FLOOD MAGNITUDE AND FREQUENCY OF MAIN 

DITCH AT THE CULVERT ON NEW JERSEY ROUTE 44 

AND AT THE CONRAIL CULVERT DOWNSTREAM, 

WEST DEPTFORD TOWNSHIP, GLOUCESTER 

COUNTY, NEW JERSEY 

u.s. GEOLOGICAL SURVEY 

Open-File Report 96-325 

Prepared in cooperation with the 

NEW JERSEY DEPARTMENT OF TRANSPORTATION 
FLOOD MAGNITUDE AND 'FREQUENCY OF MAIN 

DITCH AT THE CULVERT ON NEW JERSEY ROUTE 44 

AND AT THE CONRAIL CULVERT DOWNSTREAM, 

WEST DEPTFORD TOWNSHIP, GLOUCESTER 

COUNTY, NEW JERSEY 

By Thomas Barringer 

u.s. GEOLOGICAL SURVEY 

Open-File Report 96-325 

Prepared in cooperation with the 

NEW JERSEY DEPARTMENT OF TRANSPORTATION 

West Trenton, New Jersey 

1996 
u.s. DEPARTMENT OF THE INTERIOR 

BRUCE BABBln, Secretary 

U.s. GEOLOGICAL SURVEY 

Gordon P. Eaton, 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. 0 .......................................... 0 .......... 0 .... 0 .......................................................................... 0 •••••••••••• 1 

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

New Jersey Department of Environmental Protection Special Report 38 method ........................................ 3 

Results ............................................................................................................................................................ 3 

Selected references ........................................................................................................................................ 8 

ILLUSTRATIONS 

Figure 1. Map showing location of Main Ditch at the culvert at milepost 8.3 on New Jersey Route 44 

and at the Conrail culvert 0.21 miles downstream and associated drainage basins, West 

Deptford Township, New Jersey ..................................................................................... 2 

TABLES 

Table 1. Explanatory variables for the flood-magnitude and -frequency analysis of Main Ditch at the 

culvert on New Jersey Route 44, West Deptford Township, New Jersey ........................... 4 

2. Explanatory variables for the flood-magnitude and -frequency analysis of Main Ditch at the 

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

Township, New Jersey ......................................................................................................... 5 

3. Estimates of flood magnitudes for selected flood frequencies, Main Ditch at the culvert on 

New Jersey Route 44, West Deptford Township, New Jersey ........................................... 6 

4. Estimates of flood magnitudes for selected flood frequencies, Main Ditch at the Conrail 

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

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 

IV 
FLOOD MAGNITUDE AND FREQUENCY OF MAIN DITCH AT THE 

CULVERT ON NEW JERSEY ROUTE 44 AND AT THE CONRAIL 

CULVERT DOWNSTREAM, WEST DEPTFORD TOWNSHIP, 

GLOUCESTER COUNTY, NEW JERSEY 

By Thomas Barringer 

ABSTRACT 

The magnitude and frequency of floods at Main Ditch at the culvert on New Jersey Route 44 at 

milepost 8.3 and at the Conrail culvert 0.21 miles downstream, in West Deptford Township, New Jersey, 

were detennined by using the New Jersey Department of Enviro!uuental Protection Special Report 38 

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

in this report. The 100-year-flood estimates are 285 cubic feet per second at the culvert on New Jersey 

Route 44 and 345 cubic feet per second at the Conrail culvert. 

INTRODUCTION 

Infonnation 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 infonnation 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 Main Ditch at the culvert on New Jersey Route 44 

(Crown Point Road) at milepost 8.3 and at the Conrail culvert 0.21 miles downstream, in West Deptford 

Township, New Jersey (fig. 1). The drainage area upstream from Route 44 site is 0.48 mi2, and the drainage area upstream from the Conrail culvert site is 0.55 mi2. A field reconnaissance was performed on 

February 23, 1995, to verify the locations of drainage-basin divides and basin characteristics. Both sites 

discussed in this report are subject to occasional tidal effects; these 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 this stream; therefore, flood discharges were not detennined 

previously. 

METHODS FOR DETERMINING FLOOD MAGNITUDE AND FREQUENCY 

Various widely used 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 and others, 1988), New Jersey Department of 

Environmental Protection (NJDEP) Special Report 38 method (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 detennining the flood magnitude and frequency of Main Ditch 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' 74' 

I 

I I 

o 1 KILOMETER 

EXPLANATION 

_ •• - DRAINAGE-BASIN BOUNDARY 

o CULVERT SITE 

Figure 1. Location of Main Ditch at the culvert at milepost 8.3 on New Jersey 

Route 44 and at the Conrail culvert 0.21 miles downstream and associated 

drainage basins, West Deptford Township, New Jersey. 

2 
NEW JERSEY DEPARTMENT OF ENVmONMENTAL PROTECTION SPECIAL 

REPORT 38 METHOD 

The New Jersey Department of Environmental Protection Special Report 38 method (SR 38) 

(Stankowski, 1974) was chosen to estimate peak streamflows at the subject sites. Estimates made with the 

SR 38 method are based on a set of regression equations in which the predictors are drainage-basin area, 

main-channel slope, surface storage, and amount of impervious cover. 

Estimates made with this method were compared with estimates made using several other methods. Estimates made with the USGS transfer method required the use of flood data from nearby streamflow-gaging stations located in basins that have drainage areas 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 estimates of the lOO-year flood made fbrthe Route 44 site by using the USGS transfer method 

with data from station 01467317 (South Branch of Newton Creek at Haddon Heights, New Jersey) were 

1.2 times that made by using the SR 38 method. Similarly, estimates for the Conrail site made with the 

USGS transfer method were 1.2 times that made by using the SR 38 method. The estimate made by using 

the SR 38 method agreed closely with the estimates made by using the USGS transfer method; therefore, 

the SR 38 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 

SR 38 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 USGS 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 SR 38 method at 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. 

3 The estimate of the 100-year flood discharge at the culvert at New Jersey Route 44 site is 285 ft /s; that for 

the Conrail culvert site is 345 ft3 Is. 

3 
Table 1. Explanatory variables for the flood-magnitude and -frequency analysis of Main Ditch at the 

culvert on New Jersey Route 44, West Deptford Township, New Jersey 

Drainage area: 0.48 square miles 

Latitude: 39° 50' 28" 

Longitude: 75° 12' 03" 

Highway: New Jersey Route 44 

Milepost: 8.3 

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

Variable Value Unit 

Drainage area :: 0.48 square miles 

Main-channel slope :: 46.7 feet per mile 

Surface-storage index :: 1.0 percent 

Total stream length :: 1.00 mile 

Population density (1990) :: 1,076 persons per square mile 

Impervious cover :: 13 percent 

Lake and swamp area :: 0.0 percent 

4 
Table 2. Explanatory variables for the flood-magnitude and -frequency analysis of Main Ditch at the 

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

New Jersey 

Drainage area: 0.55 square miles 

Latitude: 39° 50' 35" 

Longitude: 75° 12' 16" 

Highway: Conrail culvert east of the culvert at New Jersey Route 44 

Milepost: 8.3 

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

Variable Value Unit 

Drainage area = 0.55 square miles 

Main-channel slope = 38.0 feet per mile 

Surface-storage index = 1.0 percent 

Total stream length = 1.19 mile 

Population density (1990) = 1,076 persons per square mile 

Impervious cover = 13 percent 

Lake and swamp area = 0.0 percent 

5 
Table 3. Estimates of flood magnitudes for selected flood frequencies, Main Ditch at the culvert on New 

Jersey Route 44, West Deptford Township, 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: 0,48 square miles 

Latitude: 39° 50' 28" 

Longitude: 75° 12' 03" 

Highway: New Jersey Route 44 

Milepost: 8.3 

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

Estimating method Q2 Q5 Q10 Q25 Q50 Q100 

NJDEPSR 38 66 99 133 186 227 285 

6 
Table 4. Estimates of flood magnitudes for selected flood frequencies, Main Ditch at the Conrail culvert 

downstream from the culvert on New Jersey Route 44, West Deptford Township, 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: 0.55 square miles 

Latitude: 39° 50' 35" 

Longitude: 75° 12' 16" 

Highway: Conrail culvert below New Jersey Rt. 44 

Milepost: 8.3 

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

Estimating method Q2 Q5 QI0 Q25 Q50 Ql00 

NJDEP SR 38 80 120 162 226 276 345 

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, S.1., 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