3,000 cubic feet per second: 1 time a year
4,000 cubic feet per second: 3 times a year
6,500 cubic feet per second: 18 times a year
8,000 cubic feet per second: 40 times a year
10,000 cubic feet per second: 100 times a year

Other articles relating to floods in the Frankford Creek, found by Adam Levine:
September 25, 1882, two articles (627 Kb and 5 kb)
November 1, 1932 (80 Kb)
August 18, 1938 (142 Kb)

Flood Characteristics.

The dates mentioned in the preceding paragraphs [page 21] indicate that the greatest floods on Frankford Creek have not occurred in the spring and fall as on large rivers like the Delaware, but have occurred in the summer months as a result of intense thunderstorms or so-called cloudbursts. Thunderstorms are generally localized and may cover an area only a few miles in length and breadth. For example, summer floods have occurred on Frankford Creek when little or no rainfall was recorded in downtown Philadelphia. Local storms that moved across the drainage area in a direction from northwest to southeast appear to have caused the most severe floods. Some of the floods have been caused by general rains brought in by intense tropical storms or hurricanes. These latter storms occur in the summer or early fall. The present development of the Frankford Creek drainage area has undoubtedly changed the characteristics of the floods. Observations in the field and theoretical studies indicate that in time of flood the creek rises very rapidly, possibly 10 feet in an hour, and that it reaches an initial peak in one to two hours. This type of flash flooding is caused by the runoff from about 15 square miles of sewered area above Juniata. Park. The flood runoff from the remaining drainage area in Montgomery County is slower and causes a second and lower peak about 3 hours later than the first peak.

Although the construction of buildings, paved streets and storm sewers tends to increase the rapidity of runoff and the frequency of minor floods, it has certain advantages insofar as flood control for the creek is concerned. For example, it is not practicable from an engineering standpoint or justifiable from an economic standpoint to design sewer inlets and discharge lines to pass immediately the peak runoff from very rare storms. Following such storms the rate of discharge from a sewered area is limited by the capacity of the sewer system and as a result temporary ponding may occur in streets and at low points. Therefore, the peak rate of runoff from a developed area [page 22] may be less than from an equivalent undeveloped area. This condition exists in the lower portion of the Frankford Creek watershed where the total ultimate capacity of the sewer system will limit the peak discharge to 10,400 cfs. This is a large discharge compared with the greatest flood of record (6,500 cubic feet per second) but may ultimately occur.

A flood on the creek may result from contributions of runoff from both the City sewered area and the County suburban area but there is little chance of both areas contributing maximum discharges in coincidence. There is also little chance, that even if a severe storm centered on the suburban area, the resulting peak discharge from that area alone would exceed the maximum recorded flood on Frankford Creek. The reason for the latter statement is that there are three street bridges (Adams Avenue, Rising Sun Avenue, and Fisher's Lane) and one railroad culvert (Reading Railroad) with moderate sized waterway openings that would tend to throttle discharges of more than about 5,000 cubic feet per second. The throttling action of the bridges would cause ponding in the park areas upstream, further modifying the flood runoff and delaying the time of travel.

The above discussion indicates that, although the lower reaches of Frankford Creek will continue to have floods in excess of the present channel capacity, there are certain features of the present upstream development that act to reduce overwhelming floods such as can occur on natural areas of equivalent size.

Tidal Inundation.

High tides or a combination of high tides and flood flows in the Delaware River have several times caused flooding in the lower reaches of Frankford Creek below Orthodox Street. A combination of high tides and runoff from Frankford Creek have caused flooding between Orthodox Street and Frankford Avenue.

[page 23] The highest tide of record occurred on August 24, 1933, at the time of a tropical hurricane. The crest of this tide at the mouth of the creek was 5.5 feet above normal high tide. The rains accompanying the hurricane caused one of the highest known floods in the upper reaches of Frankford Creek on August 23. It is estimated that the peak of the flood in the creek occurred when the tide was 3 feet above normal high tide. The flooding from the combination of causes was probably the worst ever experienced for a distance of about 2 miles above the mouth of the creek.

Two other periods of flooding at the mouth of Frankford Creek occurred at times of abnormal tides in combination with floods in the Delaware River. The peaks of these two floods occurred on October 11, 1903, and March 19-21, 1936, and reached elevations about 4 feet above normal high tide. Normally there is no slope in the Delaware River at the mouth of Frankford Creek, but there is appreciable slope during very high floods such as those mentioned above. Because of this absence of slope, the elevation of the tide at the mouth of the creek is normally the same as at Chestnut Street in downtown Philadelphia. The tide at Frankford Creek lags the tide at Chestnut Street by about half an hour.

Any plan of flood protection for the creek must take into account tidal effects and their combination with flood runoff in the upper creek.

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