[MCN] Big dead trees help keep a stream together

[Lance Olsen]

 E a r t h   S u r f a c e   P r o c e s s e s  
 a n d   L a n d f o r m s     1 8  
 S e p t e m b e r   2 0 0 7   
 D O I :   1 0 . 1 0 0 2 / e s p . 1 5 9 3 

 C h a r a c t e r i s t i c s ,  
 d i s t r i b u t i o n   a n d  
 g e o m o r p h i c   r o l e  o f   l a r g e  
 w o o d y   d e b r i s   i n   a  
 m o u n t a i n   s t r e a m 
 o f   t h e   C h i l e a n   A n d e s 
 A n d r e a   A n d r e o l i  et al

 K e y w o r d s :   l a r g e   w o o d y  
 d e b r i s ;   c h a n n e l  
 m o r p h o l o g y ;   v a l l e y   j a m s ;  
 l o g - s t e p s ;   A n d e s

 A b s t r a c t 
 T h e   p a p e r   p r e s e n t s   a n  
 a n a l y s i s   o f   a m o u n t s ,  
 c h a r a c t e r i s t i c s   a n d  
 m o r p h o l o g i c a l   i m p a c t   o f 
 l a r g e   w o o d y   d e b r i s   ( L W D )  
 i n   t h e   T r e s   A r r o y o s  
 s t r e a m ,   d r a i n i n g   a n  
 o l d - g r o w t h   f o r e s t e d  
 b a s i n 
 ( 9 
 1   k m 2 )   o f   t h e   C h i l e a n  
 S o u t h e r n   A n d e s .   L a r g e  
 w o o d y   d e b r i s   h a s   b e e n  
 s u r v e y e d   a l o n g   a 
 1 
 5   k m   l o n g   c h a n n e l  
 s e c t i o n   w i t h   a n   a v e r a g e  
 s l o p e   o f   0 
 0 7   a n d   a  
 g e n e r a l   s t e p- p o o l / c a s c a d e 
 m o r p h o l o g y .   S p e c i f i c  
 w o o d   s t o r a g e   i s   v e r y  
 h i g h   ( 6 5 6    7 1 0   m 3  
 h a" 1  ) ,   c o m p a r a b l e   t o  
 t h a t   r e c o r d e d 
 i n   o l d - g r o w t h   f o r e s t e d  
 b a s i n s   i n   t h e   P a c i f i c  
 N o r t h w e s t .   H a l f   o f   t h e  
 L W D   e l e m e n t s   w e r e  
 l o c a t e d 
 o n   t h e   a c t i v e  
 f l o o d p l a i n ,   a n d   a r o u n d  
 t w o - t h i r d s   o f   L W D  
 e l e m e n t s   w e r e   f o u n d   i n  
 a c c u m u l a t i o n s . 
 D i f f e r e n t   t y p e s   o f   l o g  
 j a m   w e r e   o b s e r v e d ,   s o m e  
 h e a v i l y   a l t e r i n g   c h a n n e l  
 m o r p h o l o g y 
 ( l o g - s t e p s   a n d   v a l l e y  
 j a m s ) ,   w h i l e   o t h e r s   j u s t  
 l i n e   t h e   c h a n n e l   e d g e s  
 ( b a n k f u l l   b e n c h   j a m s ) . 
 L o g - s t e p s   r e p r e s e n t  
 a p p r o x i m a t e l y   2 2 %   o f   a l l  
 s t e p s ,   w h e r e a s   t h e  
 e l e v a t i o n   l o s s   d u e   t o  
 L W D 
 ( l o g - s t e p s   a n d   v a l l e y  
 j a m s )   r e s u l t s   i n   2 7 %  
 l o s s   o f   t h e   t o t a l   s t r e a m  
 p o t e n t i a l   e n e r g y .   A b o u t 
 1 6 0 0   m 3   o f   s e d i m e n t   i s  
 s t o r e d   i n   t h e   m a i n  
 c h a n n e l   b e h i n d   L W D  
 s t r u c t u r e s ,  
 c o r r e s p o n d i n g   t o 
 a p p r o x i m a t e l y   1 5 0 %   o f  
 t h e   a n n u a l   s e d i m e n t  
 y i e l d .

-- 
  =============================================================
  "The outlines of the carbon cycle, in organisms 
at any rate, have been evident since Joseph 
Priestley's day. The critical step, 'obviously', 
is the photosynthetic reduction of carbon 
dioxide."

"What can be said with assurance is that there is 
a unique and nearly ubiquitous compound, with the 
empirical formula 
H(2960)O(1480)C(1480)N(16)P(1.8)S called living 
matter. Its synthesis, on an oxidized and 
uncarboxylated earth, is the most intricate feat 
of chemical engineering ever performed - and the 
most delicate operation that people have ever 
tampered with."

Edward S. Deevey, Jr. Mineral Cycles.
Scientific American, September 1970
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