DRAINAGE OF WET LANDS OF SOUTHERN LOUISIANA.' 21 



Thus on Timbalier Island, directly opposite the mouth of Terrebonne Bayou, 

 the rise, according to the lighthouse keeper, was only 6 feet. At Port Eads, 

 which is practically 12 miles out in the Gulf, and where the water is much 

 deeper, the rise was only 3.4 feet and subsided in a few hours. 



To the westward of this portion of the coast line the tides due to this storm 

 were not nearly so high. This was doubtless due to the difference in the 

 character of the coast line, and to a less intensity and duration of the storm. 

 Concerning this section Mr. Shaw says : 



In the western portion of Terrebonne Parish, the flood height amounted to 

 about 5 feet with a gradual falling off to the west. On the Big Wax and Little 

 Wax Bayous and Bayou Sale, in St. Mary Parish, the maximum floods probably 

 do not exceed 4 feet. 



As mentioned in the general description of this section, the coast line of 

 the western portion is very regular in outline, and immediately along the beach 

 there is an almost continuous ridge of sandy material. The water directly 

 offshore is deeper than that along the eastern coast, at least is deeper than the 

 numerous lakes and bays of the eastern section, and as a result the tides due 

 to wind have never reached the height experienced along the coast of the 

 eastern part. The high tides have never overtopped these ridges, and as the 

 water only poured in through the low places it did not enter in sufficient volume 

 to flood the land deeply before the recession of the tide occurred. By closing 

 these comparatively short gaps in this ridge, complete protection from tidal 

 overflow would be secured for the western section, but some provision would 

 necessarily have to be made for discharging the natural drainage water from 

 the interior. 



From an examination of flgure 1 it would appear that reclamation districts 

 on many portions of tne coast will be compelled to build levees not only to keep 

 out the water of the surrounding swamps, but also to prevent tidal overflow 

 in times of storm. The heights of the tide indicated on this map are the highest 

 that have been experienced since the country has been settled, and should govern 

 the height of levees on districts in the various localities. From a study of the 

 nature of these tropical hurricanes the Weather Bureau forecaster at this point 

 has concluded that there is an area of maximum velocity of wind in these 

 storms that strike the coast, and that at or near where this maximum velocity 

 occurs a much higher tide than the average may be expected. In the storm of 

 September 20, 1909, the area of highest wind velocity struck the coast at or 

 near the mouth of Bayou Terrebonne. As the storm center may strike at any 

 point in future storms we may expect tides over limited areas exceeding those 

 of the above-described storm, but it is unlikely that in general the present 

 records will soon be exceeded. It is probable that these severe storm centers 

 will occur on the Gulf coast with about the same frequency as do the torna- 

 does of the upper Mississippi Valley, and therefore it is suggested that pro- 

 tection from them should be sought in insurance rather than in building levees 

 of sufficient height to prevent overflow from these limited areas of extremely 

 high tide. 



In connection with the problem of protection from tidal overflow, the plan 

 of providing a general protection levee for the whole of the coast line, rather 

 than of constructing individual levees for each district, has been considered by 

 local engineers. The feasibility and cost of such a plan could be determined 

 only after a complete survey of the district had been made, and a comprehensive 

 plan had been carefully worked out. However, there are some general features 

 that can be stated, thus giving an idea of the nature of the problem. The larger 

 the levee district, other things being equal, the less the cost per acre for levee, 

 for the length of levee per unit of area varies as 1 divided by the square 



