By James W. Goldthwaite, Ph.D.
INTRODUCTION
This statement seeks to show why a study of erosion and accretion at Hampton Beach is needed. Facts already on record are briefly reviewed; an analysis of the natural processes at work is attempted; and on the basis of these facts and theories suggestions are made regarding the scope and methods of such a study.
THE SITUATION OF HAMPTON BEACH
Hampton Beach lies in the extreme southeast corner of New Hampshire, within two miles of the Massachusetts line. Long, nearly straight beaches stretch both north and south from a central headland, known as Great Boar's Head, where the sea has cut back the end of a glacial drumlin. At the southern end of the south beach, about a mile and half south of Boar's Head, is Hampton Harbor, where tides ebb and flow across the sands, making an unstable entrance to Hampton River and other large tidal creeks that flood and drain several square miles of salt marsh. Salisbury Beach (with its northern end in Seabrook, N. H.) lies on the south side of this entrance or "river," and stretches far down the coast to the mouth of the Merrimac River near Newburyport, Mass. In spite of the rapid development of this coast, in the last fifteen or twenty years, large areas of marsh and some portions of the beach, in Hampton and Seabrook, are only partly occupied and quite unprotected from the sea. The marshlands, especially, are almost as wild and desolate as when they were first seen by Champlain and Capt. John Smith, more than three centuries ago. The situation of this district within easy reach of thickly populated cities, however, and its unique attractions in midsummer make it obvious that the recent rapid growth of Hampton as a recreational center is only the small beginning of a fuller and more elaborate development.
DAMAGE FROM STORMS
The beach is fully exposed to "northeasters" and "southeasters" that sweep up the coast, especially during late fall, winter and spring. Rapid and great changes have taken place during historic time, as indicated more in detail on a later page. These changes did not attract much attention however until recently, when increased use of the shore and investment of money in property subject to destruction by the sea made the matter something of more than idle interest and emphasized the need for resisting further attacks by building artificial defenses.
Beginning about 1909, over $100,000 was spent by the town in the construction of piling and concrete breakwaters, of which only ruined fragments remain today. Because of faulty design or location or incomplete condition when struck by heavy storms, these breakwaters have not prevented nor even seriously delayed the campaign of erosion which the sea has carried on here since 1912. Several blocks of shore lots and streets and about 100 cottages have already been swept away and more are threatened during every big storm.
IMPORTANCE OF A STUDY OF THE PROBLEM
(New Hampshire possesses only about fifteen miles of seacoast. Most of it is already so largely in private hands that a state reservation anywhere else on the shore would be expensive and difficult to arrange. Beach and marshland at Hampton afford the one single opportunity for future development of a shore resort where public rights may be kept dominant and a little unspoiled natural scenery and wild life characteristic of the seacoast may be preserved for future generations.) The enlarging of the district as a recreational center and the accompanying commercial development or "improvement" of the salt marshes call for extensive planning, far-sighted vision, and restraint toward schemes that go no farther than cash profits for interested parties or immediate returns on investment. To secure natural rights for the public, there are bound to be business interests to restrain or resist, as well as sea and storms. Whatever is done to safeguard the spot from attack by the sea, on the one hand, or from capture by private interests on the other, must be done on a large scale and in a well organized way. A recognition of these principles seems to lie back of the establishment of a permanent commission, in New Hampshire, to plan and regulate the development of this shore.
It is believed that the best basis for effective development of Hampton Beach is a study of the problem of erosion, by competent engineers. From such a study we should learn the most effective location and best design for defensive structures, like breakwaters or groynes, and so avoid repeating the costly experiments that have heretofore marked this battle with the sea. If nature is allowed to sweep the sands up and down the coast, to tear out here and fill in there, as storms dictate, and to shift the mouth of Hampton River back and forth after the manner shown in Figure 2, [Map filed with Chief Engineer, War Department, Washington, D. C.] not much can or will be done to improve land or property in the district tributary to the Beach. So it is proposed that a scientific study of erosion and accretion at Hampton Beach be carried out by engineers designated by the National Board for the study of coast erosion, as the first step in securing this important area on the New Hampshire coast to public use.
NATURAL FORCES AT WORK ON HAMPTON BEACH
A glance at the outline maps in Figure 2 and Figure 3 will indicate the fact that erosion and accretion near the mouth of Hampton River have been complex and serious. But before running through the details of these changes, it may clarify the problem to name and briefly discuss the function of the several shore agencies that are known to shift beach material.
Storm waves sweep sand up the beach in a general on-shore direction, but usually diagonally rather than straight, since storm winds come oftener from northeast or southeast than straight toward the shore. Near Boar's Head on both the North and the South Beaches some pebbles attached to kelp are dragged up and cast ashore; but sand makes up the bulk of the beach drift. While there may be shoals off the beach, where glacial deposits lie within reach of the waves, it appears likely that this sand comes from the scour of the fore slope of the beach itself, as the sea slowly beats it inland. Undertow tends to carry the sand back down the beach to deep water. The backwash of breakers on the beach feeds this outgoing bottom current, which moves seaward for a considerable distance through shallow water but loses strength by diffusion as it goes. During storms, when wave action is strengthened and accompanied by strong incoming surface currents, the compensating undertow, which returns this water, is likewise strengthened so that it may be able to roll pebbles down the foreslope of the beach to low tide mark. So there is an endless movement of beach materials up and down the slope, with constant wear and tear on sandgrains and pebbles. As the sediment is thus ground finer and finer it may be spread in flatter and flatter form or even float away, so that the beach slowly loses ground unless the depletion from friction is offset by fresh supplies of sand brought ashore by waves. At Hampton the net result seems to be very slow retrogression of the beach, due to slightly greater losses than gains; but changes are so slight in amount and so irregular that they are difficult to summarize.
Long-shore currents are set up by diagonal waves. Storms usually drive the breakers ashore at an angle. Northeasters and southeasters are both common; but their frequency, intensity and duration follow no set rule, and the wind may blow from almost any easterly quarter during the climax of the storm. From hour to hour both direction and strength of wind may change. Consequently, shore currents may travel northward or southward, here, at any given time, and will vary greatly in vigor. The course which they take and the velocities they have may be influenced considerably, also, by shoals or ledges that interrupt or deflect them. Several ledges, singly and in small groups, in close proximity to Hampton Beach, especially near the mouth of Hampton River, must function thus to modify the action of shore currents. But we have no observational data on which to base a detailed statement of the part they play.
Tidal currents are not probably important at most points on this coast, but they are strong enough at the entrance of Hampton River to appear to be a factor of no little consequence. A considerable prism of water ebbs and flows across the sandy shoals that occupy the space between Hampton and Salisbury beaches, especially when a severe storm coincides with a high run of tides. Enough water passes into Hampton Harbor and up its tributary creeks to overspread several miles of marshland; and currents created by it are probably strong enough to move sands in and out. When, in a storm the tides, waves and shore currents battle for supremacy, on the wide shoals of sand at Hampton River entrance, the precise balance of forces, and its record in the changed configuration of beaches is likely to be somewhat different from that of any previous case.
CONCENTRATION OF THE ATTACKING FORCES ON HAMPTON RIVER ENTRANCE
Where four such agencies as these, each one a variable, conspire to bring about alterations of the shore, the results are bound to be complex and sometimes surprising. No two storms have just the same results at a given place. Also, northeasters and southeasters of different intensities come at irregular intervals and leave records of every variety. Inevitably the strongest effects will be found near the entrance of Hampton River, as already indicated, because there the tides enter into the equation of forces, and the wide deposits of sand lie insecurely anchored in relatively deep water, ready to move in or out or up or down the shore. The varying outlines shown in the maps in Figure 2 illustrate this; but we need much more detailed maps and measurements than these to really understand the operation of the combined agencies.
Other points on the New Hampshire coast, including these portions of the North and South Beaches that lie near Boar's Head are relatively safe from attack. They are tied fast to the great hill of hard boulder clay, and rather closely underlain by firm ground or buttressed by ledges that outcrop through the beach. Though the chief natural supply of sand and stones for these beaches has been cut off by the building of a masonry wall all around the base of the cliffed headland, there is perhaps some material washed up from shoals of glacial drift on which the beach rests. In the course of a century or so, the slow wearing away of the foreslope of Hampton Beach may bring a measurable retrogression of the beach crest; but no sudden or violent change is to be expected. Control by breakwaters or other protective devices is relatively easy there. Northeasters have to round Boar's Head to attack the South Beach and southeasters have to round it to attack the North Beach. But the White Island-Hampton River district lies so far south of the head-land as to be beyond its protective influence. Storms from both quarters hit this shore hard. The ledges have no mantle of glacial soil for waves to gather and convert to beach drift; they are clean hard bosses of rock that rise rather steeply through the sand and are nearly awash at high tide. Although the beach seems almost to be fastened to certain ledges today, experience of the past shows that the position is anything but fixed and permanent. A given ledge that is on Hampton Beach this year may be in the middle of Hampton River a few years hence, and over on Salisbury beach a little later. (Even though no such great change comes for a half century, there is no guarantee that it will not come quickly, any time, when the forces are so combined and directed as to make an assault more effective than the ordinary one. There is no such thing as steady progress here; and there are no regular cycles of change.)
CHANGES WITHIN HISTORIC TIME
The three outline maps of Hampton River entrance (Figure 2) illustrate the variety of changes which take place in rather short spaces of time. These maps are based upon actual surveys at various dates since 1855 by the U. S. Coast & Geodetic Survey and recently by the N. H. Highway Department.
The condition shown in 1855 seems to have remained without marked change for thirty or forty years; for the Newburyport Quadrangle, issued by the U. S. Geological Survey in 1889 (see Figure 1) agrees pretty well with it. However, it is not at all impossible that there were many changes, not recorded, between the two dates when these similar outlines were mapped. From 1908 to 1912, we know from detailed surveys, rapid accretion was taking place at the south end of Hampton Beach, whereby its outer boundary advanced seaward 1000 feet and southward an equal distance to Town Rocks; and continued 1500 feet more so as to tie on to Beckman's Ledges, forcing the river southward across what had previously been the north end of Salisbury Beach. That beach, at the same time, had been cut back some 1200 to 1500 feet. Thus Hampton had gained some 50 acres of beach land and Salisbury had lost about the same amount. It may be that the change was due to heavy northeast storms coming with a strong outgoing tide, so that the sand swept southward along Hampton Beach was dropped off the mouth of Hampton River and spread forward from it, while tidal and shore currents on the other side of the entrance ate away the front of Seabrook Beach. But that is theory. If there were eye witnesses whose observations could be trusted now, they have not been found or consulted; and no attempt has been made to get light on the question from records of the weather bureau during the period of rapid change.
The climax of this growth came in 1912. Development of house lots and construction of streets, sidewalks and a sewer system quickly followed, in the new " White Island" section of Hampton. But within a few years storms had commenced to cut away the beach and undermine the houses. Erosion was fast and furious at times, in spite of efforts to build an effective breakwater, first with concrete and then with piling. Erosion still continues, with real damage during each heavy storm. Approximately 100 cottages have gone and the present crest of the beach lies 5 or 6 blocks back of its 1912 position (Figure 3). Town Rocks, formerly on the outer edge of the White Island tract at high tide mark, now stand far out at low tide and are beaten heavily by waves and currents when the tide is up. As Hampton Beach released its hold on Beckman's Ledges, Seabrook-Salisbury Beach grew forward, so that it now connects with Beckman's, much as it did in 1855. Should the present changes continue, Seabrook Beach may reach farther out and tie on to Town Rocks, while Hampton River entrance shifts through tidal scour to a position between Town Rocks and Hampton Beach. But this forecast is no more likely than one of opposite result. It is impossible to tell which way the next move will be.
Records and maps of earlier dates than 1855 might throw some light on the frequency and extent of such changes as those just reviewed; but search thus far has failed to bring to light much that is of consequence. There was little detailed mapping of the seaboard, in Hampton and Seabrook, since it was scarcely occupied before 1855, and property there was of little value. In view of the early history of this place, however, it seems well to mention one detail—the ledge long known as Bound Rock. In 1640 Capt. Shapleigh, surveyor, ran the line between the townships of Hampton and Colchester (later Salisbury) for the colony of Massachusetts, starting at the mouth of Hampton River. It appears that the line began at a ledge in the middle of the river; for 17 years later, when Shapleigh's line was rerun, this ledge, called Bound Rock, was marked with date and initial letters, as described on the accompanying sheet (Figure 4). According to the Newburyport Quadrangle (Figure 1) the ledge was still in the 1640 position in 1888, though there may have been many changes of the beach in the two centuries and a half between these dates. In 1850, the date (1850) and initials HB and SH were added to the original inscription, and that was somewhat marred rather than improved by recutting. The ledge now lies completely buried by sand, in Seabrook Beach, a few hundred feet south from Beckman's. It is probable that the old inscription on it is the second oldest on the continent, since the oldest known is the Endicott Rock at Weirs, N. H., with the date 1652. It seems that a mark of such antiquity ought to be carefully exposed to view and protected from future loss or defacement.
SUGGESTIONS AS TO THE SCOPE OF THE STUDY
A problem as difficult as this one should of course be approached in a strictly scientific spirit, without prejudice; and ways and means for solving it should be worked out by engineers acquainted with such matters. The facts we have offered, however, suggest a few general observations. The cast of Hampton Beach is more complex than those at many other places on the Atlantic coast. (Long stretches of shore on Cape Cod or New Jersey, for example, are suffering as badly from erosion as is Hampton; but the process is relatively steady, progressive, and free from temporary reversal because the geological agencies there act with greater frequency and almost always in the same direction and without very great changes in strength. This applies particularly to the operation of a dominant shore current or tidal current along successive miles of straight shore line. At Hampton, on the contrary, the markedly intermittent character of the forces, the innumerable changes in direction and strength of currents, and the mathematical possibilities of combinations of four variable factors are so many and so unlike that a long and elaborate set of measurements would appear to be needed, to understand the various forms of attack employed by the sea—or at least the extreme forms that we must reckon with.)
Shallow water contouring of the shore, especially on the sandy shoals off the river entrance, and current measurements under all the different conditions of tide, wind and sea seem fundamental to such a study, and they would probably have to be repeated after each significant alteration of the configuration of the beaches. There should be measurements or estimates of the rate of transfer of sand along those paths that seem to mean most in the problem of shore protection. Whether these might be made by direct measurement or indirectly by comparison of outline and gradient of mapped beach areas as shown on successive charts is a question for the engineer to decide.
While these observations and records would probably have to cover more than the immediate vicinity of the river entrance, if they were to fully serve their purpose, the study in its later stages would perhaps be concentrated on conditions just off the present river mouth, where government engineers have expressed the tentative opinion that relief from erosion might be secured by the construction of a substantial breakwater that would reach from the north bank of Hampton River diagonally out to ledges which lie offshore from Town Rocks. In any case, as the problem now looks—without having the benefit, yet, of a detailed field study—the cure for erosion at Hampton Beach is to be found in the stabilization of the mouth of Hampton River. Here, pretty surely, is the weakest spot. And here also is the key to any future development that would involve harborage and landings for excursion steamers and pleasure craft, and motor boat service for holiday and Sunday crowds arriving by rail at points inland. Once Hampton Beach is fixed, and the river held in position, the full use of its strategic situation will be realized.
APPENDIX
Appended hereto are the markings on "Bound Rock" copied by Mr. French of South Hampton, N. H., with descriptions of the same.
"Bound Rock " is as big as my barn, perhaps. On the southerly side of it the water came up to the ledge like a wharf. On top, here, much like a school desk is the marking
AD
1657
Below this is what was for a cross and crown, perhaps, but now (several years ago) worn by the elements so as to be hardly seen.
On it was also for
H B
1850
For Hampton Bound, to show their southern limit of course. We were told this was made after the ledge was uncovered.
Also
S.H.
This was to show the limits of our (South Hampton's) possession, as I understand it. The old marks on the stone were apparently recut, but with tools and workmen not used to the job, so the old letters and figures were hurt rather than improved."
Description of the marks on Bound Rock furnished by Frederick B. French, Amesbury, Mass., RFD 1, octogenarian. selectman, surveyor of South Hampton.