Sec. 9-403 Allowable Release Rate.

   a.   The allowable release rate of storm water originating from a proposed development shall not exceed the amount specified herein under Storm Water Control Policy, and as described herein.

   b.   In the event the natural downstream channel or storm sewer system is inadequate to accommodate the release rate provided above, then the allowable release rate shall be reduced to that rate permitted by the capacity of the receiving downstream channel or storm sewer system and additional detention as determined by the Town Engineer or its designee after review and recommendation of the Plan Commission shall be required to store that portion of the runoff exceeding the capacity of the receiving sewers or waterways.

   c.   If more than one (1) detention basin is involved in the development of the area upstream of the limiting restriction, the allowable release rate from any one (1) detention basin shall be in direct proportion to the ratio of its drainage area to the drainage area of the entire watershed upstream of the restriction.

Table 5
Rainfall Depths for Various Return Periods and Storm Durations
Depth (Inches)
Duration	Return Period (Years)
	2	5	10	25	50	100
5 min	0.42	0.52	0.59	0.68	0.75	0.82
10 min.	0.64	0.79	.91	1.04	1.15	1.25
15 min.	0.80	0.99	1.13	1.29	1.43	1.55

 

Table 5
Rainfall Depths for Various Return Periods and Storm Durations
Depth (Inches)
Duration	Return Period (Years)
	2	5	10	25	50	100
20 min.	0.95	1.17	1.34	1.53	1.70	1.85
30 min.	1.11	1.37	1.57	1.79	1.98	2.16
40 min.	1.23	1.52	1.74	1.99	2.20	2.40
50 min	1.33	1.64	1.87	2.14	2.36	2.58
60 min.	1.40	1.73	1.97	2.26	2.49	2.72
1.5 hrs.	1.70	2.09	2.39	2.73	3.03	3.30
2 hrs.	1.71	2.11	2.41	2.76	3.05	3.33
3 hrs.	1.84	2.27	2.60	2.97	3.29	3.59
4 hrs.	2.06	2.54	2.90	3.31	3.67	4.00
5 hrs.	2.16	2.66	3.04	3.48	3.85	4.20
6 hrs.	2.22	2.74	3.13	3.58	3.96	4.32
7 hrs.	2.31	2.85	3.26	3.72	4.12	4.49
8 hrs.	2.35	2.90	3.32	3.79	4.20	4.58
9 hrs.	2.42	2.99	3.41	3.90	4.32	4.71
10 hrs.	2.49	3.07	3.51	4.01	4.44	4.84
12 hrs.	2.58	3.18	3.63	4.15	4.59	5.01
14 hrs.	2.66	3.29	3.76	4.30	4.75	5.18
16 hrs.	2.75	3.40	3.88	4.44	4.91	5.39
18 hrs.	2.82	3.48	3.98	4.55	5.03	5.49
20 hrs.	2.89	3.56	4.07	4.65	5.15	5.62
24 hrs.	3.00	3.70	4.23	4.83	5.35	5.83

 

Table 5A
Rainfall Intensities for Various Return Periods and Storm Durations
Intensity (Inches/Hour)
Duration	Return Period (Years)
	2	5	10	25	50	100
5 min	5.04	6.24	7.08	8.16	9.00	9.84
10 min.	3.84	4.74	5.46	6.24	6.90	7.50
15 min.	3.20	3.96	4.52	5.16	5.72	6.20
20 min.	2.85	3.51	4.02	4.59	5.10	5.55
30 min.	2.22	2.74	3.12	3.58	3.96	4.32
40 min.	1.85	2.28	2.61	2.99	3.30	3.60
50 min	1.60	1.97	2.24	2.57	2.83	3.10
60 min.	1.40	1.73	1.97	2.25	2.49	2.72
1.5 hrs.	1.13	1.39	1.59	1.82	2.02	2.20
2 hrs.	0.86	1.06	1.21	1.38	1.53	1.67
3 hrs.	0.61	0.76	0.87	0.99	1.10	1.20
4 hrs.	0.52	0.64	0.73	0.83	0.92	1.00
5 hrs.	0.43	0.53	0.61	0.70	0.77	0.84
6 hrs.	0.37	0.46	0.52	0.60	0.66	0.72
7 hrs.	0.33	0.41	0.47	0.53	0.59	0.64
8 hrs.	0.29	0.36	0.42	0.47	0.53	0.57
9 hrs.	0.27	0.33	0.38	0.43	0.48	0.52
10 hrs.	0.25	0.31	0.35	0.40	0.44	0.48
12 hrs.	0.22	0.27	0.30	0.35	0.38	0.42
14 hrs.	0.19	0.24	0.27	0.31	0.34	0.37

 

Table 5A
Rainfall Intensities for Various Return Periods and Storm Durations
Intensity (Inches/Hour)
Duration	Return Period (Years)
	2	5	10	25	50	100
16 hrs.	0.17	0.21	0.24	0.28	0.31	0.34
18 hrs.	0.16	0.19	0.22	0.25	0.28	0.31
20 hrs.	0.14	0.18	0.20	0.23	0.26	0.28
24 hrs.	0.13	0.15	0.18	0.20	0.22	0.24

 

(Ord. No. 1708, 6-13-07)