FLOOD MAGNITUDE AND FREQUENCY OF LITTLE 

MANTUA CREEK AT THE CULVERT AT MILEPOST 7.8 

ON NEW JERSEY ROUTE 44, AND AT THE CONRAIL 

CULVERT 0.20 MILES DOWNSTREAM, WEST 

DEPTFORD TOWNSHIP, GLOUCESTER COUNTY, 

NEW JERSEY 

U.S. GEOLOGICAL SURVEY 

Open-File Report 96-326 

Prepared in cooperation with the 

NEW JERSEY DEPARTMENT OF TRANSPORTATION 
FLOOD MAGNITUDE AND FREQUENCY OF LITTLE 

MANTUA CREEK AT THE CULVERT AT MILEPOST 7.8 

OF NEW JERSEY ROUTE 44, AND AT THE CO~RAIL 

CULVERT 0.20 MILES DOWNSTREAM, WEST 

DEPTFORD TOWNSHIP, GLOUCESTER COUNTY, 

NEW JERSEY 

By T,'1omas Barringer 

u.s. GEOLOGICAL SURVEY 

Open-File Report 96-326 

Prepared in cooperation with the 

NEW JERSEY DEPARTMENT OF TRANSPORTATION 

West Trenton, New Jersey 

1996 
u.s. DEPARTMENT OF THE INTERIOR 

BRUCE BABSln, Secretary 

U.s. GEOLOGICAL SURVEY 

Gordon p, Eaton I Director 

For additional infonnation Copies of this report can be 

write to: obtained from: 

District Chief U.S Geological Survey 

U.S Geological Survey Earth Science Infonnation Center 

Mountain View Office Park Open-File Reports Section 

810 Bear Tavern Road, Suite 206 Box 25286, MS 517 

West Trenton, NJ 08628 Denver Federal Center 

Denver, CO 80225 
CONTENTS 

Page 

Abstract .................................................................................................................................... : ..................... 1 

Introduction .................................................................................................................................................... 1 

Methods for determining flood magnitude and frequency ............................................................................ 1 

New Jersey Department of Environmental Protection Special Report 38 Method ................................... 0 ••• 3 

Results .......................................................................................................................................................... :.3 

Selected references .................................................................................................................................. 0 ••••• 8 

ILLUSTRATIONS 

Figure 1. Map showing location of Little Mantua Creek at the culvert at milepost 7.8 on New Jersey 

Route 44, and at the Conrail culvert 0.20 miles downstream, and associated drainage 

basin, West Deptford Township, New Jersey ................................................................ 0. 2 

TABLES 

Table 1. Explanatory variables for the flood-magnitude and -frequency analysis of Little Mantua Creek 

at the culvert on New Jersey Route 44, milepost 7.8, West Deptford Township, 

Gloucester County, New Jersey ................................................................................ ~ .......... 4 

2. Explanatory variables for the flood-magnitude and -frequency analysis of Little Mantua Creek 

at the Conrail culvert downstream from the culvert on New Jersey Route 44, milepost 7.8, 

West Deptford Township, Gloucester County, New Jersey ................................................. 5 

3. Estimates of flood magnitudes for selected flood frequencies, Little Mantua Creek at the 

culvert on New Jersey Route 44, milepost 7.8, West Deptford Township, Gloucester 

County, New Jersey ........................................................................................................... 0.6 

4. Estimates of flood magnitudes for selected flood frequencies, Little Mantua Creek at the 

Conrail culvert downstream from the culvert on New Jersey Route 44, milepost 7.8, 

West Deptford Township, Gloucester County, New Jersey ................................................. 7 

iii 
CONVERSION FACTORS 

Multiply To obtain 

foot (ft) 0.3048 meter 

mile (mi) 1.609 kilometer 

square mile (mi2) 2.590 square kilometer 

foot per mile (ftlmi) 0.189 meter per kilometer 

cubic foot per second (ft3/s) 0.0283 cubic meter per second 

lV 
FLOOD MAGNITUDE AND FREQUENCY OF LITTLE MANTUA CREEK 

AT THE CULVERT AT MILEPOST 7.8 OF NEW JERSEY ROUTE 44, 

AND AT THE CONRAIL CULVERT 0.20 MILES DOWNSTREAM, 

WEST DEPTFORD TOWNSHIP, GLOUCESTER COUNTY, NEW JERSEY 

By Thomas Barringer 

ABSTRACT 

The magnitude and frequency of floods at Little Mantua Creek at the culvert on New Jersey Route 

44 at milepost 7.8 and at the Conrail culvert 0.20 miles downstream, in West Deptford Township, New 

Jersey; were determined by using the New Jersey Department of Environ..mental Protection Special Report 

38 method. Flood-magnitude and -frequency estimates, as well as drainage-basin characteristics, are 

included in this report. The l00-year-flood estimates are 249 cubic feet per second at the culvert on New 

Jersey Route 44, and 243 cubic feet per second at the Conrail culvert. 

INTRODUCTION 

Information on the magnitude and frequency of floods is critical to the planning and design of 

highway culverts and bridges. Such information is not readily available for many stream crossings in New 

Jersey. To fulfill this information need, the U.S. Geological Survey (USGS), in cooperation with the New 

Jersey Department of Transportation, began an analysis of flood data from stream-crossing sites on New 

Jersey streams. 

This report presents results of the analysis for Little Mantua Creek at the culvert on New Jersey 

Route 44 at milepost 7.8 (Crown Point Road) and at the Conrail culvert 0.20 miles downstream, in West 

Deptford Township, New Jersey (fig. 1). The drainage area upstream from the Route 44 site is 1.48 mi2

, 2 and the drainage area upstream from the Conrail site is 1.58 mi . A field reconnaissance was performed on 

March 21, 1995, to verify the locations of drainage-basin divides and basin characteristics. Both sites analyzed in this report occasionally are affected by tidal flows. The presence of the Conrail culvert lessens 

tidal effects at the Route 44 site. These tidal effects were not considered in the calculations of flood magnitude and frequency. 

The flood-insurance study for West Deptford Township (Federal Emergency Management Agency, 

1981) does not include a detailed study of Little Mantua Creek; therefore, flood discharges were not determined previously. 

METHODS FOR DETERMINING FLOOD MAGNITUDE AND FREQUENCY 

Various methods for calculating flood magnitude and frequency were considered for use in determining the flood magnitudes that are likely to be exceeded at these sites within a given number of years 

(recurrence interval). The rational method (Chow arid others, 1988), New Jersey Department of Environmental Protection (NJDEP) Special Report 38 method (SR38) (Stankowski, 1974), the U.S. Soil Conservation Service (SCS) Technical Release 55 (TR-55) method (U.S. Soil Conservation Service, 1986), a 

variation of the USGS transfer method (New Jersey Department of Environmental Protection, 1993), and 

the USGS index-flood method (Thomas, 1964) were all considered for use in determining the flood magnitude and frequency of Little Mantua Creek at the subject sites in West Deptford Township, New Jersey. 

1 
Base from U.S. Geological Survey 1 :24,000, quadrangle, 

Woodbury, 1967, photorevised 1986 

o 1 MILE 75° 

I I I 

o 1 KILOMETER 

EXPLANATION 

_ ................. DRAINAGE-BASIN BOUNDARY 

-_ .. _- SUBBASIN BOUNDARY 

o CULVERT SITE 

Figure 1. Location of Little Mantua Creek at the culvert at milepost 7.8 on New Jersey 

Route 44, and at the Conrail culvert 0.20 miles downstream, and associated drainage 

basin, West Deptford Township, New Jersey. 

2 
NEW JERSEY DEPARTMENT OF'ENVIRONMENTAL PROTECTION 

SPECIAL REPORT 38 METHOD 

The New Jersey Department of Environmental Protection Special Report 38 method (Stankowski, 

1974) was chosen to estimate peak streamflows at the subject sites. This method can be used for drainage 2 

areas of more than I mi but less than 1,000 mi2

; therefore, it is suitable for use at the subject sites. The 

method is based on a set of drainage-basin characteristics that are used as predictors in a set of regression 

equations. Each equation in the set corresponds to a different recurrence interval. The characteristics 

include drainage-basin area, main-channel slope, surface storage, and impervious-surface area. 

Estimates made with this method were compared with estimates made with several other method~. 

Estimates made with the USGS transfer method required the use offlood data from streamflow-gaging stations located in basins that have drainage area" and other basin characteristics similar to those at the subject sites. Peak-flow estimates also were made by using the rational and TR-55 methods. 

The estimate of the 1 DO-year flood made for the Route 44 site by using the USGS transfer method 

with data from station 01467305 (Newton Creek at Collingswood, New Jersey) was 1.4 times that made by 

using the SR38 method. Similarly, the estimate for the Conrail site made by using the USGS transfer 

method with data from station 01467305 was 1.5 times that made by using the SR38 method. The estimates obtained by using the rational and TR-55 methods appear to be high and seem inappropriate for 

these sites. The estimates made by using the SR38 method agreed closely with the estimates made by 

using the USGS transfer method; therefore the SR38 estimates were chosen for this analysis. 

RESULTS 

Flood data from nearby streamflow- or crest-stage gaging stations provide a good indication of the 

flood magnitude and frequency that can be expected at an ungaged site, particularly when drainage area 

and other basin characteristics are similar. In this study, estimates were obtained by using the NJDEP SR38 

method and compared with estimates made by using the USGS transfer method. Flood data collected at 

three nearby streamflow-gaging stations (Newton Creek at Collingswood, New Jersey, 01467305; South 

Branch Newton Creek at Haddon Heights, New Jersey, 01467317; and West Branch Cohansey River at 

Seeley, New Jersey, 01412500) were used in applying the transfer method. These three stations were chosen from among other nearby stations because their drainage-basin characteristics are most similar to those 

at the culvert sites. Tidal effects at the two culvert sites were not considered. 

The explanatory variables used in applying the USGS transfer method for the culvert sites are 

listed in tables 1 and 2. The flood-magnitude and -frequency estimates for the subject sites are shown in 

tables 3 and 4. The estinlate of the 100-year flood discharge at the culvert at the New Jersey Route 44 is 

249 tt3 Is; that for the Conrail culvert site is 243 ffls. 

3 
Table 1. Explanatory variables for the flood-magnitUde and -frequency analysis of Little Mantua Creek at 

the culvert on New Jersey Route 44, milepost 7.8, West Deptford Township, Gloucester County, 

New Jersey 

Drainage area: 1.48 square miles 

Latitude: 39°50'24" 

Longitude: 75°12'43" 

Highway: New Jersey Route 44 

Milepost: 7.8 

U.S. Geological Survey 7-1/2-minute quadrangle: Woodbury, N.J.-Pa. 

Variable Value Unit 

Drainage area 

Main-channel slope 

Surface-storage index 

Total stream length 

Population density (1990) 

Impervious cover 

Lake and swamp area 

= 

= 

= 

= 

= 

= 

= 

1.48 

27.9 

6.4 

2.44 

1,076 

13 

5.4 

square miles 

feet per mile 

percent 

mile 

persons per square mile 

percent 

percent 

4 
Table 2. Explanatory variables for the flood-magnitu'de and -frequency analysis of Little Mantua Creek at 

the Conrail culvert downstream from the culvert on New Jersey Route 44, milepost 7.8, West Deptford 

Township, Gloucester County, New Jersey 

Drainage area: 1.58 square miles 

Latitude: 39° 50'23'~ 

Longitude: 75° 12' 42" 

Site: Conrail culvert downstream from the culvert on New Jersey Route 44 

Milepost: 7.8 

U.S. Geological Survey 7-112-minutc quadrangle: Woodbury, N.J.-Pa. 

Variable Value Unit 

Drainage area = 1.58 square miles 

Main-channel slope = 26.6 feet per mile 

Surface-storage index = 7.3 percent 

Total stream length = 2.71 miles 

Population density (199O) = 1,076 persons per square mile 

Impervious cover = 13 percent 

Lake and swamp area = 6.3 percent 

5 
Table 3. Estimates of flood magnitudes for selected ffood frequencies, Little Mantua Creek at the culvert 

on New Jersey Route 44, milepost 7.8, West Deptford Township, Gloucester County, New Jersey 

[Q, flood-magnitude estimates in cubic feet per second along with number indicating frequency of the 

recurrence inteIVal in years; NJDEP SR, New Jersey Department of Environmental Protection Special 

Report] 

Drainage area: 1.48 square miles 

Latitude: 39° 50' 24" 

Longitude: 75° 12' 43" 

Highway: New Jersey Route 44 

Milepost: 7.8 

U.S. Geological SUIVey 7-1/2-minute quadrangle: Woodbury, N.J.-Pa. 

Estimating method Q2 Q5 QI0 Q25 Q50 QIOO 

NJDEP SR 38 55 85 116 162 201 249 

6 
Table 4.--Estimates of flood magnitudes for selected 'flood frequencies, Little Mantua Creek at the Conrail 

culvert downstream from the culvert on New Jersey Route 44, milepost 7.8, West Deptford Township, 

Gloucester County, New Jersey 

[Q, flood-magnitude estimates in cubic feet per second along with number indicating frequency of the 

recurrence interval in years; NJDEP SR, New Jersey Department of Environmental Protection Special 

Report] 

Drainage area: 1.58 square miles 

Latitude: 39° 50'23" 

Longitude: 75° 12' 42" 

Site: Conrail culvert downstream from the culvert on New Jersey Route 44 

Milepost: 7.8 

U.S. Geological Survey 7-1/2-minute quadrangle: Woodbury, N.J.-Pa. 

Estimating method Q2 Q5 QI0 Q25 Q50 QI00 

NJDEPSR 38 54 83 113 158 196 243 

7 
SELECTED REFERENCES 

Chow, V.T.. Maidment, D.R., and Mays, L.W., 1988, Applied hydrology: New York, McGraw-Hill, 572 p. 

Federal Emergency Management Agency, 1981, Flood insurance study, Township of West Deptford, New 

Jersey: Federal Emergency Management Agency, December 1981, 18 p., 13 pIs. 

New Jersey Department of Environmental Protection, 1993, Technical manual for stream encroachment 

permits: New Jersey Department of Environmental Protection and Energy, Land Use Regulation 

Program, Bureau of Inland Regulation, Bureau of Coastal Regulation, May 1993, 100 p., 6 app. 

Stankowski, SJ., 1974, Magnitude and frequency offloods in New Jersey with effects of urbanization: 

New Jersey Department of Environmental Protection, Special Report 38,46 p. 

Thomas, D.M., 1964, Floods in New Jersey, magnitude and frequency: New Jersey Department of 

Conservation and Economic Development, Water Resources Circular 13, 145 p. 

U.S. Soil Conservation Service, 1986, Urban hydrology for small watersheds: Engineering Division 

Technical Release 55, Washington, D.C., 162 p. 

8