Fig. 62—Beach cusps extended under water and showing the interference of waves off the curved beach on the bay side north of Beach Haven, N. J. Scale, about 1:3,000.
Fig. 63—First stage in the formation of an inlet through a barrier beach, where ocean waves during some storm, probably at high tide, broke over the sand barrier 2 miles north of Beach Haven, N. J., and washed some of its sand into Little Egg Harbor. (For another good example of wash-overs, see Fig. 68.) Scale, about 1:9,000.
Fig. 64—A tidal delta in Shark River Inlet, Belmar, N. J., as photographed from a height of 10,000 feet, showing shoals at the left, which appear shadowy because they are under water, and the small channels which radiate outward from the narrow inlet like the ribs of a fan. They are the distributaries of this underwater delta. Scale, about 1:11,000.
Use in Coast Charting
Fig. 65—A tidal delta built up until it is partly above water: Popes Creek, Virginia, on the right bank of the lower Potomac River, 4 miles southeast of Colonial Beach, as seen obliquely from a height of 4,000 feet at 3:30 P.M., August 31, 1920. The tidal currents from the Potomac have built hook-shaped bars nearly across the outlet of the creek, and the inflowing currents have built a delta from the mouth of the creek upstream.
It is fortunate for those engaged in the study of shore features and the mapping of coasts that, being flat, shore features are particularly well adapted to representation by air photographs, for on coasts exposed to the wind and waves the channels, shoals and bars are continually changing. Air photography offers a quick and convenient means of keeping charts up to date. The intricacies of the water line in some places makes accurate charting by the ordinary survey methods a slow, laborious process. When bluffs or relatively steep slopes, like those of York River, Virginia, near Gloucester Point, shown in Figure 60,
Fig. 66—A double tidal delta at Barnegat Inlet, New Jersey, as photographed from a height of 10,000 feet. To the east (right) the breaking waves and shadowy depths indicate the position of shoals. West of the surf belt are the light-colored beach sand, shading off from the conspicuous hook at the southern end of Island Beach into underwater shoals and bars, and older surfaces made dark-colored by the growth of plants. South of the hook are the inlet leading into Barnegat Bay and the northern end of Long Beach, at the point of which stands a lighthouse whose long shadow is to be seen across the beach sand. The mottled appearance of the bay to the left is due to shoals slightly submerged or perhaps exposed at low tide, where dark-colored drainage lines appear, and shading off to deeper water, where the submerged land forms have a shadowy appearance. The distribution of the shoals indicates that this is a double tidal delta, an infacing part west of the inlet and an ocean-facing part to the right. Scale, about 1:17,000.
Fig. 67 Fig. 67—A tidal inlet through the barrier beach south of Beach Haven, N. J., connecting the Atlantic Ocean to the right (east) with Little Egg Harbor to the left. The beach sand south of the inlet is little above water level and is frequently washed by waves, which shift the sand and produce the clouded appearance of the sandy surface. The light-colored ragged belt at the right is surf; the continuous narrow belt, beach sand; the clouded areas, recently washed wet or slightly submerged sand. (The ordinary tidal variation here is 4.2 feet.) This inlet does not appear on the 1914 edition of U. S. Coast and Geodetic Survey Chart 1216, and sand hooks had little more than begun to form then. Scale, about 1:14,000.
Fig. 68—Beach between Brigantine and Little Egg Inlets, New Jersey, showing a variety of features characteristic of a wave-built sand barrier. The upper (northern) part of the illustration shows several places where waves have broken over the sand barrier and washed the sand westward, where it was redeposited at the left in the quiet, protected water. Farther south are older wash-overs, where the enclosed bay is nearly filled with sand. At the left are numerous islands, streams, and flats characteristic of the salt marshes west of the barrier beach along the New Jersey coast. Scale, about 1:7,000.
Fig. 68—Beach between Brigantine and Little Egg Inlets, New Jersey, showing a variety of features characteristic of a wave-built sand barrier. The upper (northern) part of the illustration shows several places where waves have broken over the sand barrier and washed the sand westward, where it was redeposited at the left in the quiet, protected water. Farther south are older wash-overs, where the enclosed bay is nearly filled with sand. At the left are numerous islands, streams, and flats characteristic of the salt marshes west of the barrier beach along the New Jersey coast. Scale, about 1:7,000.
Fig. 69—A simple spit: Lower Cedar Point, Maryland, on the left bank of the lower Potomac River, 6 miles north of Colonial Beach, Va., as seen obliquely downward from a height of 4,000 feet. The white line on either side of the point is sand at the foot of bluffs. Houses and fields are seen at the left.
occur along the shore, the water line varies little from year to year. But on very low lands, like those along Chesapeake Bay south of the mouth of York River, shown in Figure 59, the strand may migrate over a broad belt between high and low tide. For this reason it is desirable that photographs of areas affected by the tide be accompanied by a record of the date and time of day at which the exposure was made, in order that the height of the tide at the time of exposure can be computed. As the shore on the Coast and Geodetic Survey charts denotes the water line at high tide, a photograph taken at low tide might be interpreted as indicating an error on the chart. Where the water migrates over such a broad belt of sand or mud, the problems of charting become very troublesome. Photographs of such areas could be taken at both low and high tide, and from these the belt of daily flooding could be charted.
Fig. 70—A hook, or recurved spit, south of Brigantine Inlet, New Jersey, as photographed from a height of 10,000 feet, showing the strong curving upstream characteristic of spits on this ocean-facing coast. The growing end of the spit, resembling a lily bud, shows an underwater extension beyond the light-colored beach sand. To be noted is the filling in of the lagoon behind the reef and its pools and drainage lines. This figure is practically a southern continuation of Fig. 68. Scale, about 1:9.000.
Experiments by the United States, French, And Other Coast Surveys
The use of photographs in charting the coast line was tested by the United States Coast and Geodetic Survey.[11] A flight was
Fig. 71—A hook, or recurved spit, showing interference with natural growth: The northern end of Ocean City. N. J., as photographed from a height of 10,000 feet. At the right (east) appears the curved body of sand, light-colored where dried, darker-colored where bathed by the waves and fringed by surf. To the left certain “improvements” seem to have interfered with the natural growth of the spit, and a small bay of shallow water has been enclosed by the formation of a bay-mouth bar across the outlet to the north. Scale, about 1:14,000.
made over the coast of New Jersey by Captain A. W. Stevens of the United States Army Air Service, March 20, 1920, in a plane equipped with a K-1 camera of 10-inch focal length, which makes negatives 18 by 24 centimeters in size. During the flight the camera was maintained at an altitude of about 10,000 feet. The course was covered by 183 exposures made at such intervals of time that the prints overlap. Unfortunately the exposures were not sufficient to give all the details desired for marsh and water areas, but prints were made on developing paper suitable for showing extreme contrast. These were matched together and a continuous picture obtained. A part
Fig. 72—New Point Comfort, a complex recurved spit at the tip of the peninsula enclosed by the York and Rappahannock Rivers, Virginia. A vertical view taken from an altitude of about 10,000 feet, showing in order from right to left (east to west): the wavy surface of Chesapeake Bay; a light-colored band of beach sand curving westward in a compound hook made dark-colored in some places by trees and brush; a shallow bay west of the beach in which may be seen shoals, channels, and sand bars under water; and low-lying areas showing woodland and cultivated fields. The photograph was taken at a time of day when reflected light from the partly enclosed body of water was dispersed, allowing the submerged forms to appear. Scale, about 1:12,000.
Fig. 73—Lines of growth in a sand spit: Tucker Beach, New Jersey, as photographed from a height of 10,000 feet, showing the growth southward by successive ridges, which probably began as sand bars, grew to be barriers by wave action, were heightened by wind-blown sand, and finally were added to the main body of the spit by the final filling of the enclosed lagoons. To the right (east) is the Atlantic Ocean, showing waves and surf near the light-colored beach sand. Farther to the left are the ridges of sand made dark-colored by vegetation, bordered by light-colored beach sand on Little Egg Inlet, which appears to the south and west. Scale, about 1:14,000.
of this picture, greatly reduced, is reproduced as Figure 22. Several characteristic shore and salt marsh features are illustrated by this series of photographs, and these are reproduced in separate figures together with illustrations of special features in other places.
Fig. 74—An island developing toward the stage of being tied to the mainland by a double tombolo, or connecting bar: Napatree Point, as photographed from a height of about 10,000 feet, connected to the east by Napatree Beach with the mainland at Watch Hill, R. I., and approaching connection to the north with the mainland near Stonington, Conn. On the outer side of the tombolos underwater shoals and bars are seen dimly at the right (south, Block Island Sound side) and more clearly at the left (west, Fishers Island Sound), where the boat landing is situated at the edge of a submerged shelf. The surf appears as a thin white line, the beach sand as a narrow light-colored belt, and the higher land as dark-colored areas on which houses and other structures stand. Scale, about 1:24,000.
The main features illustrated in detail, all of which are continually liable to change, making the keeping of a map of the area at all up to date impossible by ordinary means, are as follows: coast of low-lying mainland (Fig. 60); mud or peat-covered beach (Fig. 59); sandy beach (Fig. 63); barrier beach (Fig. 67); beach cusps (Figs. 61 and 62); recurved spits or sand hooks (Fig. 70 and others); compound hook (Fig. 72); lines of growth in the development of hooks (Figs. 73); tombolos and tied islands (Figs. 60 and 74).
Fig. 75—Oblique view of the mouth of Powells Creek, Virginia, on the right bank of the lower Potomac River, 5 miles west of the Naval Proving Grounds at Indian Head, showing at the left the inner channel winding through the slightly submerged shoals and fading out toward the right where the channel crosses the submerged terrace of the Potomac.
Another experiment was made by the Coast and Geodetic Survey off the coast of Florida, where the water is clear, in an attempt to photograph “the small coral heads and pinnacle rocks” which may be disastrous to boats. The report states that the results were unsatisfactory and concludes that airplane pictures are useful in “aerial photo-topography” but not in
Fig. 76—Channels, shoals, and terraces in a drowned river valley: Roberts Creek, 9 miles southeast of Yorktown, Va., an estuary tributary to Chesapeake Bay. Under the water in the drowned valley is seen the channel, “braided” in some places, and extending out through sand bars to the deep water of Poquoson River shown at the top (north) of the illustration. At the left the dark-colored forest area is fringed with a narrow strip of white beach sand, then with a belt of shallow water at the outer edge of which the waves form an irregular white line, and beyond this with a belt which represents a submerged terrace. Scale, about 1:14,000.
Fig. 77—The underwater channel in Quantico Bay. Quantico Creek is a tributary of the Potomac River entering from the Virginia side, about 28 miles downstream from Washington. The “Bay” is the widened part of the stream at its entrance into the Potomac, which is entered by the tide. Forested land appears at the right and left, with light-colored fields at the left. The space between the wooded areas is occupied by shallow water, beneath which appears the relatively deep channel, which forks after the manner of streams. The branching channel is wholly under water and differs in some respects from the channel of a normal stream. Among the more obvious peculiarities is the “fanning out,” of the headwaters. Photograph taken from a height of about 18,000 feet. Scale, about 1:21,000.
Fig. 78—Natural channels and shoals near Miami, Fla.: an oblique view eastward to the ocean across Bear’s Cut, which is situated between Biscayne Key and Virginia Key. Because of the greater depth of water, the channels with a maximum depth of 17 feet appear darker than the shoals. The photograph was taken at a height of 3,000 feet, April 20, 1918.
Fig. 79—A dredged channel at Miami, Fla.: an oblique photograph showing part of the city, the boat landing, the sandy beach, and the shallow water, through which a straight ship channel has been cut, which appears dark-colored in the illustration because of the greater depth of water. The photograph was taken April 22, 1918, from 21 height of 3,000 feet.
Fig. 80—A shoal in Hereford Inlet north of Wildwood, N. J., as seen from a height of 10,000 feet. The breaking waves indicate that the shoal is only slightly submerged. (Tidal variation is here about 4 feet.) The sand spit north of the shoal, the south end of Sevenmile Beach, like other spits of the New Jersey coast, is building southward and may in time annex the shoal. Scale, about 1:13,000.
Fig. 81—Sand bars at Cape Charles, Va. South of the town at the right is the harbor, into which a tug-boat is towing a barge. West of the town (left) is a belt of light-colored beach sand and sand bars ending at the south against the breakwater, north of the harbor. The sand bars appear somewhat dim because they were photographed through water. They are under water 1 to 6 feet deep at low tide, or 4 to 9 feet at high tide. Scale, about 1:6,000.
“aerial photo-hydrography.”[12] On the other hand, Volmat reports the successful use of air photography for similar purposes on the French coast, where photographs of objects down to a depth of 17 meters (about 56 feet) were found useful in several ways—among others, the discovery of points of rock which had
Fig. 82—Bars, channels, beaches, and marsh near Far Rockaway, Long Island, N. Y., as photographed from a height of 7,000 feet at 11 A.M., September 15, 1920. In order from the bottom of the picture upward are: East Rockaway Inlet with a shoal to the left and the sand hook at the end of Long Beach to the right of it; the beach south of Far Rockaway with streets and houses; a group of boats in the inlet at the right of the beach; an area of salt marsh that is filling the lagoon behind the barrier beach; and a small section of the village of Far Rockaway. Scale, about 1:12,000.
escaped attention during very detailed surveys. He states that with proper plates and ray filters the presence of objects invisible to the eye is revealed by the camera.[13] Similar use of air photographs has been made by the English in charting reefs, shallows, and harbors. Thomas says: “In 1917 aeroplane photography was successfully used for charting the harbor of Rahbeg on the Arabian coast.”[14] It is a well-known fact that, under proper conditions, objects submerged to a considerable depth under clear water can be seen from points high above the surface. During the war, submarines were detected and followed by observers in airplanes, and sunken vessels, mines, and other submerged objects have been located by observation from the air. Illustrations in this paper show the possibility of using this method of observation, to some extent at least, in detecting and mapping shoals, channels, and other features under water.
Photographs of channels like those of the Potomac River and its tributaries will be commercially as well as scientifically valuable. The deep-water channel of the Potomac is well known and has been charted; but very little is known of many of the small tributary channels, such as that of Powells Creek (Fig. 75). Where the channels are not well known, such a photograph could be used to advantage in avoiding the shoals, and, by surveyors, first in exploratory work and later as a general guide in charting. Small boats entering this channel could use the photographs either for the original location of the deep channel in case no chart were available or for detecting changes in its course after the chart was made. For uncharted channels, like those of many of the tributaries of the Potomac River, air photography furnishes a quick and accurate means of location.
No amount of sounding, charting, or description could produce so accurate a mental picture of a drowned valley as that produced by Figure 76. In Figures 78 and 79, both of which were taken near Miami, Florida, is illustrated the difference in appearance between natural and artificial channels. The straightaway course and regular outlines of the dredged channel contrast sharply with the winding course and merging outlines of the natural channel. To the student of physiography and earth history the photographs furnish a means of observation of a definiteness heretofore quite unthought-of. On them the actual shape of the channels, submerged terraces, and drowned land forms are shown in detail.
Improvements Under Way Point to Promising Outlook for Airplane Photography
There is, however, need of careful research to determine the conditions under which the best results can be obtained. The height and time of day for exposures with a certain lens, the emulsion and kind of ray filter best suited under certain conditions, the effect of light as it enters and emerges from the water, and the effect of polarization are subjects demanding consideration. Chief among the experiments now under way is the determination of the kind of emulsion and ray filter or color screen that will give the best results. It is a demonstrated fact that, with an emulsion sensitive to red light, objects in the air invisible to the eye because of intervening haze can be photographed through a red filter. It is possible that water can be penetrated in the same way and that filters of other colors will prove advantageous.
Certainly, the air photograph is only in its infancy—but an infancy full of promise. As a means of securing new and advantageous views of subjects of interest, it is not only entertaining but scientifically and commercially valuable. As an aid in mapping it can, even in its present stage of development, serve an important purpose by supplying accurate knowledge of otherwise inaccessible regions, by furnishing details that are valuable but expensive to obtain, and by permitting the frequent and inexpensive revision of existing maps.
INDEX
A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R, S, T, U, V, W, Y.