8 , 4 R e c u r r i n g S t o m E v e n t s
I n N o r t h C a r o l i n a i t i s n o t p o s s i b l e t o f o r e c a s t a m b i e n t water q u a l i t y w i t h o u t t a k i n g s t o r m r u n o f f i n t o a c c o u n t , M o n i t o r i n g o v e r b o t h dzy w e a t h e r
=d s t o r m e v e n t s d u r i n g c r i t i c a l p e r i o d s i s a n e c e s s i t y , Extreme Pow f l o w c o n d i t i o n s r e p r e s e n t p e r i o d s of n o r a i n f a l l and h e n c e n o o v e r l a n d r u n o f f ,
T h e r e i s l i t t l e o r n o c o n t r i b u t i o n f r o m n o n - p o i n t s o u r c e s d u r i n g t h e s e p e r i o d s , m d t h e i r i m p a c t on stream w a t e r q u a l i t y i s a b s e n t , T h e r e i s e v i d e n c e t o show t h a t more s e v e r e c o n d i t i o n s a r e imposed by s t o r m f l o w s , An u n d e r s t a n d i n g of t h e dynamics o f t h e p o l l u t a n t mass f l o w s from nsm-point s o u r c e s d u r i n g s t o r m f l o w s is e s s e n t i a l i f o n e were t o e v a l u a t e t h e i r i m p a c t on a m b i e n t water q u a l i t y . The minimum d a t a r e q u i r e d f r o m a m o n i t o r i n g s y s t e m s h o u l d i n c l u d e s a m p l e s 0 % s t o m e v e n t s ,
P o l l u t a n t c o n c e n t r a t i o n s and mass f l o w s v a r y s i g n i f i c a n t l y w i t h i n a s t o r m e v e n t , The c o n c e n t r a t i o n s i n c r e a s e w i t h d i s c h a r g e d u r i n g t h e r i s i n g l i m b o f t h e h y d r o g r a p h , r e a c h a p e a k ahead of t h e r u n o f f p e a k , and d e e r e a s e t o a l o w e r , more u n i f o r m L e v e l a s r u n o f f c o n t i n u e s , The p o l l u t a n t c o n c e n t r a t i o n s v a r y w i d e l y from s t o r m t o s t o r m , The i m p o r t a n t v a r i a b l e s t h a t c o n t r o l t h e q u a l i t y i n c l u d e r a i n f a l l i n t e n s i t y and d u r a t i o n , a n t e c e d e n t c o n d i t i o n s a n d t h e t y p e o f l a n d u s e ,
The i m p a c t o f u r b a n r u n o f f on t h e DO c o n c e n t r a t i o n s i s complex, The
i n t e r a c t i o n o f c h a n g i n g BOD c o n c e n t r a t i o n s and v a r y i n g r e a e r a t i o n rates p r o d u c e s t h e g r e a t e s t DO d e f i c i t i n t h e s l u g of w a t e r which i n c l u d e s p e a k f l o w , A s
s t o r m s i z e i n c r e a s e s , t h e e f f e c t i s more p r o n o u n c e d , The e f f e c t o f v a r y i n g run- c f f on t i m e o f t r a v e l , r e a c t i o n k i n e t i c s , and s e d i m e n t a t i o n r a t e s s h o u l d be d e t e r m i n e d . T h i s w i l l e x t e n d t h e u s e f u l n e s s of m a t h e m a t i c a l models d e v e l o p e d d u r i n g i n t e n s i v e s u r v e y s ,
F i e l d e s t i m a t e s o f n a n - p o i n t s o u r c e l o a d s m d r e l a t e d r u n o f f c o e f f i c i e n t s s h o u l d b e d e v e l o p e d % o r s t o r m e v e n t s o f d i f f e r e n t f r e q u e n c y and m a g n i t u d e s on s e l e c t e d r u r a l and u r b a n w a t e r s h e d s r e p r e s e n t i n g v a r i o u s t y p e s o f H m d u s e s , The s t o r m w a t e r a n a l y s i s s h o u l d i d e n t i f y t h e stream s e g m e n t s where s i g n i f i c a n t
i m p a c t s are a n t i c i p a t e d ,
The q u a l i t y o f r u n o f f d i s c h a r g e s may b e e x p r e s s e d i n o n e s f t h r e e ways:
1, i n t e r m s of a n a n n u a l a v e r a g e w a s t e l o a d d i s c h a r g e d ,
2, on t h e b a s i s of mass d i s c h a r g e s a s s o c i a r e d w i t h a n i n d i v i d u a l s t o r m , o r
3 , 5 n a real t i m e b a s i s ; i , e , , as a f u n c t i o n o f t i m e d u r i n g a run- o f f e v e n t ,
Each of t h e s e r e p r e s e n t a t i o n s h a s i t s u s e s , I f o n e d e s i r e s t o implement w a t e r q u a l i t y management a l t e r n a t i v e s , t h e q u a l i t y o f r u n o f f must b e known on a s e a l t i m e b a s i s , M a t h e m a t i c a l models h a v e b e e n d e v e l o p e d t o p r e d i c t u r b a n r u n o f f q u a l i t y (24,251. The v e r i f i c a t i o n of t h e m o d e l s i n t h e f i e l d h a s g e n e r a l l y n o t y i e l d e d s a t i s f a c t o r y r e s u l t s ,
The most i m p o r t a n t p o l l u t a n t s found i n u r b a n r u n o f f i n c l u d e f e c a l o r g a n i s m s , s i l t , p e s t i c i d e s , f e r t i l i z e r s , o i l a n d g a s o l i n e , h y d r o c a r b o n s , r o a d s i l t s a n d t a r s , Leaves, and o t h e r s o l i d w a s t e s , S e v e r a l c l a s s i f i e a t i s n s a r e p o s s i b l e f o r t h e s e p o l l u t a n t s s u c h as s o l u b l e o r i n s o l u b l e , c o n s e r v a t i v e o r n o n - c o n s e r v a t i v e , The d i f f i c u l t i e s i n m o n i t o r i n g s t o r m e v e n t s a r i s e due t o t h e h i g h l y v a r i a - b l e n a t u r e o f r u n o f f a n d i t s s l u g e f f e c t s on t h e s t r e a m l a s t i n g f o r r e l a t i v e l y s h o r t l e n g t h s o f t i m e . Problems a r e i n v o l v e d i n s e l e c t i n g p r o p e r s a m p l i n g l o c a - t i o n s which w i l l b e s a t i s f a c t o r y f o r d i f f e r e n t s i z e s t o r m s arad t h e l o g i s t i c s o f b e i n g a t t h e s a m p l i n g l o c a t i o n when t h e s t o r m r u n o f f o c c u r s . T h i s w i l l r e s t r i c t
t h e c h o i c e o f s a m p l i n g l o c a t i o n s a n d t h e s t o r m s t h a t a r e m o n i t o r e d , I t i s r e a - s o n a b l e t o assume t h a t t h e c r i t i c a l p o i n t s w i l l s h i f t d e p e n d f n g on t h e t y p e o f s t o r m and i t s l o c a t i o n on t h e w a t e r s h e d , M o b i l e s a m p l i n g u n i t s o f f e r many a d v a n t a g e s f n m o n i t o r i n g s t o r m r u n o f f q u a l i t y , I n t h i s s i t u a t i o n i t is p r e f e r - a b l e t o t a k e a few s a m p l e s a t a l a r g e number o f s i t e s t h a n t a k i n g many s a m p l e s a t a s i n g l e s i t e , M o b i l e s a m p l i n g w i l l p r o v i d e much b e t t e r d e f i n i t i o n of s p a t i a l v a r i a t i o n . I t w i l l p i n p o i n t t h e l o c a t i o n o f c r i t i c a l p o i n t s which r e m a i n s
e l u s i v e and d i f f i c u l t t o P o e a t e w i t h a f i x e d s a m p l i n g s i t e . I t may a l s o b e h e l p f u l i n d i s c o v e r i n g t h e s h i f t i n t h e l o c a t i o n o f b o t t o m d e p o s i t s ,
8,5 S i g n i f i c a n c e o f Non-point S o u r c e s
T h e r e i s n o p r e c i s e d e f i n i t i o n o f n o n - p o i n t s o u r c e s , I t would a p p e a r t o i n c l u d e a l l p o l l u t a n t s t h a t a c c u m u l a t e on l a n d s u r f a c e s f r o m n a t u r a l and human a c t i v i t i e s and a r e t r a n s p o r t e d t o s t r e a m s by p r o c e s s e s n o t i n v o l v i n g man-made c o l l e c t i o n s y s t e m s , The dominant t r a n s p o r t p r o c e s s f o r p o l l u t a n t s f r o m nom- p o i n t s o u r c e s i s o v e r l a n d r u n o f f of s t o r m w a t e r ,
P o l l u t a n t s c a r r i e d by u r b a n s t o r m w a t e r r u n o f f a r e o f t e n p l a c e d i n a s e p a r a t e c a t e g o r y b e c a u s e t h e y a r e t r a n s p o r t e d i n s t r e e t g u t t e r s , s t o n n s e w e r s y s t e m s , o r combined s e w e r s y s t e m s . However, i n N o r t h C a r o l i n a , t h e r e a r e f e w e x t e n s i v e s t o r m sewer s y s t e m s , S t o r m w a t e r s
are
t r a n s p o l ~ t e d r e l a t i v e l y s h o r t d i s t a n c e s i n s t r e e t g u t t e r s a n d o t h e r d r a i n a g e s t r u c t u r e s b e f o r e t h e y e n t e r n a t u r a l t r i b u t a r y c h a n n e l s t h a t d r a i n t h e u r b a n a r e a s , T h e r e f o r e , u r b a n s t o r m r u n o f f w i l l l a r g e l y b e i n c l u d e d i n t h e g e n e r a l class of n o n - p o i n t s o u r c e s ,Non-point p o l l u t i o n i s a l m o s t e n t i r e l y t h e r e s u l t o f some f o r m o f human
a v a i l a b l e d a t a s u g g e s t t h a t s t o r m w a t e r h a s s e v e r e impacts on DO i n r e c e i v i n g s t r e a m s .
Bryan ( 2 8 ) and C o l s t o n ( 7 ) have c a r r i e d o u t i n t e n s i v e s t u d i e s of s t o r m w a t e r r u n o f f i n a 1069-acre urban watershed i n Durham, North C a r o l i n a , T h e i r f i n d i n g s i n d i c a t e c o n t r i b u t i o n s of oxygen-demanding s u b s t a n c e s and t o t a l s o l i d s f a r i n e x c e s s of t r e a t m e n t p l a n t e f f l u e n t s d u r i n g and a f t e r s t o r m s , A s a r e s u l t of s e v e r a l o t h e r s t u d i e s , s u f f i c i e n t e v i d e n c e h a s been accumulated t o show t h a t n s n - p o i n t s o u r c e s d u r i n g a d a f t e r storms a r e l i k e l y t o be a
major problem i n comparison w i t h t h e e f f l u e n t s from secondary w a s t e w a t e r t r e a t - ment p l a n t s ,
8 , h E s t i m a t e s of Non-point S o u r c e s
Three t y p e s o f non-point p o l l u t i o n pose p o t e n t i a l t h r e a t t o ambient w a t e r q u a l i t y :
I , r u r a l r u n o f f , e s p e c i a l l y from animal p r o d u c t i o n , 2 , urban s t o r m w a t e r r u n o f f , and
3. b e n t h i c c o n t r i b u t i o n s below l a r g e t r e a t m e n t p l a n t o u t f a l l s ,
S u b s t a n t i a l q u a n t i t i e s of p o l l u t a n t s a r i s e from r u r a l a r e a s , Although a c t i v i t i e s i n urban a r e a s g e n e r a t e Large l o a d s of p o l l u t a n t s , t h e y r e p r e s e n t a v e r y s m a l l p e r c e n t a g e o f l a n d u s e i n North C a r o l i n a , L i t t l e e f f o r t h a s been made t o
c o l l e c t f i e l d d a t a on non-urban, non-point l o a d s i n a manner t h a t would p e r m i t a p p l i c a t i o n of r e s u l t s t o u s a m p l e d a r e a s w i t h a r e a s o n a b l e l e v e l o f c o n f i d e n c e , I n 1973, EPA G u i d e l i n e s were i s s u e d f o r i d e n t i f y i n g and e v a l u a t i n g t h e n a t u r e and e x t e n t o f non-point s o u r c e s f o r a g r i c u l t u r a l , s i l v i c u l t u r a l , mining, and c o n s t r u c t i o n a c t i v i t i e s , The methodology can b e used f o r rough f i r s t - c u t e s t i m a t e s of p o l l u t i o n from t h o s e s o u r c e s ,
There a r e v e r y l i t t l e d a t a on minor s t r e a m s , some of which may c a r r y l a r g e non-point l o a d s , I n g e n e r a l , t h e s e s t r e a m s c a r r y v e r y s m a l l dry-weather f l o w s and a r e n o t of major importance t o e h e w a t e r economy of t h e a r e a , However, e x p l i c i t a t t e n t i o n s h o u l d b e g i v e n t o a l l s t r e a m s o f t h e a r e a t o d e t e r m i n e i f f u r t h e r i n v e s t i g a t i o n o f s e l e c t e d minor s t r e a m s i s n e c e s s a r y ,
Storm w a t e r impact m o n i t o r i n g s h o u l d b e u n d e r t a k e n o n l y on t h o s e segments of s t r e a m s where s i g n i f i c a n t i m p a c t s a r e a n t i c i p a t e d , P r e l i m i n a r y e s t i m a t e s of non-point l o a d s a r e r e q u i r e d t o p i n p o i n t c a n d i d a t e l o c a t i o n s , Two c a s e s a r i s e :
1, t h e r e i s no e x t e n s i v e f i e l d d a t a on t h e w a t e r s h e d , o r 2 , w a t e r q u a l i t y d a t a f o r t h e r i v e r segment and e s t i n a t e s of
p o i n t s o u r c e s a r e a v a i l a b l e ,
I n t h e a b s e n c e of e x t e n s i v e f i e l d d a t a , a s e t of e s t i m a t e s can b e p r e p a r e d on t h e b a s i s of E m d - u s e i n v e n t o r y and t h e c o n t r i b u t i o n c o e f f i c i e n t s r e p o r t e d i n t h e l i t e r a t u r e f o r e a e h t y p e of l a n d u s e , The l a n d u s e i n v e n t o r i e s s h o u l d b e p r e p a r e d on a w a k r s h e d b a s i s , Non-point s o u r c e l o a d s
for
e a e h o f t h e d r a i n a g e u n i t s may t h e n b e d e r i v e d b y m u l t i p l y i n g t h e l e v e l s o f a c t f v i t i e s w i t h i n e a c h u n i t b y t h e r u n o f f c o e f f i c i e n t , To t h e e x t e n t p o s s i b l e , l o a d s s h o u l d b e e s t i - mated f o r BOD, TOC, n i t r o g e n , and i t s components and f o r s u s p e n d e d s o l i d s ,I n p l a c e s where w a t e r q u a l i t y d a t a a r e a v a i l a b l e , e s t i m a t e s f o r n o n - p o i n t s o u r c e l o a d s c a n b e c o n s t r u c t e d by t a k i n g t h e d i f f e r e n c e between t h e stream l o a d s and e s t i m a t e d p o i n t l o a d s , T o t a l mass rates o f f l o w c a n b e c a l c u l a t e d where b o t h c o n c e n t r a t i o n s o f p o % l u t m t s and stream f l o w s
are
a v a i l a b l e , By s u b t r a c t i n g p o i n t l o a d s , a d j u s t e d f o r a t t e n u a t i o n b e t w e e n I s c a t i on o f d i s e h a r g e s=d s a n p l i n g b o c a t i o n s , n o n - p o i n t l o a d s c a n b e e s t i m a t e d , S t r e a m f l o w a n d i t s r e l a t i o n s h i p t o mean f l o w s and low f l o w s s h o u l d accompany s u c h e s t i m a t e s ,
d-use a c t i v i t i e s c o n t r i b u t i n g t o e a c h l o c a t i o n shouLd a l s o b e r e p o r t e d , E s t i m a t e s o f n o n - p o i n t l o a d s s h o u l d b e d e v e l o p e d f o r two l e v e l s of a r e a l c o v e r a g e , E s t i m a t e s s h o u l d b e p r e p a r e d f o r l a r g e w a t e r s h e d s i n t h e r a n g e o f 25 t o 1 5 0 s q u a r e m i l e s and ow which p o i n t l o a d s a r e small i n c o m p a r i s o n w i t h a n t i - c i p a t e d n o n - p o i n t l o a d s . Loads from w a t e r s h e d s 02: t h i s s i z e p r o b a b l y c s n n o t b e e s t i m a t e d by s i m p l y a d d i n g e s t i m a t e s from s m a l l a r e a l u n i t s w i t h i n t h e w a t e r - s h e d s upon which l a n d u s e s a r e homogeneous, D e g r a d a t i o n , s e d a m e n t a t i o n , a n d o t h e r phenomena o c c u r r i n g w i t h i n l a r g e w a t e r s h e d s p r o b a b l y r e d u c e t h e t o t a l l a a d f r o m t h e s e a r e a s t o l e v e l s much below t h e sum of c o n t r i b u t i o n s f r o m s u b - a r e a s w i t h i n t h e w a t e r s h e d , The s e t sf w a t e r s h e d s s h o u l d r e f l e c t a m i x t u r e s f t h e predominant l a n d u s e s ,
E s t i m a t e s f r o m n o n - p o i n t l o a d s i n u r b a n a r e a s s h o u l d b e d e v e l o p e d f o r a s e t of small u r b a n w a t e r s h e d s i n t h e r a n g e o f 3 t o 1 0 s q u a r e m i l e s , The w a t e r - s h e d s s h o u l d b e s e l e c t e d s o t h a t l a n d u s e s w i t h i n w a t e r s h e d s a r e r e l a t i v e l y homogeneous and l a n d u s e s i n a 9 1 w a t e r s h e d s r e p r e s e n t a b r o a d r a n g e o f u r b a n
Band u s e s , 8 . 7
The recommended s t r a t e g y f o r ~ b t a i n i n g i n f o m a t i o n on t h e i m p a c t af s t o r m w a t e r f l o w s on s t r e a m w a t e r q u a l i t y i n v o l v e s two l e v e l s of a n a l y s i s , The
o b j e c t i v e o f t h e f i r s t l e v e l a n a l y s f s i s t o d e t e c t m y i n m e d i a t e i m p a c t of s t o r m water r u n o f f on DO l e v e l s a d r o e s t a b l i s h f r e q u e n c y d i s t r i b u t i o n o f DO v a r i a -
t i o n a s s o c i a t e d w i t h s t o r m e v e n t s , The DO v a r i a t i o n s must b e c o r r e l a t e d w i t h
s t o r m f l o w s and w i t h r a i n f a l l measurements. T h i s may r e q u i r e c o n t i n u o u s moni- t o r i n g o f DO l e v e l s a t two l o c a t i o n s where t h e most a d v e r s e PO i m p a c t s a r e known t o e x i s t d u r i n g d r y w e a t h e r c o n d i t i o n s and a r e assumed t o e x i s t d u r i n g and
a f t e r storm e v e n t s . The r e c o r d s should be l o n g - t e r n , a t l e a s t o n e - y e a r ' s d u r a - t i o n , from which r e l i a b l e e s t i m a t e s s f f r e q u e n c y d f s t r f b z t i o n of i m p a c t s and t h e s e a s o n a l e f f e c t s c a n b e c o n s t r u c t e d . As t h e s a g p o i n t i s e x p e c t e d t o s h i f t w i t h t h e s i z e of t h e storm, m o b i l e m o n i t o r i n g may b e a d v a n t a g e o w ,
The second l e v e l s f a n a l y s i s w i l l a l l o w mass b a l a n c e s o f v a r i o u s c o n s t i t u e n t s t o be sampled. The time-sequenced samples s h o u l d be o b t a i n e d t h r o u g h t h e u s e o f s t a g e - a c t u a t e d a u t o m a t i c s a m p l e r s , R a i n f a l l and s u r f a c e flow measurements s h o u l d b e t a k e n s i m u l t a n e o u s l y w i t h t h e w a t e r q u a l i t y sampling, A minimum of two r e c o r d i n g r a i n f a l l gages s h o u l d b e l o c a t e d i n t h e s u b - a r e a b e i n g sampled.
Stream gages s h o u l d b e i n s t a l l e d , i f r e q u i r e d ,
P a r a m e t r i c c o v e r a g e of a l l a u t o m a t i c samplfng s t a t i o n s s h o u l d i n c l u d e t o t a l o r g a n i c c a r b o n , t o t a l suspended s o l i d s , s p e c i e s s f n i t r o g e n , t o t a l phosphorus and t o t a l o r t h o p h o s p h a t e . Grab samples s h o u l d b e t a k e n f o r t h e d e t e r m i n a t i o n o f BODj. BOD long-term, and n i t r o g e n - i n h i b i t e d BOD t o g a i n i n s i g h t i n t o t h e k i n e - t i c s s f decomposition of s u b s t a n c e s b e i n g t r e n s p o r ~ e d E n t s t h e c r i t i c a l segments.
The sampling i n t e r v a l s h o u l d be s e t s o a s t o d e f i n e t h e r i s i n g a n d f a l l i n g l i m i t s f t h e hydrograph, It i s c o n j e c t u r e d t h a t t h i s would b e between one-half and one hour. The d u r a t i o n o f sampling w i l l be s e t a t 24 h o u r s ,
8,8 Sample Surveys s f Non-point Sources
Non-point s o u r c e s a r e enormously g r e a t i n number. I n e a c h d r a i n a g e b a s i n , t h e r e i s a v a s t network of minor t r i b u t a r y c h a n n e l s , Monitoring of a l l non- p o i n t s o u r c e s i n a l l r i v e r b a s i n s would be a v e r y e x p e n s i v e u n d e r t a k i n g . Such a s t u d y would p r o b a b l y be i n e f f i c i e n t b e c a u s e much o f t h e d a t a r e q u i r e d from a n e x h a u s t i v e m o n i t o r i n g e f f o r t would be r e d u n d a n t , The obvious r e c o u r s e would b e t o some t y p e of sampling t e c h n i q u e ,
The f i r s t s t e p i n d e v i s i n g a sampling scheme i s t h e d e f i n i t i o n of t h e p o p u l a t i o n ; i.e., t h e s e t s f a l l i t e m s t o b e i n c l u d e d , O r d i n a r i l y , i t i s n o t n e c e s s a r y t o i n c l u d e every Past brook i n t h e p o p l a t i o n . There i s some lower bound on t h e o r d e r o f t h e s t r e a m t h a t s h o u l d be c o n s i d e r e d , I d e a l l y , one would go up t o t h e l e v e l a t which g e n e r a l l a n d u s e w i t h i n each w a t e r s h e d i s
r e l a t i v e l y homogeneous. I n most d r a i n a g e b a s i n s , t h e h i g h e s t t h r e e o r d e r s of t h e s t r e a m w i l l s u f f i c e u n l e s s a t r i b u t s r y s f Power
erder
h a s s a n e s p e c i a l f e a t u r e s which need t o be c o n s i d e r e d ,102
I n t h e i r c o n t r i b u t i o n o f p o l l u t i o n a l l o a d s , t h e n o n - p o i n t s o u r c e s a r e h i g h l y v a r i e d . I t i s , however, p o s s i b l e t o d i v i d e t h i s h e t e r o g e n e o u s p o p u l a - t i o n i n t o d i s t i n g u i s h a b l e g r o u p s which a r e l i k e l y t o p r o d u c e i n f o r m a t i o n which i s similar w i t h i n e a c h g r o u p b u t d i f f e r s f r o m g r o u p t o g r o u p . T h e s e g r o u p s a r e c a l l e d s t r a t a . A more a c c u r a t e e s t i m a t e o f any s t r a t u m mean can b e o b t a i n e d from a small sample o f s u i t a b l e p r o p o r t i o n s t o g i v e an e s t i m a t e f o r t h e whole p o p u l a t i o n i n a d r a i n a g e b a s i n ,
The v a r i a b l e s which c a n b e u s e d f o r s t r a t i f i c a t i o n a r e : 1. p h y s i o g r a p h i c s o i l s a n d g e o l o g i c ~ o n d i t i o n s ,
2 . o r d e r o f s t r e a m , 3 . t y p e o f l a n d u s e , and 4. ground water c o n t r i b u t i o n .
The t h r e e p h y s i o g r a p h i c r e g i o n s of N o r t h C a r o l i n a (Mountain, P i e d m o n t , a n d C o a s t a l P l a i n ) d i f f e r i n s l o p e s , t y p e s o f r o c k and d r a i n a g e c h a r a c t e r i s t i c s of s o i l , E x c e l l e n t c o r r e l a t i o n s h a v e b e e n e s t a b l i s h e d b e t w e e n stream o r d e r and v a r i o u s d r a i n a g e b a s i n g e o m e t r i c and h y d r o l o g i c p a r a m e t e r s , The h i g h e r t h e s t r e a m o r d e r , t h e g r e a t e r i s t h e f l o w and i n t e g r a t i n g c a p a b i l i t y w i t h r e s p e c t t o t h e w a t e r q u a l i t y p a r a m e t e r s . I n t y p e o f l a n d u s e o n e h a s t o d i f f e r e n t i a t e between
1. n a t u r a l f o r e s t ,
2 . a g r i c u l t u r a l u s e : (a) p a s t u r e , ( b ) row c r o p s , a n d ( c ) l i v e - s t o c k p r o d u c t i o n , a n d
3 . u r b a n : ( a ) r e s i d e n t i a l , a n d ( b ) i n d u s t r i a l l a n d s .
Economic d e v e l o p m e n t , c h a n g e s i n t e c h n o l o g y , l a n d u s e p o l i c i e s and r e s p o n s e t o r e g u l a t o r y m e a s u r e s a r e l i k e l y t o a l t e r t h e c o m p o s i t i o n of e a c h s t r a t u m o v e r t i m e s o t h a t t h e y must b e p e r i o d i c a l l y u p d a t e d . The e x t e n t o f i n t e r c h a n g e
between s u r f a c e and ground w a t e r s h a s p r o f o u n d e f f e c t on i n s t r e a m w a t e r q u a l i t y , The f i r s t t a s k w i l l b e t o d e f i n e t h e s e t o f a l l s o u r c e s a n d t o d e t e r m i n e t h e c o m p o s i t i o n of e a c h s t r a t u m . I n g e n e r a l , t h e s t r a t a w i l l n o t b e of e q u a l s i z e ; t h e s t r e a m s o f l o w e r o r d e r w i l l be more numerous, I t i s assumed t h a t f o r economic r e a s o n s t h e t o t a l s a m p l e s i z e f o r n o n - p o i n t s o u r c e s i s f i x e d . I n a s t r a t i f i e d random s a m p l i n g , t h e v a r i a n c e o f t h e estimate o f t h e mean i s m i n i - mized f o r a f i x e d t o t a l s i z e o f sample n , i f t h e sample s i z e from s t r a t u m h i s e q u a l t o (18)
where N i s t h e number o f e l e m e n t s i n s t r a t u m h and S i s t h e s t a n d a r d d e v i a -
h h
t i o n o f t h e q u a l i t y p a r a m e t e r f o r which t h e s a m p l e i s b e i n g t a k e n . T h i s r e l a - t i o n s h i p l e a d s t o t h e f o l l o w i n g r u l e of c o n d u c t : i n a g i v e n s t r a t u r n t a k e a l a r g e r sample i f t h e s i z e o f t h e s t r a t u m i s l a r g e r o r i f t h e s t r a t u m i s more v a r i a b l e i n t e r n a l l y , T h i s a l l o c a t i o n i s c a l l e d o p t i m a l a l l o c a t i o n s i n c e i t r e s u l t s i n t h e e s t i m a t i o n o f t h e p o p u l a t i o n mean w i t h t h e l e a s t p o s s i b l e s t a n d - a r d e r r o r , A random s a m p l e o f a p p r o p r i a t e s i z e i s t h e n drawn f r o m e a c h s t r a t u m .
B e f o r e t h e s a m p l e s i z e can b e d e t e r m i n e d , t h e s t r a t a v a r i a n c e s m u s t b e known o r b e e s t i m a t e d . I f n o i n f o r m a t i o n is a v a i l a b l e o n t h e v a r i a n c e s o f t h e p a r a m e t e r s , a p i l o t m o n i t o r i n g program may h a v e t o b e d e v i s e d , As a f i r s t a p p r o x i m a t i o n o f t h e v a r i a b i l i t y o f a p a r a m e t e r , t h e s t a n d a r d d e v i a t i o n o f s t r e a m f l o w may b e u s e d , With t h i s a l l o c a t i o n , more stream s e g m e n t s w i l l b e m o n i t o r e d from t h e s t r a t a where i t i s most n e e d e d ; i , e , , t h o s e w h e r e t h e c h a n c e s o f a n u n r e p r e s e n t a t i v e s e t o f r e s p o n s e s i s h i g h e r b e c a u s e of t h e g r e a t e r p o t e n - t i a l v a r i a b i l i t y o f r e s p o n s e .
I f no t h i n g i s known a b o u t t h e s t r a t u m v a r i a n c e s o f a p a r a m e t e r , propoar- t i o n a t e s a m p l i n g may b e u s e d , I n t h i s scheme, t h e sampled f r a c t i o n i s t h e same f o r a l l s t r a t a a n d
The m o n i t o r i n g s i t e s s h o u l d b e l o c a t e d a t t h e mouths o f t h e t r i b u t a r i e s d r a i n i n g t h e f r w a t e r s h e d s .
C h a p t e r 9
NBN-POINT
SOURCES : A CASE STUDY 9 . 1 I n t r o d u c t i o nThe s t u d y area c o m p r i s e s c o m p l e t e h y d r o l o g i c s u b - u n i t s a n d c a n , w i t h minor e x c e p t i o n s , b e d e f i n e d as t h e l a n d l y i n g i n t h e New Hope R i v e r w a t e r s h e d a n d i n t h e Neuse R i v e r B a s i n above t h e mouth o f Middle C r e e k n e a r S m i t h f i e l d . W i t h i n t h e a r e a , a s d e f i n e d a l o n g h y d r o l o g i c b o u n d a r i e s , t h e Neuse B a s i n c o n t a i n s 1220 s q u a r e m i l e s a n d t h e New Hope B a s i n c o n t a i n s 338 s q u a r e m i l e s , M a j o r w a t e r - s h e d s i n t h e Neuse B a s i n a r e t h o s e o f t h e Eno R i v e r (273 s q , m i , ) , t h e F l a t R i v e r (172 s q . m i , ) , C r a b t r e e Creek (146 s q , m i . ) , Walnut Creek (46 s q , m i , ) , S w i f t Creek (154 s q , m i , ) , a n d M i d d l e Creek (146 s q , m i , ) , I n t h e New Hope B a s i n t h e m a j o r w a t e r s h e d s are t h o s e o f New Hope C r e e k (70 s q , m i , t o mouth o f L i t t l e C r e e k ) , L i t t l e Creek (25 s q , m i . ) , N o r t h e a s t Creek (47 s q , m i , ) , and Morgan Creek ( 6 5 s q . m i , ) .
R a i n f a l l s t a t i s t i c s a r e n e a r l y u n i f o r m a c r o s s t h e a r e a , Over t h e p e r i o d 1 9 2 1 t o 1 9 7 1 t h e a n n u a l r a i n f a l l a v e r a g e d 45 $ 7 i n c h e s . H i g h e s t monthly r a i n - f a l l s o c c u r i n J u l y a n d A u g u s t , and t h e g r e a t e s t v a r i a t i o n i n m o n t h l y r a i n f a l l a l s o o c c u r s d u r i n g t h e summer months, R a i n f a l l d u r i n g t h e s e months a l s o t e n d s t o b e more i n t e n s e t h a n i n o t h e r m o n t h s ; i t o f t e n a c c o m p a n i e s v i o l e n t
t h u n d e r s t o r m s , and a t t i m e s , e x t r e m e l y heavy r a i n f a l l s are i n d u c e d by h u r r i - c a n e s moving a l o n g t h e A t l a n t i c C o a s t ,
Annual s u r f a c e r u n o f f f r o m t h a t r a i n f a l l a v e r a g e s a p p r o x i m a t e l y 1 3 , 6 i n c h e s , o r r o u g h l y 3 0 p e r c e n t o f t h e r a i n f a l l , %en t h a t r u n o f f 1s e x p r e s s e d as a rate o f f l o w i n streams p e r u n i t a r e a of c o n r r i b u t i n g w a t e r s h e d , the run- o f f a v e r a g e s a p p r o x i m a t e l y 1 . 0 c u b i c f e e t p e r s e c o n d p e r s q u a r e m i l e o f d r a i n a g e area, S t r e a m f l o w s t a t i s t i c s a t s e l e c t e d g a g i n g s t a t i o n s s h o m i n F i g u r e 6
i n d i c a t e c o n s i d e r a b l e v a r i a t i o n s i n u n i t r u n o f f r a t e s i n t h e d i f f e r e n t w a t e r - s h e d s , e s p e c i a l l y d u r i n g summer months.
H i g h e s t r u n o f f r a t e s a r e found d u r i n g t h e w i n t e r a d l o w e s t rates o c c u r d u r i n g t h e p e r i o d J u n e t o O c t o b e r , j u s t t h e r e v e r s e of h i g h and low r a i n f a l l s , T h i s d i f f e r e n c e i n d i c a t e s t h e p r o f o u n d e f f e c t of t e m p e r a t u r e on e v a p o r a t i o n and e v a p o - t r a n s p i r a t i o n r a t e s , V a r i a t i o n s i n w a t e r t e m p e r a t u r e i n t h e a r e a t e n d t o l a g a m b i e n t t e m p e r a t u r e s by a p p r o x i m a t e l y one month, a n d t h e y t e n d t o v a r y o v e r a s m a l l e r i n t e r v a l , 35'
-
85' F,A c o m b i n a t i o n o f h i g h l y v a r i a b l e r a i n f a l l , h i g h l y i m p e r v i o u s s o i l s w i t h l i t t l e g r o u n d w a t e r s t o r a g e , and a wide v a r i a t i o n i n t e m p e r a t u r e create l a r g e
105
v a r i a t i o n s i n s t r e a m f l o w , S t a n d a r d v a r i a t i o n s o f m o n t h l y f l o w s a t s e l e c t e d s t a t i o n s a r e shown i n F i g u r e 6 ; f l o w - d u r a t i o n c u r v e s f o r d a i l y f l o w s a t s e v e r a l g a g i n g s t a t i o n s a r e shown i n F i g u r e 3. The l a t t e r f i g u r e r e v e a l s t h a t f l o w s a s small as 0 . 0 1 c f s l s q , m i . a r e e x p e r i e n c e d f r o m 2-5 p e r c e n t o f t h e t i m e , w h i l e f l o w s as s m a l l as 0 , l c f s / s q . m i , are r e a l i z e d from 8-12 p e r c e n t o f t h e t i m e , M e d i a l f l o w s , r a n g i n g f r o m 0 . 2 t o 0 , 5 c f s / s q , m i , , a r e much less t h a n t h e a v e r a g e f l o w s , T h e s e low f l o w s o f t e n o c c u r d u r i n g summer months when tem- p e r a t u r e s a r e a t t h e i r p e a k s and r e l a t e d s a t u r a t i o n l e v e l s o f d i s s o l v e d oxygen a r e a t t h e i r l o w e s t , These two f a c t o r s combine t o r e d u c e t h e c a p a c i t i e s o f s t r e a m s t o a s s i m i l a t e w a s t e s t o t h e i r l o w e s t l e v e l s d u r i n g l a t e summer a n d e a r l y f a l l , A l t h o u g h t h e d a t a on s e a s o n a l v a r i a t i o n s i n n o n - p o i n t s o u r c e s are l i m i t e d , c u l t i v a t i o n and c o n s t r u c t i o n a c t i v i t i e s and t h e sudden a n d i n t e n s e c h a r a c t e r of t h u n d e r s t o r m s and r e l a t e d h i g h v e l o c i t i e s o f r u n o f f l e a d t o t h e h y p o t h e s i s t h a t l o a d s from t h e s e s o u r c e s a r e h e a v i e s t d u r i n g t h i s p e r i o d a l s o ,
Water r e s o u r c e s o f t h e a r e a h a v e b e e n u s e d p r i m a r i l y f o r p u b l i c w a t e r s u p p l i e s a n d d i s p o s a l o f w a t e r - b o r n e w a s t e s , The F l a t R i v e r w a t e r s h e d h a s b e e n u s e d f o r many y e a r s as a collection g r o u n d s f o r Durham's w a t e r s u p p l y ; H i l l s - borough draws i t s s u p p l y f r o m t h e Eno R i v e r , and Chapel H i l l - C a s r b o r o t a k e s i t s s u p p l y from u p l a n d s o f Morgan C r e e k , R a l e i g h ' s w a t e r i s t a k e n f r o m Walnut Creek and t h e Neuse R i v e r , T h e r e a r e s m a l l g r o u n d w a t e r s u p p l i e s i n e a s t e r n and
s o u t h e r n p o r t i o n s o f Wake County, b u t ground w a t e r a q u i f e r s i n t h e a r e a h a v e s m a l l y i e l d s and v a r y c o n s i d e r a b l y f r o m o n e l o c a t i o n t o a n o t h e r , The New Hope R i v e r below U,S, Highway 95-501 and s e v e r a l o f i t s t r i b u t a r i e s a r e u s e d p r i - m a r i l y as c a r r i e r s of u r b a n waste f r o m Durham a n d Chapel H i l l , E l L e r b e Creek
a n d a p o r t i o n of t h e Neuse R i v e r below E L l e r b e Creek a r e u s e d f o r d i s p o s a l of w a s t e s from Durham, w h i l e t h e l o w e r p o r t i o n o f Walnut Creek and t h e Neuse
R i v e r between R a l e i g h a n d Smi t h f i e l d a r e u s e d f o r d i s p o s a l o f ~ a l e f g h ' s w a s t e s a T h e r e a r e n o s u b s t a n t i a l h y d r o e l e c t r i c i n s t a l l a t i o n s i n t h e area, a n d r e c r e a t i o n a l u s e s o f w a t e r a r e g e n e r a l l y l i m i t e d t o w a t e r s u p p l y r e s e r v o i r s and f a r m p o n d s , The s t r e a m s a r e s h a l l o w and a r e g e n e r a l l y Located a b o v e t h e f a l l S i n e between t h e Piedmont and C o a s t a l P l a i n s g e o l o g i c r e g i o n s o f N o r t h Caro- l i n a ; a n d t h e r e f o r e , t h e y h a v e n e v e r b e e n u s e f u l f o r n a v i g a t i o n , I r r i g a t i o n o f c r o p l a n d s i s p r a c t i c e d s p a r i n g l y , C r a b t r e e C r e e k h a s r e c e i v e d s p e c i a l a t t e n t i o n b e c a u s e of f l o o d damage e x p e r i e n c e d i n i t s f l o o d p l a i n s w f t h f n t h e C i t y of R a l e i g h ,
FIGURE
6
MONTHLY STREAMFLOW STAT I ST1 CS AT SELECTED GAG I NG STAT1 ONS.01 .1 f
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Streamflow in cubic feet per second per squaremile of drainage area
9 , 2 P o i n t S o u r c e s and L o a d s
The most c o m p l e t e f i l e s on p o i n t s o u r c e s of p o l l . u t i o n i n t h e a r e a a r e main- t a i n e d b y t h e D i v i s i o n o f E n v i r o n m e n t a l Management, N o r t h C a r o l i n a Department o f N a t u r a l a n d Economic R e s o u r c e s , and t h e s e i n v e n t o r i e s h a v e b e e n p u b l i s h e d
r e c e n t l y i n p l a n s f o r t h e Neuse a n 3 Cape F e a r R i v e r B a s i n s ( 2 9 1 , S u p p l e m e n t a r y i n f o r m a t i o n a n d a n a l y s e s of e x i s t h g d a t a a r e a v a i l a b l e i n a 1 9 7 % s t u d y o f n u t r i e n t d i s c h a r g e i n t h e Haw and New Hope s u b - b a s i n s i n t h e Cape F e a r R i v e r B a s i n (301, a 1 9 7 3 r e v i e w s f t h e p r o p o s e d F a l l s of t h e Neuse R e s e r v o i r b y EPA
(3%),
a n d i n t e n s i v e s u r v e y s of p o r t i o n s of t h e Meuse and New Hope R i v e r s i n 1 9 7 3 (321, These s o u r c e s and s e l e c t e d c h a r a c t e r i s t i c s sf t h e i r d i s c h a r g e s a r e L i s t e d i n T a b l e 38,C o n s t i t u e n t s of t h e s e w a s t e s
which
a r e o f m a j o r c o n e e r n i n managing t h e q u a l i t y o f w a t e r i n t h e area a n d f o r w h i c h d a t a s e t s a r e moss c o m p l e t e T n c l u d e oxygen demand as measured by BOD n i t r o g e n , a n d p h o s p h o r o w , E s t i m a t e s of5
"
l o a d s o f t h e s e s u b s t a n c e s t h a t a r e d i s c h a r g e d t o s t r e a m s a r e v a r i a b l e f r o m o n e d a t a s o u r c e t o m o t h e r b u t w i t h t h e e x c e p t i o n o f e s t i m a t e s by EPA on n i t r o g e n and phosphorous l o a d s i n t h e u p p e r Neuse B a s i n , e s t i m a t e s o f t o t a l l o a d s f r o m m a j o r s u b - b a s i n s a r e r o u g h l y c o m p a r a b l e ; a n d t h e y are c o m p a t i b l e w i t h s t r e a m l o a d s as measured d u r i n g t h e 1 9 7 3 i n t e n s i v e s u r v e y s of s t r e a m ,
F i r s t a p p r o x i m a t i o n s t o t h e s e l o a d s a r e g i v e n i n T a b l e 39, E s t i m a t e s of i o a d s i n t h e New Hope B a s i n are b a s e d on v a l u e s r e p o r t e d i n T a b l e 3 8 t a k e n f r o m t h e r e c e n t l y p u b l i s h e d b a s i n p l a n s , v a l u e s r e p o r t e d i n
the
1 9 7 1 s u r v e y , a n d v a l u e s r e p o r t e d d u r i n g t h e i n t e n s i v e s u r v e y s i n 1 9 7 3 ,There
a r e discrepancies among t h e s e d a t a s o u r c e s , b u t t h e t o t a l s f o r t h i s s u b - b a s i nare
r o u g h l y 5200 pounds p e r day o f BOD5, 1900 p ~ u n d s p e r day of n i t r a g e n , and 600 pounds p e r d a y o f p h o s p h o r o u s , Most o f t h e s e l o a d s a r e d f s c h a r g e d from t h e Chapel H i l l w a s t e t r e a t m e n t p l a n t and t h e Sandy C r e e k , New Hope, T h i r d F o r k C r e e k , and Hope V a l l e y p l a n k s i n Durham, A p p r o x i m a t e l y h a l f o f t h e l o a d s a r e g e n e r a t e d by Chapel H i l l a n d t h e o t h e r h a l f b y Durham,E s t i m a t e s o f l o a d s from t h e Upper Neuse B a s i n are
based
on v a l u e s g i v e n i n T a b l e 38 and t h e p r i o r a n a l y s i s by EPA, L a r g e s t c o n t r i b u t o r s t o t h e s e l o a d s i n c l u d e H ~ l l s b o s o u g h ; t h e N o r t h s i d e , Eno R i v e r , a n d L i c k Creek p l a n t s i n Durham;B u t n e r H o s p i t a l ; a n d C r e e d n o o r , E s t i m a t e s of BOD made by EPA and t h o s e b a s e d 5
on T a b l e 38 a r e c o m p a r a b l e a n d t o t a l about 3100 pounds p e r d a y , EPA e s t i m a t e d l o a d s o f 5300 and 3000 pounds p e r day o f n i t r o g e n a n d p h o s p h o r o u s , r e s p e c t i v e l y , b a s e d on f a c t o r s o f 0 , 0 4 2 and 0 , 0 0 7 pounds p e r day p e r c a p i t a , However, t h e s e f i g u r e s c o r r e s p o n d t o much h i g h e r c o n c e n t r a t m n L e v e l s i n p l a n t e f f l u e n t s t h a n
Durham
t h o s e r e p o r t e d i n t h e i n t e n s i v e s u r v e y , a n d t h e t o t a l l o a d s are mu& h i g h e r t h a n measured i n - s t r e a m l o a d s , Data r e p o r t e d i n t h e i n t e n s i v e s u r v e y s and r a t i o s
~f
n i t r o g e n and p h o s p h o r o u s t oBOD
i n t h e New Hope s u r v e y i n1971
w e r e u s e d to5
c o n s t r u c t t h e l o w e r e s t i m a t e s s f 1000 and 200 pounds p e r day o f n i t r a g e n and p h o s p h o r o u s , r e s p e c t i v e l y , r e p o r t e d i n T a b l e 3 9 ,
T a b l e 39