Flood-Hydrology Data for the Potomac River and Selected Tributaries in the Vicinity of the Chesapeake and Ohio Canal National Historical Park, Maryland, West Virginia, and the District of Columbia

Abstract

This report presents flood-hydrology data for the Potomac River and selected tributaries in the vicinity of the Chesapeake and Ohio Canal National Historical Park (C & O Canal NHP). Data were compiled for the floods of (1) March 17-19, 1936; (2) June 22-24, 1972; (3) November 4-7, 1985; (4) January 19-21, 1996; (5) September 6-8, 1996; and (6) the peak of record for 6 U.S. Geological Survey (USGS) streamflow-gaging stations on the Potomac River and 10 streamflow-gaging stations on selected tributaries to the Potomac River. Peak discharge, peak gage height, the date and time of the peak, and approximate recurrence interval are presented for each flood event at these streamflow-gaging stations.

Data compiled from selected high-flow discharge measurements at the six Potomac River streamflow-gaging stations are presented. The gage height, top width, cross-sectional area, mean velocity, maximum velocity, and discharge are presented for each selected discharge measurement. Any corresponding discharge on the C & O Canal that was measured or estimated during these discharge measurements is presented. Ranges of Manning's roughness coefficient were computed for the range of selected discharge measurements based on estimates of water-surface slope or the channel-bed slope.

An inventory of selected flood studies and reports, and additional USGS data collected along the Potomac River and the C & O Canal NHP also are presented. Included are (1) a listing of selected flood studies and reports, and (2) a listing of USGS indirect flood-discharge measurements that have been made at the six Potomac River streamflow-gaging stations in the vicinity of the C & O Canal NHP. Information on historical streamflow-gaging station records and discharge measurements on the C & O Canal also is presented.

Introduction

The Chesapeake and Ohio Canal National Historical Park (C & O Canal NHP) is operated by the U.S. Department of the Interior, National Park Service (NPS). The park extends from Cumberland, Md., to Georgetown in the District of Columbia. The C & O Canal and its towpath are located well within the flood plain of the Potomac River. The towpath is a historic structure that serves as an important corridor for visitor recreation, including horse, bicycle, and pedestrian uses.

The C & O Canal NHP is often impacted by flooding on the Potomac River. Since being established in January 1971, the park has experienced four major flood events--in June 1972, November 1985, January 1996, and September 1996--causing significant damage to the C & O Canal, towpath, and other park infrastructure. The costs associated with park repairs has risen into the tens of millions of dollars. Flooding and subsequent damage to the C & O Canal NHP has emphasized a need for the NPS to begin (1) correlating park-related flood damage with specific flood events in the Potomac River Basin, (2) predicting expected inundation and subsequent damage based on the magnitude and frequency of flood events, and (3) prioritizing park structures for protection from future flood damage. In order to assist NPS in meeting these objectives, the U.S. Geological Survey (USGS), in cooperation with NPS, initiated a study in November 1996 to (1) compile hydrologic data from specific flood events on the Potomac River and selected tributaries in the vicinity of the C & O Canal NHP, and (2) inventory selected resources and flood-study information along the Potomac River and the C & O Canal NHP.

Purpose and Scope

This report presents hydrologic data on flooding of the Potomac River and selected tributaries to the Potomac River in the vicinity of the C & O Canal NHP. An inventory of selected reports, flood studies, and additional USGS data along the Potomac River and C & O Canal NHP is presented.

This report presents data that were compiled for the floods of (1) March 17-19, 1936; (2) June 22-24, 1972; (3) November 4-7, 1985; (4) January 19-21, 1996; (5) September 6-8, 1996; and (6) the peak of record for 6 USGS streamflow-gaging stations on the Potomac River and 10 USGS streamflow-gaging stations on selected tributaries in the vicinity of the C & O Canal NHP (fig. 1). The peak discharge, peak gage height, the date and time of the peak, and approximate recurrence interval are presented for each flood event.

Data compiled from selected high-flow discharge measurements at the six Potomac River streamflow-gaging stations are presented. Gage height, top width, cross-sectional area, mean velocity, maximum velocity, mean depth, and discharge are presented for each selected discharge measurement. Any corresponding estimates or measurements of discharge on the C & O Canal are also presented for each selected discharge measurement. Ranges of Manning's roughness coefficient (Manning's n) were computed for the range of selected discharge measurements based on estimates of water-surface slope or the channel-bed slope. These data will be used for subsequent hydraulic studies by engineers for maintenance, protection, or restoration of the C & O Canal.

The report also provides an inventory of selected flood studies and reports related to the Potomac River Basin in the vicinity of the C & O Canal NHP. A listing of USGS indirect flood discharge measurements that have been made at the six Potomac River streamflow-gaging stations in the vicinity of the C & O Canal NHP is provided. Information on historical streamflow-gaging station records and discharge measurements on the C & O Canal also is presented.

Acknowledgments

The author would like to thank Patrick L. Toops of the National Park Service, C & O Canal NHP, for planning assistance. Special thanks are extended to the U.S. Geological Survey, West Virginia District, for providing additional data and technical information on streamflow-gaging stations near the Potomac River in West Virginia.

Flood-Hydrology Data for the Potomac River

Flood-hydrology data were compiled for six USGS streamflow-gaging stations on the Potomac River in the vicinity of the C & O Canal NHP. The streamflow-gaging stations are (1) Station 01603000, North Branch Potomac River near Cumberland, Md.; (2) Station 01610000, Potomac River at Paw Paw, W. Va.; (3) Station 01613000, Potomac River at Hancock, Md.; (4) Station 01618000, Potomac River at Shepherdstown, W. Va.; (5) Station 01638500, Potomac River at Point of Rocks, Md.; and (6) Station 01646500, Potomac River at Little Falls near Washington, D.C. Data compiled for these streamflow-gaging stations include (1) basic data regarding the drainage basin and the station, (2) peak-flow data and recurrence intervals for selected flood events, and (3) flow characteristics that were defined in selected discharge measurements made at the stations.

Basic Data

Basic data compiled for each of the six Potomac River streamflow-gaging stations include the (1) latitude and longitude of the station, (2) period of gage record, (3) drainage area at the station, (4) percentage of the total basin drainage area, and (5) mean sea level datum of the station in relation to the National Geodetic Vertical Datum (NGVD) of 1929. This information is listed in table 1.

Peak Flows and Recurrence Intervals

Peak-flow data and approximate recurrence intervals were compiled for the six Potomac River streamflow-gaging stations for the floods of (1) March 17-19, 1936; (2) June 22-24, 1972; (3) November 4-7, 1985; (4) January 19-21, 1996; and (5) September 6-8, 1996. Data for the peak of record also were compiled if the peak occurred during a different flood event than those listed above. The peak-flow data that were compiled included the peak gage height, peak discharge, and the date and time of the peak. An approximate recurrence interval for each event was determined from the station data, and techniques described by the Interagency Advisory Committee on Water Data (1982) and Dillow (1996).

The recurrence interval of a specific flood is the average number of years between floods equal to or greater than that specific flood. It is emphasized that this is an average number of years and does not imply that it will be that many years before another event of that magnitude occurs. Similar or greater events can occur in the same year, as demonstrated by the 1996 floods on the Potomac River. The reciprocal of the recurrence interval is the probability of the event occurring in any one year. For instance, a 100-year flood has a 0.01 probability, or 1 percent chance, of occurring in any year (Lescinsky, 1987).

Peak-flow data and approximate recurrence intervals for the six Potomac River streamflow-gaging stations during the specified flood events are shown in table 2. A flood hydrograph for the streamflow-gaging station on the Potomac River at Point of Rocks, Md., during the flood of January 19-21, 1996, is shown as an example (fig. 2).

Selected Discharge Measurements

Data from selected historical discharge measurements were compiled for the six USGS streamflow-gaging stations on the Potomac River in the vicinity of the C & O Canal NHP. Twelve to thirteen measurements were selected for each streamflow-gaging station that represented a range of high-flow events. The date of the measurement, the sequential measurement number, gage height, top width, cross-sectional area, mean velocity, maximum velocity, mean depth, and discharge are presented for each selected discharge measurement. If any corresponding flow in the C & O Canal was estimated or measured during the measurement, this value also is presented. The maximum velocity is presented in two ways. The section maximum mean velocity is presented as the maximum mean velocity measured in any measurement subsection along the cross section. When discharge measurements are made, the mean velocity in each measurement subsection is determined as the average of point velocities measured at 0.2 and 0.8 of the depth of the subsection at that point, provided that the depth is 2.5 ft or greater at that point. If the depth of the measurement subsection is less than 2.5 ft, the mean velocity for the measurement subsection is determined by measuring a point velocity at 0.6 of the depth of the subsection at that point. The section maximum point velocity is presented as the maximum point velocity measured at any point in any measurement subsection along the cross section. Tables 3 through 8 summarize selected discharge-measurement data for high flows at the six USGS streamflow-gaging stations on the Potomac River in the vicinity of the C & O Canal NHP.

The discharge in a uniform-flow channel can be determined by use of the following empirical formula:

Q = (1.49/n) x (A) x (RH)^2/3 x (S)^1/2

where

Q is the discharge, in cubic feet per second;

n is the dimensionless Manning roughness coefficient, or Manning's n;

A is the cross-sectional area of the channel cross section, in square feet;

RH is the hydraulic radius of the channel cross section, in feet; and

S is the channel-bed slope or the water-surface slope.

Figure 2. Flood hydrograph for U.S. Geological Survey streamflow-gaging station 01638500, Potomac River at Point of Rocks, Maryland, during the flood of January 19-21, 1996.

When uniform flow is assumed in an open channel, the longitudinal lines of the channel bed and water surface are parallel to each other, and the slopes of these parallel lines are equal (Hwang and Hita, 1987). If estimates of water-surface slope or channel-bed slope can be made in the vicinity of a streamflow-gaging station, discharge-measurement data can be used to determine an approximate Manning's n value for the measured flow conditions.

Ranges of Manning's n were calculated for the ranges of discharge and flow conditions presented in tables 3 through 8, based on the assumption of uniform flow conditions. The calculations were made using estimates of water-surface slope that were based on previous flood studies (Somervell, 1930), and flood insurance studies (Federal Emergency Management Agency, 1981, 1985, 1989). Where information on water-surface slope was not available, channel-bed slopes were determined by use of USGS topographic maps. These channel-bed slopes were used as an estimate of water-surface slope. The calculated values of Manning's n apply to the entire cross section that was used during the discharge measurement. Insufficient data exist to calculate Manning's n values for flows in the C & O Canal for these discharge measurements. However, approximations can be made using accepted hydraulic design practices. Table 9 summarizes the general ranges of Manning's n values for the selected discharges and flow conditions presented in tables 3 through 8.

Table 9 shows a large range of Manning's n values for the selected flow conditions at most gaging stations. Direct measurements of water-surface slope during discharge measurements could serve to (1) provide a means to directly calculate Manning's n for any discharge measurement, and (2) provide a means to calibrate the ranges of Manning's n values presented in table 9.

Flood-Hydrology Data for Selected Tributaries

Flood-hydrology data were compiled for 10 USGS streamflow-gaging stations on selected tributaries to the Potomac River in the vicinity of the C & O Canal NHP. The streamflow-gaging stations are (1) Station 01601500, Wills Creek near Cumberland, Md.; (2) Station 01608500, South Branch Potomac River near Springfield, W. Va.; (3) Station 01609000, Town Creek near Oldtown, Md.; (4) Station 01610155, Sideling Hill Creek near Bellegrove, Md.; (5) Station 01611500, Cacapon River near Great Cacapon, W. Va.; (6) Station 01614500, Conococheague Creek at Fairview, Md.; (7) Station 01619500, Antietam Creek near Sharpsburg, Md.; (8) Station 01636500, Shenandoah River at Millville, W. Va.; (9) Station 01643000, Monocacy River at Jug Bridge near Frederick, Md.; and (10) Station 01645000, Seneca Creek at Dawsonville, Md. Data compiled for these streamflow-gaging stations include (1) basic data regarding the drainage basin and the station, and (2) peak-flow data and recurrence intervals for the five selected flood events and the peak of record.

Basic Data

Basic data compiled for each of the 10 Potomac River tributary streamflow-gaging stations include the (1) latitude and longitude of the station, (2) period of gage record, (3) drainage area at the station, (4) percentage of the total basin drainage area, and (5) mean sea level (NGVD) datum of the station. This information is listed in table 10.

Peak Flows and Recurrence Intervals

Peak-flow data and approximate recurrence intervals were compiled for the 10 Potomac River tributary streamflow-gaging stations for the five selected flood events and for the peak of record. For some stations, data were not available for some flood events because the station was not in operation at the time of the specified flood event. Peak-flow data and approximate recurrence intervals for the 10 Potomac River tributary streamflow-gaging stations during the specified flood events are shown in table 11. A flood hydrograph for the streamflow-gaging station at Conococheague Creek at Fairview, Md., during the flood of January 19-21, 1996, is shown as an example (Figure 3).

^a Discharge measured by use of horizontal angle coefficients.
^b Estimated discharge.

^a Discharge adjusted for rapidly changing stage during measurement.
^b Estimated discharge.

^a Measurement was made at Brunswick, Maryland. Gage height and discharge at Point of Rocks were 30.50 ft and 244,000 ft³/s. Discharge for Point of Rocks was determined by correcting measured discharge for storage and inflow between Brunswick and Point of Rocks.

Figure 3. Flood hydrograph for U. S. Geological Survey streamflow-gaging station 01614500, Conococheague Creek at Fairview, Maryland during the flood of January 19-21, 1996.

A list of additional USGS streamflow-gaging stations with surface-water data in the vicinity of the C & O Canal NHP also was prepared. This list is shown in the appendix.

Additional Information and Resources

A search was conducted of (1) the libraries of the USGS Maryland-Delaware-D.C. District office and the Interstate Commission on the Potomac River Basin, and (2) original USGS data files, to compile information and resources related to flooding in the Potomac River Basin in the vicinity of the C & O Canal NHP. Records at these locations are among the most complete available. An inventory of significant flood studies and reports pertaining to the Potomac River Basin in the vicinity of the C & O Canal NHP is presented in the following section. USGS indirect flood-discharge measurements that have been made at the six USGS streamflow-gaging stations on the Potomac River in the vicinity of the C & O Canal NHP also are listed. Information on historical streamflow-gaging station records and discharge measurements on the C & O Canal is summarized.

Flood Studies and Reports

The following inventory of flood studies and reports on the Potomac River Basin in the vicinity of the C & O Canal NHP is sorted by category. Report categories include (1) USGS Annual Water-Resources Data Reports, (2) USGS Water-Supply Papers, (3) other flood studies and reports, and (4) flood-insurance studies.

USGS Annual Water-Resources Data Reports: The USGS releases an annual water-resources data report for each water year, which runs from October 1st of one year to September 30th of the next. For example, October 1, 1996 to September 1, 1997 is referred to as "Water Year 1997". These reports have been published for Maryland and West Virginia on a yearly basis since 1961. The reports summarize flow conditions at all active USGS streamflow-gaging stations for the given water year. This includes such information as mean daily discharges for each day of the water year, mean annual discharge, and the instantaneous peak gage height and discharge at each streamflow-gaging station for the given water year (U.S. Geological Survey, 1961-95).

USGS Water-Supply Papers: Prior to 1961, USGS streamflow-gaging station records were published as part of a report series entitled "Water-Supply Papers." Water-Supply Papers are publications that are intended to present significant interpretive results of hydrologic investigations that are broader than local interest. Specific Water-Supply Papers (WSP) that were used in the preparation of this report include:

1. WSP 800, The Floods of March, 1936, Part III, Potomac, James, and Upper Ohio Rivers (Grover, 1937).
2. WSP 971, Surface Water Supply of the United States, 1943, part 1B, North Atlantic Slope Basins, New York to York River (Parker and others, 1945).
3. WSP 1302, Compilation of Records of Surface Waters of the United States through September, 1950, part 1B, North Atlantic Slope Basins, New York to York River (Wells and others, 1960).
4. WSP 1432, Surface Water Supply of the United States, 1956, part 1B, North Atlantic Slope Basins, New York to York River (Wells and others, 1959).
5. WSP 1672, Magnitude and Frequency of Floods in the United States, part 1B, North Atlantic Slope Basins, New York to York River (Tice, 1968).
6. WSP 1722, Compilation of Records of Surface Waters of the United States, October 1950 to September 1960, part 1B, North Atlantic Slope Basins, New York to York River (Hendricks and others, 1964).

Other Flood Studies and Reports: Often studies are conducted and reports are prepared in the aftermath of major floods. These studies and reports usually document peak gage heights and peak discharges for streamflow-gaging stations during a specific flood event. Some studies and reports may present estimated flood profiles for specific flood events or for flood events of a certain magnitude or frequency. Others may contain descriptive material about specific flood events. The subjects and authors of notable studies and reports related to flooding in the Potomac River Basin in the vicinity of the C & O Canal NHP are listed below in chronological order.

1. Development of Great Falls for Water Power and Increase of Water Supply for the District of Columbia (U.S. Army Corps of Engineers, 1921).
2. Report to the Chief of Engineers, U.S. Army on the Potomac River and its Tributaries, Including Occoquan Creek (Somervell, 1930).
3. Floods of 1936 and 1937 (Pennsylvania Railroad Company, 1937).
4. Flow Data and Draft Storage Curves for Major Streams, 1929-1937 (Maryland Water Resources Commission, State Planning Commission, 1940).
5. Storm and Flood of October 16, 17, 18, 1942 (U.S. Army Corps of Engineers, 1942).
6. Joint Reconnaissance Survey and Study of the Chesapeake and Ohio Canal, Between Great Falls, Maryland and Cumberland, Maryland (Bureau of Public Roads and National Park Service, 1950).
7. Storms and Floods of August, 1955 (U.S. Army Corps of Engineers, 1955).
8. The Water Resources of Carroll and Frederick Counties (Beall and Meyer, 1958).
9. Maryland Streamflow Characteristics; Flood Frequency, Low Flow Frequency, and Flow Duration (Darling, 1962).
10. Tropical Storm Agnes--June, 1972, Basins of the Susquehanna and Potomac Rivers and Maryland Portions of Chesapeake Bay and Atlantic Coast, Post Flood Report, Volume 1, Meteorology and Hydrology (Prepared by Gannett, Fleming, Corddry, and Carpenter Engineers for the U.S. Army Corps of Engineers, Baltimore District, 1974).
11. Flood Plain Information, Frederick County, Potomac River, Maryland (U.S. Army Corps of Engineers, 1975).
12. USGS Professional Paper 924, Hurricane Agnes Rainfall and Floods, June-July, 1972 (Bailey and others, 1975).
13. Historic Structure Report, Chesapeake and Ohio Canal Dam Number 2 and Associated Structures (Unrau, 1976a).
14. The Major Floods of the Potomac River and Their Effect on the Chesapeake and Ohio Canal: 1828-1936 (Unrau, 1976b).
15. Tropical Storm Eloise, September, 1975, Susquehanna and Potomac River Basins, Post Flood Report (U.S. Army Corps of Engineers, 1976).
16. Flood Plain Information, Washington County, Potomac River, Maryland, Part 1, (U.S. Army Corps of Engineers, 1977).
17. Floodplain Reconnaissance Study, November 1985 Flood, Potomac River Basin (Scatena, 1986).
18. USGS Open-File Report 86-486, Flood of November, 1985 in West Virginia, Pennsylvania, Maryland, and Virginia (Lescinsky, 1987).
19. USGS Water-Resources Investigations Report 88-4213, Floods in West Virginia, Virginia, Pennsylvania, and Maryland, November 1985 (Carpenter, 1988).
20. C & O Canal: The Making of a Park (MacKintosh, 1991).

Most of these studies and reports provide hydrologic data, peak-flow data or descriptive information for certain flood events. A few of the U.S. Army Corps of Engineers' publications provide flood profiles for certain flood events or cross sections of the Potomac River in various locations.

Flood-Insurance Studies: The Federal Emergency Management Agency (FEMA) publishes flood-insurance studies for Maryland counties and some specific towns and communities along the Potomac River. The reports for these studies contain various hydrologic and hydraulic data for streams and rivers within the study area. Cross-sectional data are usually obtained from USGS topographic maps or from field surveys. Hydraulic data and flood profiles are usually determined by use of step-backwater hydraulic modeling. Most FEMA flood-insurance studies present drainage areas, peak-flow data, and recurrence-interval information, as of the most recent date that the information was updated. Channel widths, cross-sectional areas, and mean velocities are presented for different segments of each stream or river that is studied. Flood profiles are presented for each stream or river that is studied for the 10-year, 50-year, 100-year, and 500-year recurrence intervals.

FEMA flood-insurance studies for counties and towns in the vicinity of the C & O Canal NHP include the Town of Hancock, Md. (FEMA, 1981), the City of Cumberland, Md. (FEMA, 1983), the District of Columbia (FEMA, 1985), and Allegany County, Md. (FEMA, 1989). These reports contain data and flood profiles for the North Branch Potomac River and Potomac River. Reports are available for Frederick County, Md. (FEMA, 1991), Washington County, Md. (FEMA, 1992a), and Montgomery County, Md. (FEMA, 1992b), but data and flood profiles for the Potomac River are not included in these reports. A flood-insurance report was published for the Town of Williamsport, Md. (U.S. Department of Housing and Urban Development, Federal Insurance Administration, 1976), but was not available for review.

Indirect Flood-Discharge Measurements

The discharge of streams and rivers is usually measured directly using a current meter. During floods, however, it is sometimes impossible or impractical to measure the discharge by this method. Consequently, some peak discharges must be determined after the passage of the flood by indirect methods, such as slope-area, contracted-opening, flow-over-dam, and flow-through-culvert, rather than by direct current-meter measurement (Benson and Dalrymple, 1967).

Indirect methods of determining flood discharge are based on hydraulic equations which relate the discharge to the water-surface profile and geometry of the channel. A field survey is made after the flood to determine the location of high-water marks and the physical characteristics of the channel (Benson and Dalrymple, 1967). Hydraulic equations that are most appropriate for the study reach are then solved based on the field data to determine the peak discharge for the study reach.

Indirect flood-discharge measurements can provide information such as (1) records of high- water marks, (2) cross-section geometry and diagrams, (3) estimates of Manning's n, and (4) calculations of water-surface slopes. The data files of the USGS Maryland-Delaware-D.C. District were searched to inventory indirect flood-discharge measurements that have been made at the six USGS streamflow-gaging stations on the Potomac River in the vicinity of the C & O Canal NHP. The results of the search are listed below.

Station 01603000, North Branch Potomac River near Cumberland, Md.--An indirect measurement of peak discharge was made for the flood of March 17-19, 1936. The peak discharge was determined to be 88,200 ft³/s, including documentation of flow in the overbank areas.

Station 0161000, Potomac River at Paw Paw, W. Va.--An indirect measurement of peak discharge was made for the flood of March 17-19, 1936. The peak discharge was determined to be 240,000 ft³/s, including documentation of flow in the overbank areas and the C & O Canal. The results indicated that a peak discharge of approximately 3,000 ft³/s was carried in the C & O Canal for this event.

Station 01613000, Potomac River at Hancock, Md.--An indirect measurement of peak discharge was made for the flood of March 17-19, 1936. The peak discharge was determined to be 340,000 ft ³s, including documentation of flow in the overbank areas and the C & O Canal. The results indicated that a peak discharge of approximately 1,700 ft³s was carried in the C & O Canal for this event.

An indirect measurement of peak discharge was also made for the flood of April 27, 1937. The peak discharge was determined to be 153,000 ft³s, including documentation of flow in the overbank areas. The flow for this event did not overtop the C & O Canal as it did in March 1936. However, the water surface at the peak was nearly level with the top of the towpath.

Station 01618000, Potomac River at Shepherdstown, W. Va.--High watermarks were documented for the flood of April 27, 1937. An indirect measurement of peak discharge was made for the flood of October 16-18, 1942. The results indicated a peak discharge of 190,000 ft³s, including documentation of flow in the overbank areas and the C & O Canal. Estimates of flow in the C & O Canal ranged from 1,280 ft³/s to 1,780 ft³/s depending on the location and hydraulic characteristics of the measured cross sections.

Station 01638500, Potomac River at Point of Rocks, Md.--An indirect measurement of peak discharge was made for the flood of March 17-19, 1936. The peak discharge was determined to be 480,000 ft³/s, including documentation of flow in the overbank areas and the C & O Canal. Estimates of flow in the C & O Canal ranged from 1,700 ft³/s to 3,630 ft³/s depending on the location and hydraulic characteristics of the measured cross sections.

Streamflow-Gaging Stations on the Chesapeake and Ohio Canal

The USGS previously operated two streamflow-gaging stations on the C & O Canal. Streamflow-gaging station 01602000, on the C & O Canal at Cumberland, Md., was in operation from October 1929 to September 1934. Streamflow-gaging station 01620000, on the C & O Canal at Point of Rocks, Md., was in operation from August 1931 to November 1935.

Data and related information that are available for these streamflow-gaging stations include (1) mean daily discharges, (2) summaries of discharge measurements, (3) rating curves and tables of gage height versus discharge that were valid during the period of record, and (4) descriptions of the stations and their locations. The maximum known discharge and gage height during the period of record for the streamflow-gaging station on the C & O Canal at Cumberland, Md., was 104 ft³/s at a gage height of 9.85 ft on May 16, 1930. This maximum discharge did not occur during a flood event on the North Branch Potomac River. The maximum known discharge and gage height during the period of record for the streamflow-gaging station on the C & O Canal at Point of Rocks, Md., was 146 ft³/s at a gage height of 2.64 ft (approximately 227.64 ft above sea level) on May 13, 1932. This maximum discharge occurred during a flood event on the Potomac River during May 13 and 14, 1932. The peak discharge and gage height at streamflow-gaging station 01638500 (Potomac River at Point of Rocks) were 158,000 ft³/s and 23.34 ft (223.97 ft above sea level), respectively. The recurrence interval for this flood event was approximately 5 years.

Other Discharge Measurements on the Chesapeake and Ohio Canal

Between 1923 and 1995, over 250 discharge measurements were made on the C & O Canal at several locations. Many of these discharge measurements were made in the vicinity of the Potomac River at Chain Bridge because the C & O Canal diverts flow from the Potomac River at this location. Since discharge measurements for station 01646500, Potomac River at Little Falls near Washington, D.C., are often made at Chain Bridge, the diversion of flow from the Potomac River requires an estimate or measurement of flow in the C & O Canal at this location to obtain the total discharge. Other locations where discharge measurements have been made on the C & O Canal include Cumberland, Md.; Hancock, Md.; Harpers Ferry, W. Va.; and Brunswick, Md. These discharge measurements document the same types of data variables that were presented for the Potomac River streamflow-gaging stations in tables 3 through 8, including the channel width, cross-sectional area, mean and maximum velocities, and discharge.

Summary

This report presents flood-hydrology data for the Potomac River and selected tributaries in the vicinity of the Chesapeake and Ohio Canal National Historical Park. Data were compiled for selected flood events at 6 USGS streamflow-gaging stations on the Potomac River and 10 streamflow-gaging stations on selected tributaries to the Potomac River. Peak discharge, peak gage height, the date and time of the peak, and approximate recurrence interval are presented for each flood event at these streamflow-gaging stations.

Data compiled from selected high-flow discharge measurements on the six Potomac River streamflow-gaging stations are presented. The gage height, top width, cross-sectional area, mean velocity, maximum velocity, and discharge are presented for each selected discharge measurement. Any corresponding discharge on the C & O Canal that was measured or estimated for these discharge measurements is presented. Ranges of Manning's n were computed for the range of selected discharge measurements based on estimates of water-surface slope or the channel-bed slope.

An inventory of flood studies, reports, and additional USGS data collected along the Potomac River and the C & O Canal NHP is also presented. Included are (1) a listing of selected flood studies and reports, and (2) a listing of USGS indirect flood-discharge measurements that have been made at the six Potomac River streamflow-gaging stations in the vicinity of the C & O Canal NHP. Information on historical streamflow-gaging station records and discharge measurements on the C & O Canal is also presented.

References Cited

Bailey, J.F., Patterson, J.L., and Paulhus, J.L.H., 1975, Hurricane Agnes rainfall and floods, June-July 1972: U.S. Geological Survey Professional Paper 924, 403 p.

Beall, R.M., and Meyer, Gerald., 1958, The water resources of Carroll and Frederick Counties: State of Maryland, Board of Natural Resources, Department of Geology, Mines, and Water Resources, Bulletin 22, 355 p.

Benson, M.A., and Dalrymple, Tate, 1967, General field and office procedures for indirect discharge measurements: U.S. Geological Survey Techniques of Water-Resources Investigations, book 3, chap. A1, 30 p.

Bureau of Public Roads and National Park Service, 1950, Joint reconnaissance survey and study of the Chesapeake and Ohio Canal, between Great Falls, Maryland, and Cumberland, Maryland: Washington, D.C., House Document No. 687, 81st Congress, 2nd Session, 87 p.

Carpenter, D.H., 1988, Floods in West Virginia, Virginia, Pennsylvania, and Maryland, November 1985: U.S. Geological Survey Water-Resources Investigations Report 88-4213, 86 p.

Darling, J.M., 1962, Maryland streamflow characteristics: Flood frequency, low flow frequency, and flow duration: State of Maryland, Board of Natural Resources, Department of Geology, Mines and Water Resources, Bulletin 25, 136 p.

Dillow, J.J. A., 1996, Technique for estimating magnitude and frequency of peak flows in Maryland: U.S. Geological Survey Water-Resources Investigations Report 95-4154, 55 p.

Federal Emergency Management Agency, 1981, Flood insurance study, Town of Hancock, Maryland, Washington County: Federal Emergency Management Agency, Washington, D.C., 15 p.

_____ 1983, Flood insurance study, City of Cumberland, Maryland, Allegany County: Federal Emergency Management Agency, Washington, D.C., 35 p.

_____ 1985, Flood insurance study, District of Columbia: Federal Emergency Management Agency, Washington D.C., 23 p.

_____ 1989, Flood insurance study, Allegany County, Maryland, Unincorporated areas, Volume 1 of 2: Federal Emergency Management Agency, Washington D.C., 48 p.

_____ 1991, Flood insurance study, Frederick County, Maryland, Unincorporated areas: Federal Emergency Management Agency, Washington D.C., 56 p.

_____ 1992a, Flood insurance study, Washington County, Maryland, Unincorporated areas: Federal Emergency Management Agency, Washington D.C., 67 p.

_____ 1992b, Flood insurance study, Montgomery County, Maryland, Unincorporated areas, Volume 1 of 6: Federal Emergency Management Agency, Washington D.C., 155 p.

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Grover, N.C., 1937, The floods of March 1936; Part 3; Potomac, James, and Upper Ohio Rivers: U.S. Geological Survey Water-Supply Paper 800, 351 p.

Hendricks, E.L., and others, 1964, Compilation of records of surface waters of the United States, October 1950 to September 1960, Part 1-B, North Atlantic slope basins, New York to York River: U.S. Geological Survey Water-Supply Paper 1722, p. 451-546.

Hwang, N.H.C., and Hita, C.E., 1987, Fundamentals of hydraulic engineering systems: Englewood Cliffs, N.J., Prentice-Hall, Inc., 370 p.

Interagency Advisory Committee on Water Data, 1982, Guidelines for determining flood flow frequency: Water Resources Council Bulletin 17B, 28 p.

Lescinsky, J.B., 1987, Flood of November 1985 in West Virginia, Pennsylvania, Maryland, and Virginia: U.S. Geological Survey Open-File Report 86-486, 33 p.

MacKintosh, Barry, 1991, C & O Canal: The Making of a Park: Washington D.C., History Division, National Park Service, U.S. Department of the Interior, 208 p.

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Parker, G.L., and others, 1945, Surface water supply of the United States, 1943, Part 1, North Atlantic slope basins, New York to York River: U.S. Geological Survey Water-Supply Paper 971, p. 538-585.

Pennsylvania Railroad Company, 1937, Floods of 1936 and 1937: Philadelphia, Pa., Cuneo Eastern Press, 150 p.

Scatena, F.N., 1986, Floodplain reconnaissance study, November 1985 flood, Potomac River Basin: Baltimore, Md., The Johns Hopkins University, 45 p.

Somervell, Brehon, 1930, Report to the Chief of Engineers, U.S. Army, on the Potomac River and its tributaries including Occoquan Creek, Volume 2, Section 2: United States Engineer Office, Washington, D.C., 178 p.

Taylor, K.R., James, R.W., Jr., and Helinsky, B.M., 1984, Travel time and dispersion in the Potomac River, Cumberland, Maryland, to Washington, D.C.: U.S. Geological Survey Open-File Report 83-861, 55 p.

Tice, R.H., 1968, Magnitude and frequency of floods in the United States, Part 1-B, North Atlantic slope basins, New York to York River: U.S. Geological Survey Water-Supply Paper 1672, 585 p.

U.S. Army Corps of Engineers, 1921, Development of Great Falls for water power and increase of water supply for the District of Columbia: Government Printing Office, Washington, D.C., 179 p.

______ 1942, Storm and flood of October 16, 17, 18, 1942: Office of the District Engineer, U.S. Army Corps of Engineers, Washington, D.C., 18 p.

_____ 1955, Storms and floods of August 1955: Office of the District Engineer, U.S. Army Corps of Engineers, Washington, D.C., 14 p.

_____ 1975, Flood plain information, Frederick County, Potomac River, Maryland: U.S. Army Corps of Engineers, Baltimore District, Baltimore, Md., 22 p.

_____ 1976, Tropical Storm Eloise, September 1975, Susquehanna and Potomac River Basins post flood report: U.S. Army Corps of Engineers, Baltimore District, Baltimore, Md., 40 p.

_____1977, Flood plain information, Washington County, Potomac River, Maryland, Part 1: U.S. Army Corps of Engineers, Baltimore District, Baltimore, Md., 24 p.

U.S. Department of Housing and Urban Development, Federal Insurance Administration, 1976, Flood insurance study, Town of Williamsport, Washington County, Maryland: Washington D.C., variously paged.

U.S. Geological Survey, 1962-65, Surface water records of Maryland and Delaware, water years 1961-64; U.S. Geological Survey Water-Data Reports MD-61 to MD-64 (published annually).

_____ 1966-75, Water resources data for Maryland and Delaware, 1965-74--Part 1. Surface-water records: U.S. Geological Survey Water-Data Reports MD-65-1 to MD-74-1 (published annually).

_____ 1976-89, Water resources data, Maryland and Delaware, water years 1975-88; U.S. Geological Survey Water-Data Reports MD-75-1 to MD-88-1 (published annually).

_____ 1990-91, Water resources data, Maryland and Delaware, water years 1989-90, Volumes 1 and 2; U.S. Geological Survey Water-Data Reports MD-DE-89 to MD-DE-90 (published annually).

_____ 1992-96, Water resources data, Maryland and Delaware, water years 1991-95--Volume 1. Surface-water data: U.S. Geological Survey Water-Data Reports MD-DE-91-1 to MD-DE-95-1 (published annually).

Unrau, H.D., 1976a, Historic structure report, Chesapeake and Ohio Canal Dam Number 2 and associated structures: Denver, Co., Historic Preservation Division, National Park Service, Denver Service Center, 84 p.

______ 1976b, The major floods of the Potomac River and their effect on the Chesapeake and Ohio Canal: 1828-1936, Chapter 10; Chesapeake and Ohio Canal National Historical Park Historic Resource Study: Denver, Co., National Park Service, Denver Service Center, 288 p.

Wells, J.V.B., and others, 1959, Surface water supply of the United States, 1956, Part 1-B, North Atlantic slope basins, New York to York River: U.S. Geological Survey Water-Supply Paper 1432, p. 463-557.

Wells, J.V.B., and others, 1960, Compilation of records of surface waters of the United States through September 1950, Part 1-B, North Atlantic slope basins, New York to York River: U.S. Geological Survey Water-Supply Paper 1302, p. 552-648.

Appendix

¹ Station contains other shorter periods of record prior to current period of record.