The Face of the Earth as Seen from the Air / A Study in the Application of Airplane Photography to Geography

by Willis T. Lee

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.