waters such as those of some estuaries in the southeastern United 

 States. 



II. SITE REQUIREMENTS 



1 . Elevation . 



Elevation and the tidal regime determine the degree, duration, 

 and timing of submergence. These, in turn, largely determine the 

 location and type of marsh. However, there does not appear to be a 

 simple relationship for submersion, marsh location, and development. 

 For example, low marsh may occur (a) under regular diurnal tide 

 cycles, two lows and two highs approximately equal in magnitude 

 daily, typical of much of the Atlantic coast; (b) where water level 

 is largely controlled by wind setup, and tides may remain high or 

 low for days at a time; and (c) under mixed semidiurnal cycles of 

 two different highs and two different lows, daily, as in San Francisco 

 Bay, plus numerous variations of these. Thus, the controlling factor 

 from the standpoint of water levels may be the average daily submer- 

 gence period, the longest period of continuous submergence, certain 

 wind- induced, extended periods of submergence or exposure, or some 

 combination of these. Consequently, the best estimates of suitable 

 elevations for marsh building at any given site are obtained by ob- 

 serving nearby natural marsh. Lacking this, trial plantings extending 

 between points well above and well below the estimated final eleva- 

 tions should be made and the survival determined. Where planting on 

 large, relatively flat areas, trial plantings are needed to establish 

 the suitable planting elevations. The lower limit is usually well de- 

 fined. On smaller plantings, allowances are made by overlapping the 

 most probable adaptation limits. Estimated adaptation limits are pre- 

 sented by species in the planting techniques. Section IV, 3. 



2. Slope . 



Slope determines the area suitable for marsh growth. Productive 

 marshes are found over a very wide range of slopes; however, either 

 an excessive or an insufficient slope can have important effects on 

 marsh establishment and growth. Steep slopes facilitate drainage and 

 aeration but are more difficult to plant, more resistant to natural 

 colonization by marsh species, and limit the area that can support 

 marsh. In addition, waves dissipate their energy over a short distance 

 when meeting on abrupt shoreline. On a gradual -sloping shoreline, wave 

 energy will dissipate over a longer distance. Very gradual slopes im- 

 pede circulation and drainage and are usually less productive due to 

 bare salt slicks or pannes and large areas of stunted plant growth. 

 Much of the so-called short form of smooth, cordgrass occupies essen- 

 tially flat areas. On filled or graded slopes, uneven settling 



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