A Soil Bioengineering Guide - Chapter1 - Making the Connection - Watersheds

8/13/2019 A Soil Bioengineering Guide - Chapter1 - Making the Connection - Watersheds

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CHAPTER 1Ma kin g th e Con n ect ion Watersheds

We all w ant healthy w atersheds, open space, and diversity in our plant s and animals. As we begin

to restore our r ipar ian forests and repair st reambanks w e must look at a broader pictu re.We must

understand what is happening upstream of us and be aware of how our actions affect those dow nstream

Bruce Babbit, th en-Secretary of the Int eri or. (W illi ams and others 1997)We must understand the links

betw een upl and and r ipar ian ecosystems.We must also understand w hat mak es these forests healt hy,

w hat their fu nctional and str uctu ral characteristics are, and how they behave when they are functioning

properl y, in concert , as a w atershed.


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We a ll w a n t h e a l th y w a t e rs h e d s , o p e n s p a c e, a n d

d i vers i t y in our p l an t s a nd a n i ma l s .As w e beg in to res tore

our r ipar i an fores t s and repa ir s t ream ban ks we m ust l ook

a t a b ro a d e r p ic t u re . We m u s t u n d e r s t a n d w h a t i s

h a p p e n i n g u ps t r ea m o f u s a n d b e a w a r e o f h o w o u r

a c t i on s a f f e ct t h o s e d o w n s t r ea m B ru c e B a b b it , t h e n -

Secretary of t he Inter ior. (Will iam s a nd oth ers 1997) We

mu st unders t an d the li nks be tween upl and a nd r i par ian

e c o sy s t e m s . We m u s t a ls o u n d e r s t a n d w h a t m a k es t h e s e

fores t s hea l thy , w ha t the ir func t i ona l and s t ruc tura l

c h a r a c t er is t ic s a r e , a n d h o w t h e y b e h a v e w h e n t h e y a r e

func t i on i ng properl y, i n concer t , as a w a te r shed .

. . . P ro fessor Noe l Hynes o f th e Uni vers i t y o f Water l oo

i n Onta r io wa s am ong the fi r s t t o descr ibe how l i nks

be tween th e so il an d veget a t i on i n a wa te r shed combi ne

w i th l oca l c l im ate to produce the phys i ca l s t ruc ture an d

biological product ivi ty of s t ream s. (Hynes 1975) (Ibid .)

A SOIL BIOENGINEERING GUIDE

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Mountains to delta watershed

Hynes syn thes i s , the synergy be tween a r i ver and i t s

w a t e r s h e d , h a s b e en d e s c r ib e d in v a r i o u s w a y s . At fi r s t ,

the r i ver-w ate r shed re l a t i on w as v i ewed a l ong the

l ong itud i na l g r ad i en t o f a r iver f rom i t s headw ate r s t o

the ocea n (cal led the r iver cont inuum concept) . (Ibid .)

More recent l y, researchers , na tura l is t s , sc ien t i s t s , an d

oth er eco-explorers ha ve begun to view the relat ions hip

of ri vers from ups t ream to dow nst ream , f rom ups l ope to

d o w n s lo p e , a n d f ro m c a n o p y t o s u b s u r f a c e. Th e y a r e

l ooki ng for c lues to be t t e r unders t a nd the l inks a mo ng

a l l o f t h e n a t u r a l s y s t em s t h a t m a k e u p t h e w a t e rs h e d

environm ent . Ward (1989) descr ibes this m ul t id imen siona l

c o n c ep t i n f o u r d im e n s i o n s a n d m a k e s a l a n d s c a p e c o n -

nec t i on for each : long i tud i na l (ups t ream to dow nst ream ),

l a t e r a l (flo odpl a i ns to upl ands) , ver t ic a l (subsur face to

r ipar i an can opy), an d t em pora l (because the o ther three

dim ension s are dyna m ic over t ime). (Ibid .)


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MAKING THE CONNECTION WATERSHEDS

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This cha pter not on ly provides a h ol ist ic view of how

h e a l t h y w a t e r s h e d s f u n c t io n , b u t i t b u ild s a f o u n d a t i o n

f o r u n d e rs t a n d i n g w h y t h e l in k s b e t w e e n u p l a n d a n d

r ipar i an an d aq ua t i c ecosys tem s are v it a l l y i mpor t an t . I t

h e l ps u s t o u n d e rs t a n d t h e im p a c t s o f a d a m a g e d w a t e r-

s h e d a n d w h y s t re a m b a n k s f a il . I t e x pl a in s w h y w e m u s t

l ook ups t ream an d exam i ne the ac t i v it i es o f the en t i re

w ate r shed be fore any s t ream ban k s t ab il iza t i on or w a te r -

shed res tora t i on w ork beg i ns .Without th e w a te r shed-sca l e

perspect i ve, the r isk o f undes i r ab le e f fec t s d ram at i ca l ly

i nc reases .

Origin and PurposeWa t e r s h e d s , a s w e kn o w t h e m t o d a y , a r e co m p l e x

ecosys tems com posed o f d i f fe rent lan d t ypes r ang i ng

f rom dry d eser t lan dscapes to r ich l y fores ted areas . These

l and t ypes a re connec ted by equa l ly compl ex d ra i nage

ne tw orks o f r iver s an d s t ream s.

A w ate r shed s t opographi c shape , som et im es refe r red to

as a ba s i n , w as formed by t ec ton ics and g l ac ie r ac t i v it y

m ore than 4 b il li on year s ago . Natura l e ros ion deve l oped a

compl ex d ra i nage n e tw ork .As the Ear th s sur face reached

i t s sa tura t i on l eve l dur ing i n tense r a i n fa l l , w a te r m oved

across th e sur face to form r i ll s and gu l li es .

G ul li es w ere inc i sed to w i der and l a rger chan ne l s ,

eventua l ly becomi ng r ivers an d s t ream s. Sma l le r s t ream s

are ca l led fi r s t an d second order s t reams w hi le l a rger

s t ream s a nd r ivers a re th i rd order and h i gher. Thi s

sophi s t i ca ted ne tw ork o f s t reams se t s up an e l abora tea n d u n i q u e p lu m b i n g s y s t em t h a t a l lo w s w a t e r s h e d s t o

col lec t d i scha rge an d t r anspor t both runof f a nd sed i men t

t h r o u gh t h e s y s t e m t o l a k e s a n d o c e a n s .

Sediment and RunoffQuant i t i es o f d i scha rge an d sed i ment a re impor t a n t

because an i mba l ance in e i ther a f fec t s the dyna mi cs

o f t h e s tr ea m a n d , u lt im a t e ly, t h e s t re a m b a n k s . M os t

w ate r sheds rece ive th e ir d i scharge f rom preci p it a t i on ,

i nc lud i ng mel t i ng snow a nd subsur face d i scharge .When

the i nfi l t ra t i on ca pac i t y o f the so i l is exceeded , shee t l ike

fl o w c a l le d s h e et w a s h o c cu r s . S h e et w a s h p i ck s u p

ve loc it y an d i nc reases i n depth a s i t flow s . Eros ion o f

sed i ment occurs wh en the shea r s t ress o f the wa te r is

su ffi c ien t t o t r an spor t sed i ment . Thi s shee t l ike flow

cond i t i on i s o f t en re fe r red to a s Hor ton over lan d fl ow .

Hor ton overl and fl ow causes th e h i ghes t r a t es o f h i ll s lope

erosion. (Mount 1995)

I t is na tura l for banks to e rode , i t is i n tegra l t o s t ream

sys tem s. The l oca t i ons and r a tes o f e ros i on are the ma i n

c o n c er n . C h a n g e s i n fl o w d i re c ti on a n d s e d i m e n t r a t e s

can h as ten e ros i on . These chan ges can o f t en be t raced to

human ac t i v i t i e s .

P r im ar i ly , there a re three way s for s t reamba nks to e rode :

1.Hydraulic.Wat er carr ies aw ay bed a nd /or ban k

m ater i a l because the shear s t ress o f the fl ow i ng wa te r is

s t ronger than t he shea r s t reng th or cohes i veness o f the

ban k. (Fischenich 1989) Hydra ul ic fa i lure i s usua l ly

charac te r i zed by a l ack o f vege t a t i on , h i gh bounda ry

ve loc it i e s [sw i f t h i gh wa te r ], an d no ma ss wa s t i ng a t the

toe of t he ban k. (King 1993) This gen eral ly occurs in

non cohes ive soi ls ; g lac ial t i ll is a good exa m ple.

2.Geotechnical. G ravit y exer t s a s t ronger force on the

b a n k t h a n t h e m a t e r ia l s ca n w it h s t a n d , a n d t h e y sl id e .It s s h e a r s t r e n g t h i s c o m p ro m i s e d . In m a n y c a s e s , e x ce s s

m oi s ture re ten t i on is the cause o f ma ss w as t i ng

(l ands l i de) a t the toe o f the ban k .

3.Hydraulic and Geotechnical. Bank fa i lure caused by th i s

combi na t i on i s more l ike ly to occur tha n e i ther one a l one .

Examples include:

Bed degrada t i on and e ros ion , w hi ch lowers the bed so

mu ch tha t the banks become overl y s t eep and f a i l

(slide).

Mass w as ted m ater i a l ly i ng a t the toe o f a s l ope is

w a sh ed a w ay. (Fischen ich 1989) (King 1993)

The i nfi l t r a t i on capa c it y o f var i ous wa te r sheds can va ry

w i de ly a ccord i ng to th e s t ruc tura l charac te r is t i c s and

m akeup of the w a te r shed . (S t ream Cor r idor Res tora t i on

of fe r s more de t a i led i n format i on on t h i s t op ic . See the

Bibliography for th e com plete reference.) Wat ershed s th at

a re heavi ly fores ted w i th a r an ge o f veget a t i on t ypes

genera l ly have h i gh i nfi l t ra t i on capa c it i e s .Trees , b rush ,

an d g rasses i n te rcept and d i ss ipa te th e energy f rom

ra i ndrops . Ra i ndrops tha t reach the g round uni mpeded

can d i s lodge so i ls a nd cause e ros i on . The presence o f l ush

vege t a t i on is genera l ly assoc i a ted w i th an a bunda nce o f

organi c ma ter ia l s above and be low the sur face an d h i gh l y

deve loped root sys t ems tha t keep the so i l s t ruc ture porous

an d w e l l d r a i ned . Wi th sur face an d subsur face cond i t ions

l ike these , r ap i d infi l t ra t i on ca uses a s i gn i fica nt por t i on o f

the prec ip i t a t i on to end up a s g round w ate r .The g round

w ater i s l a t e r re l eased as s ubsur face d i scharge in to l akes ,

r iv e rs , a n d s t re a m s .


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Conversel y, the i nfi l t ra t i on capa c it y i s re l a t i ve ly l ow for

w ate r sheds th a t a re covered sparse ly w i th vege t a t i on .

Their soi l s t ructure i s poorly developed a nd poorly

dra i ned . For exam pl e, deser t so il s a re genera l l y non-

porous an d very suscept ib le to over lan d fl ow cond i t i ons .

Fa r m i n g , m i n i n g , lo g g in g , g ra z i n g , b u il d in g a n d r o a d

cons t ruc t i on , an d rec rea t i on a c t iv i t ie s ma y l eave bare

ground w i th noth i ng to i n te rcept ra i n fa l l . Consequen t l y,

such a c t iv i t ie s ha ve the poten t i a l t o s i gn i ficant l y d i s turb

the ecological integr ity (fun ct ion an d st ructu re) of the

w a t e r s h e d .


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What benefi c ia l uses depend on a qua t i c resources

occur ri ng in th e w a te r shed? Whi ch w a te r q ua l i t y

param eters a re c r it i ca l t o th ese uses?

What i s the re la t i ve abunda nce an d d i s t r ibu t i on o f

spec ies o f concern tha t a re im por t an t i n the w a te r shed

(e .g. , threa tened or endan gered spec i es , spec ia l s t a tu s

spec ies , spec ies emph as i zed i n o th er p lan s)? Wha t i s the

d i s t r ibu t i on an d cha rac te r o f the ir hab i t a t s?

What cur rent an d pa s t hum an uses (e .g . , Fores t Serv i ce

ma na gemen t prac t ices and pr i va te a nd pub l ic use

p a t t e rn s ), o n a n d a d j a c e n t t o f or es t la n d , m a y b e

a f fec t i ng the w a te r shed?

Healthy W atershedsWi th w h a t w e kn o w a b o u t w a t e rs h e d s a n d w h a t d i s t u rb s

them , l et us b ri efly cons i der som e benefi t s o f hea l thy

w a t e r s h e d s . H e a l t hy e c os y s t e m s [a n d w a t e rs h e d s ] a r eres il ien t an d recover rap i d l y f rom na tura l and h um an

d i s turbance . Cos t an za (1992) defi ned a hea l thy ecosys tem

a s o n e t h a t is s t a b l e a n d s u s t a i n a b le i n t h a t i t m a i n t a i n s

i t s organ i za t i on an d a u tonom y over t im e an d i s res i li en t

to s t ress . High b i o l og ica l d i vers i t y an d h ab i t a t compl exit y

provide m uch of the res is t an ce an d res il ience exhi b i t ed

by hea l thy w a te r sheds . (Wi ll iam s a nd o thers 1997)

Hea l thy w a te r sheds exhi b it a h i gh degree o f connec t iv i t y

f ro m h e a d w a t e rs t o d o w n s t r e a m r e a c h e s, f ro m s t r e a m s

t o fl o o d p la i n s , a n d f ro m s u b s u rf a c e t o s u r f a c e . F lo o d s

can spread onto fl oodpl a i ns , w here the ir energ ies a red i ss ipa ted a nd s i l t f rom fl oodw ater s i nc reases so i l

produc t iv i t y. High conn ec t iv i t y a l so enab l es fish an d

w i ld l ife popul a t i ons to m ove f ree ly th roughout th e

w ate r shed , w hi ch inc reases the i r v iab i li t y and f a c il it a t es

t r ans fe r o f nu t r ien t s f rom r i ch dow nst ream reaches to

less-product ive hea dw at ers . (Ibid .)

Ecological IntegrityWi thout a w a te r shed-sca l e perspec t ive an d a c lear

u n d e r s t a n d i n g o f t h e d o m i n a n t p h y s i c a l, b io lo g ic a l , a n d

hum an processes tha t regula te w a te r shed ecosys tem

func t i ons , there i s cons i derab le r i sk o f un des i rab l e s i de

e f fec t s from res tora t i on a t t em pts an d the a ppl ica t i on o f

s t ream ban k and l akeshore s t ab il iza t i on t echni qu es . Wi th

a g rea te r unders t and i ng o f s t ruc ture an d func t i on a t the

w a t e r s h e d s c a le , t h e c o n s e q u e n c e s o f r es t o ra t i o n a n d

s t ab i li za t i on a c t iv i t ie s becom e m uch more pred ic t ab l e.

A w ate r shed a na l ys is shoul d precede an y s t ab i l iza t i on

w ork . (See append i x A for a m ore compl e te d i scuss i on

of a w a te r shed a na l ys is an d i t s benefi t s . ) The an a l ys i s

s h o u l d , a t a m i n i m u m , a d d r e s s t h e fu n c t io n a l a n d

s t ruc tura l charac te r i s t ic s o f the wa te r shed an d genera te

a n s w e r s t o s u c h b a s i c q u e s t io n s a s :

What e ros ion processes a re dom i nant w i th i n the w a te r-

shed (e .g . , sur face e ros ion processes or m ass w as t i ng)?Where have th ey occurred or are th ey l ikely to occur?

What a re th e dom i nant hydrol og ic cha rac te r is t i c s (e .g . ,

t o t a l d is ch a r ge , p ea k fl o w s , m i n im u m fl o w s , a n d w a t e r

l eve l fluc tua t i on i n l akes) and o ther n ot ab l e hydrol og ic

fea tures and processes i n the wa te r shed (e .g . , co l d wa te r

seeps or g roundwa ter recha rge areas)?

What i s the a r ray an d l andsca pe pa t t e rn o f p lan t

c o m m u n it ie s , a n d w h a t a r e t h e s e ra l s t a g e s in t h e w a t e r -

shed (r ipar i an an d n onr i par ian )? Wha t na tura l processes

c a u s e t h e s e p a t t e r n s (e .g ., fi r e , w i n d , a n d m a s s w a s t in g )?How d o d i f fe rent sys tem s reac t t o these na tura l processes

based on the i r sera l s t ages?

What a re the bas i c morphol og ica l charac te r i s t ic s o f

s t ream va l leys and segment s and th e genera l sed im ent

t r anspor t a nd depos i t ion processes i n the w a te r shed (e .g . ,

s t r a t i fica t i on us i ng accepted c lass i fi ca t i on sys tem s)?


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A Soil Bioengineering Guide - Chapter1 - Making the Connection - Watersheds

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