• Quite often it is possible to divert 

 sufficient water from larger streams 

 and rivers to maintain small lakes 

 and ponds. Extensive fresh-water 

 areas have been created on some 

 marshes by constructing dikes (fig. 

 17). Some elaborate concrete 

 water-control structures and spill- 

 ways may be necessary, but often 

 earthen and rock dams will suffice — 

 the excess water simply flows over 

 the top. 



Water-control structures should 

 be designed so that water levels can 

 be raised or lowered as the need 

 arises. A temporary "draw-down" 

 of the water to expose the soil dur- 

 ing the first half of the growing 

 season is one of the most effective 

 methods of obtaining germination 

 of the seeds of cattail and bulrushes 

 and the establishment of the seed- 

 lings. The exposed soil should be 

 kept moist and not permitted to dry 

 out. Ponds are a conspicuous fea- 

 ture of coastal marshes and valuable 

 in varying degrees to waterfowl, 

 fur animals, and other wildlife. A 

 good marsh is one having a ratio of 

 about 80 percent vegetation to 20 

 percent open water. 



On a tidewater marsh, the differ- 

 ence of a few inches in water levels 

 has a marked influence on the plants 

 and animals found there. Their 

 natural distribution is governed by 

 their ability to withstand varying 

 degrees of intermittent and pro- 

 longed submergence and by their 

 tolerance to different concentrations 

 of salts or chlorides. 



Brackish marshes extend along 

 the Atlantic coast and the Gulf of 

 Mexico — the result of the mixing of 

 the salt waters from the sea and the 



• ■^e^raHp^lRw^PgSBP''**'' 



Figure 17. — Using a dragline to construct 

 a dike with an impervious core of 

 marl. 



fresh waters coming down to the 

 coast from the interior. Prolonged 

 droughts and high temperatures in- 

 crease salinity of the water in these 

 marshes. Often not much can be 

 done to correct such a situation, but 

 all sources of fresh water such as 

 runoff from woods, fields, and 

 drainage ditches should be used. 

 Unfavorable water conditions on a 

 marsh can frequently be improved 

 by diverting water from a nearby 

 stream, or by a small amount of 

 judicious diking, coupled with the 

 use of deep wells, either free-flow- 

 ing or pumped (fig. 18). In some 

 instances dynamite-blasting of a 

 series of small ponds and connect- 

 ing ditches across a high, "tight" i 

 marsh encourages its use by musk- I 

 rats. Care must be taken to avoid 

 lowering ground-water levels that 

 control the gi^owth and distribution 

 of essential food plants. Upper 

 reservoirs or pools may be con- 

 structed to impound water that can 

 be used to stabilize water levels in 

 the lower ponds and ma:rshes. 



Level ditching is practiced exten- 

 sively in the Gulf Coast marshes, 

 not only to help control fluctuations 

 in water levels but also to lessen 

 difficulty of foot travel by trappers. 



12 



