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MAXIMUM RAINFALL INTENSITY IN SOUTH CAROLINA BY COUNTY

John C. Purvis
Wes Tyler
Scott Sidlow

Climate Report No. G32 South Carolina State Climatology Office
2221 Devine Street
Suite 222
Columbia, South Carolina 29205-2418
June 1988

TABLE OF CONTENTS

Introduction
Maximum Rainfall Intensity Expected At the Center of Each County
References

INTRODUCTION

The growing environmental awareness of the past few years has increased the demand for hydrologic planning and design for small drainage areas. Examples of such drainage areas are cattle feedlots and urban shopping and parking areas. Hydrologic design practices and legal standards are generally expresses in terms of control of storm slow of a specified frequency of recurrence. Precipitation frequencies for short duration are an essential input to evaluating the runoff frequencies from small drainage areas.

Until about 1953, economic and engineering design requiring rainfall frequency data was based largely of Yarnell's paper which contains a series of generalized maps for several combinations of durations and return periods. Yarnell's maps are based on data from about 200 first order Weather Bureau stations which maintained complete recording-gauge records. In 1940, about 5 years after Yarnell's paper was published, a hydrologic network of recording gages was installed to supplement both the Weather Bureau recording gages and the relatively latger number of nonrecording gages. The additional recording pages have subsequently increased the amount of short-duration data by a factor or 20.

Weather Bureau Technical Paper No.24, Parts I and II, prepared for the Corps of Engineers in connection with their military construction program, contained the first studies covering an extended area which exploited the hydrologic network data. The results of this work showed the importance of the additional data in defining the short-duration rainfall frequency regime in the mountainous regions of the West. In many instances, the differences between Technical Paper No. 24 and Yarnell reach a factor of three, with the former generally being larger. Relationships developed and knowledge gained from these studies in the United States were then used to prepare similar reports for the costal regions of North Africa and several Arctic regions where recording gage data were lacking.

Cooperation between the Weather Bureau and the Soil Conservation Service began in 1955 for the purpose of defining the depth-area-duration-frequency regime in the United States. Technical Paper No. 25, which was partly a by-product of previous work performed for the Corps of Engineers, was the first paper published under the sponsorship of the Soil Conservation Service. This paper contains a series of rainfall intensity-duration-frequency curves for 200 first order Weather Bureau stations. Th is was followed by Technical Paper No. 28, which is an expansion of Technical Paper No. 24 to longer return periods and durations. Next t be published were the five parts of the Technical Paper No.29 series, which cover the region east of 90'W, Included in this series are seasonal variation on a frequency basis and area-depth curves so that the point frequency values can be transformed to real frequency.

In May, 1961, the Weather Bureau published a new study of rainfall frequency. This study entitled a A Weather Bureau Technical Paper No. 40 (Hershfield 1961)@, abbreviated TP-40, has been the standard for precipitation -frequency values for durations from 5 minutes to 24 hours over the Eastern United States for durations of less than 1 hour, the TP-40 values are derived by using nationwide, return-period independent ratios of shorter duration values to 1-hour values. While these average ratios are valid in many specific sections of the country, they have and observed, describable geographic pattern. It has also been found that the ratios vary with return period.

In 1977, Fredrick, Meyers and Auciellco completed a new study, NWS HYDRO-35, entitled A Five to 60-min Precipitation Frequency for the Eastern and Central United States. That publication analyzes the above variation and derives new 5- to 60-min precipitation frequencies for the 37 states, North Dakota to Texas and eastward. There were presented in the form of maps for 5-, 15-, and 60 min duration at the 2- and 100 year return periods, together with equations and nomograms for intraduration an intrareturn period interpolations.

Maximum Rainfall Intensity Expected at the Center of Each South Carolina County

Abbeville
Return
Period	5 min.	10 min	15 min	30 min	60 min	6 hr	12 hr	24 hr
2 yr	0.473		0.98	1.37	1.77	2.91	3.35	3.8
5 yr				1.69	2.14	3.49	4.1	4.75
10 yr				1.92	2.4	4	4.8	5.6
25 yr				2.18	2.78	4.8	5.7	6.55
50 yr				2.4	3.09	5.2	6.25	7
100 yr	0.838		1.77	2.69	3.87	5.7	6.9	7.8
Aiken
Return
Period	5 min.	10 min	15 min	30 min	60 min	6 hr	12 hr	24 hr
2 yr	0.492		1.05	1.42	1.91	2.92	3.3	3.8
5 yr				1.78	2.26	3.62	4.25	4.9
10 yr				2.05	2.55	4.2	4.85	5.6
25 yr				2.3	2.93	4.9	5.75	6.5
50 yr				2.54	3.21	5.4	6.25	7.25
100 yr	0.834		1.81	2.83	3.98	5.8	6.9	7.9
Allendale
Return
Period	5 min.	10 min	15 min	30 min	60 min	6 hr	12 hr	24 hr
2 yr	0.503		1.09	1.52	2.03	2.96	3.4	3.95
5 yr				1.9	2.36	3.84	4.45	5.25
10 yr				2.15	2.69	4.4	5.2	6
25 yr				2.41	3.06	5	6.1	6.9
50 yr				2.65	3.42	5.75	6.7	7.75
100 yr	0.819		1.84	2.94	4.13	6.1	7.5	8.65
Anderson
Return
Period	5 min.	10 min	15 min	30 min	60 min	6 hr	12 hr	24 hr
2 yr	0.468		0.97	1.33	1.76	2.93	3.4	4
5 yr				1.66	2.1	3.61	4.35	5
10 yr				1.88	2.37	4.25	4.85	5.75
25 yr				2.15	2.75	4.9	5.8	6.75
50 yr				2.37	3.04	5.5	6.5	7.4
100 yr	0.831		1.78	2.65	3.9	5.9	7	8
Bamberg
Return
Period	5 min.	10 min	15 min	30 min	60 min	6 hr	12 hr	24 hr
2 yr	0.499		1.09	1.5	2.01	2.95	3.35	3.95
5 yr				1.87	2.34	3.78	4.4	5.25
10 yr				2.15	2.67	4.4	5.2	6
25 yr				2.4	3.07	5	6.05	6.85
50 yr				2.64	3.43	5.7	6.7	7.7
100 yr	0.817		1.84	2.93	4.11	6.1	7.4	8.5
Barnwell
Return
Period	5 min.	10 min	15 min	30 min	60 min	6 hr	12 hr	24 hr
2 yr	0.498		1.07	1.49	1.98	2.94	3.35	3.9
5 yr				1.85	2.32	3.74	4.35	5.1
10 yr				2.1	2.61	4.3	5	5.8
25 yr				2.36	2.99	4.95	5.9	6.75
50 yr				2.58	3.33	5.6	6.5	7.5
100 yr	0.824		1.83	2.9	4.06	5.9	7.25	8.25
Beaufort
Return
Period	5 min.	10 min	15 min	30 min	60 min	6 hr	12 hr	24 hr
2 yr	0.52		1.15	1.66	2.28	3.24	3.9	4.6
5 yr				2.04	2.6	4.25	5.1	5.9
10 yr				2.32	2.89	4.9	6	6.9
25 yr				2.64	3.36	5.6	6.8	7.95
50 yr				2.95	3.74	6.25	7.4	8.9
100 yr	0.796		1.9	3.12	4.35	7	8.4	10
Berkeley
Return
Period	5 min.	10 min	15 min	30 min	60 min	6 hr	12 hr	24 hr
2 yr	0.5		1.12	1.62	2.19	3.08	3.6	4.25
5 yr				1.98	2.5	4.08	4.8	5.6
10 yr				2.25	2.85	4.7	5.6	6.6
25 yr				2.58	3.26	5.3	6.5	7.5
50 yr				2.89	3.65	6.15	7.15	8.4
100 yr	0.8		1.85	3.12	4.23	6.75	8.2	9.5
Calhoun
Return
Period	5 min.	10 min	15 min	30 min	60 min	6 hr	12 hr	24 hr
2 yr	0.49		1.06	1.46	1.96	2.9	3.25	3.85
5 yr				1.81	2.3	3.66	4.3	5.05
10 yr				2.1	2.64	4.3	5	5.8
25 yr				2.35	3.04	4.95	5.85	6.7
50 yr				2.6	3.36	5.5	6.5	7.5
100 yr	0.821		1.82	2.92	4.06	6	7.25	8.3
Charleston
Return
Period	5 min.	10 min	15 min	30 min	60 min	6 hr	12 hr	24 hr
2 yr	0.511		1.15	1.65	2.27	3.25	4	4.6
5 yr				2.05	2.62	4.2	5.1	5.9
10 yr				2.35	2.92	4.8	5.9	7
25 yr				2.65	3.35	5.6	6.75	8
50 yr				2.95	3.73	6.4	7.45	8.9
100 yr	0.795		1.88	3.14	4.34	7	8.5	10.2
Cherokee
Return
Period	5 min.	10 min	15 min	30 min	60 min	6 hr	12 hr	24 hr
2 yr	0.464		0.96	1.27	1.76	2.6	3	3.4
5 yr				1.59	2.01	3.4	3.95	4.5
10 yr				1.82	2.31	3.9	4.45	5
25 yr				2.14	2.71	4.9	5	5.85
50 yr				2.34	3.01	5	5.75	6.75
100 yr	0.821		1.76	2.65	3.91	5.75	6.5	7.2
Chester
Return
Period	5 min.	10 min	15 min	30 min	60 min	6 hr	12 hr	24 hr
2 yr	0.475		0.99	1.3	1.76	2.68	3	3.35
5 yr				1.65	2.1	3.32	3.95	4.35
10 yr				1.9	2.38	3.8	4.5	5.15
25 yr				2.19	2.78	4.75	5.1	5.9
50 yr				2.42	3.11	4.9	5.6	6.8
100 yr	0.84		1.76	2.75	3.78	5.55	6.4	7.3
Chesterfield
Return
Period	5 min.	10 min	15 min	30 min	60 min	6 hr	12 hr	24 hr
2 yr	0.483		1.03	1.42	1.85	2.75	3.25	3.7
5 yr				1.75	2.24	3.46	4.2	4.75
10 yr				2.05	2.59	4	4.8	5.55
25 yr				2.32	2.96	4.85	5.5	6.4
50 yr				2.56	3.26	5.2	6.25	7.25
100 yr	0.835		1.8	2.88	3.85	5.8	6.85	7.95
Clarendon
Return
Period	5 min.	10 min	15 min	30 min	60 min	6 hr	12 hr	24 hr
2 yr	0.493		1.08	1.5	2.02	2.92	3.35	3.9
5 yr				1.87	2.36	3.77	4.4	5.25
10 yr				2.19	2.73	4.4	5.25	6
25 yr				2.45	3.13	5	6	6.85
50 yr				2.71	3.48	5.7	6.75	7.8
100 yr	0.812		1.83	3	4.12	6.25	7.5	8.75
Colleton
Return
Period	5 min.	10 min	15 min	30 min	60 min	6 hr	12 hr	24 hr
2 yr	0.51		1.12	1.6	2.18	3	3.5	4.25
5 yr				1.99	2.46	4.02	4.75	5.6
10 yr				2.25	2.8	4.6	5.55	6.5
25 yr				2.55	3.25	5.3	6.55	7.5
50 yr				2.8	3.59	6	7.1	8.3
100 yr	0.8		1.86	3.06	4.25	6.6	8	9.4
Darlington
Return
Period	5 min.	10 min	15 min	30 min	60 min	6 hr	12 hr	24 hr
2 yr	0.487		1.05	1.45	1.94	2.82	3.3	3.8
5 yr				1.81	2.29	3.59	4.3	5
10 yr				2.11	2.66	4.2	5	5.7
25 yr				2.37	3.05	4.9	5.65	6.6
50 yr				2.64	3.36	5.4	6.4	7.45
100 yr	0.825		1.82	2.95	4.01	6	7.2	8.3
Dillon
Return
Period	5 min.	10 min	15 min	30 min	60 min	6 hr	12 hr	24 hr
2 yr	0.488		1.06	1.49	1.97	2.87	3.35	3.9
5 yr				1.86	2.35	3.73	4.35	5.1
10 yr				2.17	2.74	4.35	5.2	5.9
25 yr				2.46	3.15	4.95	5.8	6.8
50 yr				2.74	3.5	5.55	6.6	7.7
100 yr	0.818		1.82	3.04	4.06	6.25	7.45	8.55
Dorchester
Return
Period	5 min.	10 min	15 min	30 min	60 min	6 hr	12 hr	24 hr
2 yr	0.501		1.12	1.6	2.15	2.99	3.5	4.25
5 yr				1.95	2.47	4.01	4.75	5.5
10 yr				2.25	2.8	4.7	5.5	6.5
25 yr				2.53	3.24	5.3	6.5	7.4
50 yr				2.81	3.6	6	7.1	8.2
100 yr	0.801		1.85	3.06	4.24	6.6	8	9.4
Edgefield
Return
Period	5 min.	10 min	15 min	30 min	60 min	6 hr	12 hr	24 hr
2 yr	0.485		1.03	1.39	1.86	2.91	3.25	3.8
5 yr				1.74	2.21	3.53	4.2	4.75
10 yr				1.99	2.47	4.05	4.75	5.5
25 yr				2.26	2.86	4.8	5.7	6.45
50 yr				2.48	3.16	5.25	6.05	7.1
100 yr	0.841		1.79	2.78	3.96	5.6	6.8	7.8
Fairfield
Return
Period	5 min.	10 min	15 min	30 min	60 min	6 hr	12 hr	24 hr
2 yr	0.481		1.02	1.34	1.83	2.78	3.1	3.55
5 yr				1.69	2.16	3.39	4	4.5
10 yr				1.96	2.42	3.9	4.6	5.25
25 yr				2.24	2.84	4.8	5.25	6.1
50 yr				2.46	3.15	4.95	5.85	6.9
100 yr	0.84		1.78	2.79	3.86	5.6	6.6	7.5
Florence
Return
Period	5 min.	10 min	15 min	30 min	60 min	6 hr	12 hr	24 hr
2 yr	0.49		1.07	1.5	2	2.91	3.35	3.9
5 yr				1.86	2.37	3.83	4.4	5.25
10 yr				2.2	2.76	4.35	5.2	6
25 yr				2.46	3.14	5	5.9	6.85
50 yr				2.75	3.51	5.7	6.7	7.75
100 yr	0.812		1.83	3.05	4.09	6.25	7.6	8.7
Georgetown
Return
Period	5 min.	10 min	15 min	30 min	60 min	6 hr	12 hr	24 hr
2 yr	0.499		1.12	1.6	2.17	3.13	3.75	4.5
5 yr				2	2.54	4.12	5	5.7
10 yr				2.34	2.9	4.7	5.7	6.75
25 yr				2.6	3.3	5.4	6.5	7.75
50 yr			1.55	2.95	3.69	6.15	7.2	8.6
100 yr	0.798		1.85	3.13	4.24	6.8	8.25	9.75
Greenville
Return
Period	5 min.	10 min	15 min	30 min	60 min	6 hr	12 hr	24 hr
2 yr	0.462		0.95	1.29	1.78	2.93	4.1	4.6
5 yr				1.62	2.04	3.89	4.4	5.25
10 yr				1.84	2.33	4.3	5	5.8
25 yr				2.13	2.7	4.9	5.7	6.75
50 yr				2.33	2.99	5.6	6.6	7.6
100 yr	0.825		1.79	2.62	3.98	5.9	7	8.3
Greenwood
Return
Period	5 min.	10 min	15 min	30 min	60 min	6 hr	12 hr	24 hr
2 yr	0.475		0.99	1.36	1.78	2.89	3.25	3.75
5 yr				1.7	2.15	3.46	4.1	4.7
10 yr				1.94	2.39	3.95	4.7	5.45
25 yr				2.2	2.79	4.75	5.55	6.35
50 yr				2.42	3.11	5.1	5.9	6.95
100 yr	0.841		1.78	2.72	3.94	5.6	6.75	7.7
Hampton
Return
Period	5 min.	10 min	15 min	30 min	60 min	6 hr	12 hr	24 hr
2 yr	0.51		1.11	1.57	2.12	2.98	3.4	4.1
5 yr				1.93	3.39	3.9	4.5	5.4
10 yr				2.2	2.74	4.5	5.3	6.4
25 yr				2.49	3.14	5.2	6.35	7.2
50 yr				2.71	2.51	5.85	6.9	7.9
100 yr	0.81		1.86	3	4.2	6.4	7.75	8.9
Horry
Return
Period	5 min.	10 min	15 min	30 min	60 min	6 hr	12 hr	24 hr
2 yr	0.496		1.1	1.56	2.11	3.11	3.5	4.25
5 yr				1.95	2.48	4.03	4.75	5.5
10 yr				2.3	2.88	4.65	5.45	6.55
25 yr				2.58	3.29	5.3	6.3	7.6
50 yr				2.91	3.67	5.95	7	8.35
100 yr	0.801		1.84	3.13	4.18	6.75	8	9.6
Jasper
Return
Period	5 min.	10 min	15 min	30 min	60 min	6 hr	12 hr	24 hr
2 yr	0.513		1.13	1.61	2.21	3.09	3.65	4.35
5 yr				1.99	2.5	4	4.75	5.65
10 yr				2.26	2.8	4.75	5.6	6.6
25 yr				0.255	3.24	5.45	6.6	7.6
50 yr				2.82	3.59	6	7.2	8.3
100 yr	0.8		1.87	3.07	4.27	6.75	8.1	9.5
Kershaw
Return
Period	5 min.	10 min	15 min	30 min	60 min	6 hr	12 hr	24 hr
2 yr	0.483		1.03	1.4	1.86	2.77	3.15	3.65
5 yr				1.74	2.23	3.45	4.15	4.7
10 yr				2.04	2.54	4	4.75	5.5
25 yr				2.3	2.94	4.85	5.4	6.35
50 yr				2.54	3.24	5.1	6.2	7.2
100 yr	0.837		1.8	2.85	3.88	5.75	6.8