TIDAL DATUM PLANES (5 
TABLE 3.—Half-tide level minus sea level 
Atlantic one t a Foot | Gulf Coast—Continued Foot 
astport, Maine____________ — 0. 08 5 < 0. 10 
Portland, Maine-—————— —0. 02 Sa Sc, ee a onde 
Bostonw Macseege & 2-2) 2 051 od =. 12 7es pull Ns REY Gules raih® 0. 06 
Woods Hole, Mass__._______ 0. 05 palvesvon, Tex Cae ist 
Providence. Fil. so. 2 es 0. 13 Porth Isabel hexsats nt ee (0) 10) 
Neo Onterkued ere Beng Se 0.13 | Pacific Coast: 
New London, Conn__________ — 0. 06 sem, IDWee@, Calitr. 22-2 0. 03 
ING wae VOrkagNe Ven se ee ce =. Os ILE Wolke ye Ceili es ep ae SO 0. 01 
é Sern cliyd te O@les Nate ea se = 0% Onl Los Angeles Harbor, Calif____ 0. 03 
Mi laMbIG -@ibyetINeis. SS Sie —0. 03 Port Hueneme, Calif_________ 0. 03 
IPianilexclalolne, Ie Ss be — 0. 23 Rortieameluises Calta eee 0. 04 
Mewes lise es aereeu rey ky as — 0. 02 Sanwbiranciscos Calin saan 0. 05 
Baltimore, Midas 22 lee.) — 0. 02 StocktonmCahiones 2s sass es —0. 04 
PATA OlISs WG aso oe ee te 0. 02 Crescent City, Calif_.______- 0. 04 
Washmeton, DiCr suse vie aa USO NStoriat: Oneg ames eaem sae ne! 0. 04 
Rerelamond sy Vieas ae ist See == (0) dat INeah i BayawWashaes tse eee es. 0. 04 
INoriolig Vise ate Se. anes cae OO Seautlew Wiaslimeamwrss 1 heme oe 0. 02 
Walmimeton, Ne Co! esi St —0. 06 Friday Harbor, Wash________ 0. 22 
Sombbpont, WIN Cas sus- oan Fe —0:. 04 | Alaska: 
Chasiesignm, 8, Cia. s222 5425 =. 1 I@irolonlleyin se ee ee —0. 01 
Daven nai Gases Soe oo ee == (Q)e tt SUI a Pee eee, emperor RE —0. 09 
Wey ports Mla Weck be) ee —0. 05 Sitka eee sla OT he airs 0. 03 
Daytona Beach, Fla___-_--_- 0. 02 Sikaigawiaiyeaess: (out i aa Eola ee (0) 1 
Miami Dae es aoe ss ete 0, Wu GW itrt sic cra elie call lee 0. 02 
Gulf Coast: a a ait Sweeper Cove, Adak I_______ (0). a0 
Ke Sind eS ee ae WE Tassaer PANU el he ee ee 0. 
Gaal Keys alae Seen eseeee —0. 02 Miansenene [by Boni ane 29 
Rensacola, Blas 522 [Stee 2S *0.01 | Hawaiian Islands: 
Bayouhviguade: Wass 2 Sate be *0. 00 Foro ule oe oy en ae =: 02 
dc SUK Culp patel coe 2 ie Mp1 hee as —0. 02 
Determination of Half-Tide Level 
Since the variations in half-tide level are very nearly the same as those im sea level, 
the procedure employed in determining the plane of mean sea level becomes applicable 
also to the determination of the plane of half-tide level; and, as in the case of mean sea 
level, a determination based on 19 years of tide observations is taken as constituting 
a primary determination of the datum of half-tide level. 
For deriving the datum of half-tide level from a short series of observations the 
direct determination is corrected by means of simultaneous observations at some near- 
by station for which a primary determination is at hand. The procedure is similar in 
all respects to that employed in correcting to a mean value the determinations of sea 
level from short series of observations. As an example, we may derive the datum of 
half-tide level at Annapolis, Md., from two different months of observations, using 
Baltimore, Md. as the primary station. 
At Annapolis half-tide level for February 1947 read 4.04 feet on the staff and for 
June of the same year it read 5.24 feet. At Baltimore for these same months half-tide 
level was, respectively, 3.68 feet and 4.97 feet. For the 19-year period 1930-1948 
half-tide level at Baltimore was 4.35 feet on the staff. Hence, for February 1947 a 
correction of 4.35—3.68=0.67 foot is indicated and for June 4.35—4.97=— 0.62 foot. 
Applying these corrections to the respective half-tide levels at Annapolis the mean 
value for February is 4.04+0.67=4.71 feet and for June, 5.24—0.62=4.62 feet. Thus 
