True... 
it acts as a semi permeable membrane
        
             
        
        
        
Im confused about the question can you explain
 
        
             
        
        
        
Answer: Steep, high velocity, no silting. The high water speed picks up silt from the bottom instead of letting it settle to the bottom. When the land gets level like often happens at the mouth of rivers where the water spreads out and slows down, silt settles to the bottom and you could get a wide, shallow delta.
(Put in own words this is from online hope it helps)