From: Revisiting Design Criteria for Stormwater Treatment Systems, Part 3

Table One

Table 1. Comparison of Design Criteria for Flow-Through Swales and Strips
Design Parameter	Washington	California	Texas	Virginia	Georgia	Denver
Performance Goal	80% TSSb			Based on TPc	80% TSSa
Volume Goal (%)	91	80			85	80d
SWALES
Manning's n	0.20 to 0.30	0.25	0.20	0.15	0.15	0.05
Residence time at design flow (min)	9e	10			5
Water depth at design flow (in)	2 if mowed, 4 if not	4	6		4	24
Grass height (in)		6			4
Min. longitudinal slope (%)	1.5			0.75		0.2
Max. longitudinal slope (%)	2.5	2.5	5	5		1
Max. velocity (fps)	1		1	1.5		1.5
Min. length (ft)	100	100
Max. width (ft)	10	10			6
STRIPS
Manning's n	0.35		0.20		0.15 to 0.35
Max. width of paved area treated (ft)	150	60			150	0.05 cfs/lin. ft
Max. longitudinal slope (%)	5	15	5	2	6	4
Max. water depth (in)	1		6			1
Detention time at peak flow (min)	9e				5
Minimum length (ft)		15	10	25	15
a. Goal is for other BMPs: does not consider swales and strips capable of achieving the goal. b. An effluent concentration of 20 mg/L at influent concentration less than 100 mg/L c. No specific goal is established. Removal expectations are provided for each type of system, ranging from 10% to 65%. d. The volume of 80% of the events is fully treated. e. If placed above a flood control detention facility or if such a facility is not required.