Results of analyzing several areas of marsh are given in Table 1. Note 

 that drainage density in most cases is more than 10 kilometers per square 

 kilometer and ranges up to 50 or more. This maybe compared to so-called 

 fine -textured terrestrial drainages which have densities of around one kilometer 

 per square kilometer. , 



Along the edges of creeks, marsh grass is more lush than in the level 

 areas away from the creeks. This '.'edge marsh" extends from the creekside 

 edge of the marsh grass to the top of the levee and has an average width of 

 8.6 meters. In the headward portions about 70 percent of the vegetated area 

 is "edge marsh" while the downstream portions are composed of about 15 per- 

 cent "edge marsh". Taken as a whole it is estimated that the entire drainage 

 systems are composed of about 50 percent "edge marsh". 



When the directions of the segments of the creeks in a drainage system- 

 are not randomly distributed but are systematically oriented in a particular 

 direction, this method yields biased results. However, by rotating a grid and 

 taking the mean number of intersections for various angles of the grid this 

 effect is eliminated. In addition, by plotting the number of intersections ob- 

 tained against the angle of the grid, the mean direction of the orientation of the 

 drainage system can be accurately determined. The number of intersections 

 is minimal when the grid is parallel to the mean direction of orientation. 



Analyses of salt marsh drainages have shown that most of them lack 

 directional orientation. This is in line with the idea that there is little or no 

 structural control involved and that dynamic factors are dominant in develop- 

 ment of these drainages. 



D, - Future development 



Eventually, if sea level remained constant and coastal subsidence did not 

 occur, one would expect the region of mature vertical development of the marsh 

 to progress headward until the entire marsh is at or near the level of high water. 

 As this occurred the drainage would be automatically deprived of its runoff and 

 would be gradually destroyed by sedimentation. It follows, then, that these 

 elaborate and fast growing drainages are characteristic of an immature marsh 

 which is being maintained in the growing stage either by rising sea level or 

 subsidence of the land or both. 



Reference s 



Horton, R. E, 1945 



Erosional development of streams and their drainage basins; hydrophysical 



approach to quantitative morphology. 



Bull. Geol. Soc. Am., 56^: 275-370. 



1) Aided by grant from National Science Foundation. 



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