In order to satisfy the additional storage requirement, an upstream cistern or additional dry well chambers can be used. Some proprietary systems may provide additional storage capacity. Coordinate with manufactures. DEELOPMENT BEST MANAGEMENT PRACTICES HANDBOO Part B: PLANNING ACTIITIES, 5 TH ED.

7 Appendix F: Sample Calculations & Worksheets Infiltration BMP for Below Grade Infiltration Basin m,67 (from previous step) Measured in/ (Do not apply LA County reduction factor) T 96 s (Table 4.4) i. Determine the design infiltration rate, : in Measured in FS ii. Determine Minimum Bottom Infiltration, A min : A min m 1in T sat,,67 1in A 0.667in / 96 min 680 iii. Determine the Basin, D Basin : D A, Storage Ba sin 5. min DEELOPMENT BEST MANAGEMENT PRACTICES HANDBOO Part B: PLANNING ACTIITIES, 5 TH ED.

8 Appendix F: Sample Calculations & Worksheets for: Capture & Use,67 (from previous step) 0.15 acres of pervious area Medium Planting Type Planting Factor 0.4 i. Determine the design volume in gallons: gal gal ( ), , 10 gal ii. Determine planting area ( ) within project limits: Planting Area ( ) 0.15 ac 4,560 6,54 ac iii. Determine Planter Factor, PF, ( ): (Planting factor may vary based on landscape design and plant types. Coordinate with Landscape Architect.) Planter Factor ( ) 0.4 6,54,614 iv. Determine the 7- month (Oct 1 April 0) Estimated Total Water Use (ETWU): ETWU ( 7 month ) ET PF ETWU month ,614 5, 16 ( 7 ) gal v. erify ETWU (7-month) is greater than or equal to the ed : ETWU ( 7 month) ) 5,16 gal ( gal), 67 gal CAPTURE & USE IS FEASIABLE DEELOPMENT BEST MANAGEMENT PRACTICES HANDBOO Part B: PLANNING ACTIITIES, 5 TH ED.

9 Appendix F: Sample Calculations & Worksheets Biofiltration BMP for egetated Swale* base of swale 5 Slope % i. Determine the swale base width and corresponding unit length: Per Table 4.6 Select swale base of 5 with corresponding unit length of 470 /ac. ii. Determine the total swale length: 1 acre LSwale ).5 Catchment area ( ) 4,560 ( 1 Catchment area ( Catchment area ( Swale lenght per catchment area ( impervious area 0.9) + [( pervious area + undeveloped ) 0.1] ) area ) 4,560 [( 1 0.9) + [( ) 0.1] ] ( / acre) Catchment area ( ) 9, acre LSwale ( ) 1.5 9, / acre 4,560 L Swale ( ) 645 iii. Determine the distance between check dams: Per Table 4.7 At a % slope, the distance between check dams is. iv. Determine total number of check dams: Total 645 # of dams 19.5 use 0 * Depending on the location of the swale, a geotechnical report may need to be submitted and approval from LADBS may be required. DEELOPMENT BEST MANAGEMENT PRACTICES HANDBOO Part B: PLANNING ACTIITIES, 5 TH ED.

10 Appendix F: Sample Calculations & Worksheets for: Planter Box m,67 (from previous step) Soil media infiltration rate, k sat : 5 in/ (Table 4.5) Time to fill of media (4 soil, 1 gravel) to ponding depth, T Fill s (Table 4.5) (per engineer, ex: 4 soil media, 1 gravel) Drawdown time, T () 48 s (Table 4.5) Ponding Depth 1 (MAX) (Table 4.5) i. Determine the design volume: ( ) 1. 5 m ( ) 1.5,67 5,440 ii. Determine the design infiltration rate, : 5 in Media in. 5 FS iii. Calculate the BMP Surface Area, A min *: 5,440 Amin ( ), 47 s.5 in TFill k d + 1 p 1 in + 1 in * Rule of thumb: With a max ponding depth of 1, area needed is 5-6% of impervious area DEELOPMENT BEST MANAGEMENT PRACTICES HANDBOO Part B: PLANNING ACTIITIES, 5 TH ED.

11 Appendix F: Sample Calculations & Worksheets Alternative I If ponding depth is reduced to 6 (0.50 ), and the planting media is maintained at 4 and 1 of washed gravel, the minimum planter surface area would then be as follows: m,67 (from previous step) Soil media infiltration rate, k sat : 5 in/ (Table 4.5) Time to fill of media (4 soil, 1 gravel) to ponding depth, T Fill s (Table 4.5) (per engineer, ex: 4 soil media, 1 gravel) Drawdown time, T () 48 s (Table 4.5) Ponding Depth, d p () (Table 4.5) i. Determine the design volume: ( ) 1. 5 m ( ) 1.5,67 5,440 ii. Determine the design infiltration rate, : 5 in Media in. 5 FS iii. Calculate the BMP Surface Area, A min : 5,440 Amin ( ) 4, 85 T k.5 in Fill d p in + 1 in DEELOPMENT BEST MANAGEMENT PRACTICES HANDBOO Part B: PLANNING ACTIITIES, 5 TH ED.

12 Appendix F: Sample Calculations & Worksheets Alternative II If ponding depth is reduced to (0.5 ) and planting media and gravel section total height are proposed to be 4 ( ), the minimum planter surface area would then be as follows: m,67 (from previous step) Soil media infiltration rate, k sat : 5 in/ (Table 4.5) Time to fill media (18 soil, 6 gravel) to ponding depth, T Fill s (Table 4.5) (per engineer: 18 soil media, 6 gravel) Drawdown time, T () 48 s (Table 4.5) Ponding Depth, d p () (MIN) 0.5 (Table 4.5) i. Determine the design volume: ( ) 1. 5 m ( ) 1.5,67 5,440 ii. Determine the design infiltration rate, : 5 in Media in. 5 FS iii. Calculate the BMP Surface Area, A min : 5,440 Amin ( ) 8, 160 T k.5 in Fill d p in + 1 in DEELOPMENT BEST MANAGEMENT PRACTICES HANDBOO Part B: PLANNING ACTIITIES, 5 TH ED.

13 Appendix F: Sample Calculations & Worksheets for: Biofiltration with underdrain (at grade) m,67 (from previous step) Soil media infiltration rate, k sat : 5 in/ (Table 4.5) Time to fill of media (4 soil, 1 gravel) to ponding depth, T Fill s (Table 4.5) (per engineer, ex: 4 soil media, 1 gravel) Drawdown time, T () 48 s (Table 4.5) Ponding Depth 15 in. (per engineer, 18 in max) (Table 4.5) Side slopes :1 iv. Determine the design volume: ( ) 1. 5 m ( ) 1.5,67 5,440 v. Determine the design infiltration rate, : 5 in Media in. 5 FS vi. Calculate the BMP Surface Area, A min *: 5,440 Amin ( ),901. s.5 in TFill k d p 1 in + 1 in DEELOPMENT BEST MANAGEMENT PRACTICES HANDBOO Part B: PLANNING ACTIITIES, 5 TH ED.

At least 2 feet above the seasonal high water table Overflow path or structure provided

At least 2 feet above the seasonal high water table Overflow path or structure provided General Conditions Map of proposed subwatershed to each subbasin, including total area and CN Design Flow or Design Volume to each STF, as appropriate Operation and Maintenance instructions for each STF