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<br />
<br />
<br />Freshwater Delivery to
<br />Pamlico Sound
<br />
<br />Pamlico Sound is a relatively
<br />shallow lagoonal estuary with a
<br />mean depth of 16 feet and a surface
<br />area of2,060 mi2 (Giese and others,
<br />1985), The Sound is bounded on the
<br />seaward side by the Outer Banks, a
<br />barrier island system that restricts
<br />water exchange with the Atlantic
<br />Ocean through four small inlets. The
<br />Chowan River, Roanoke River, and
<br />several small rivers drain to Albe-
<br />marle Sound, which then drains
<br />southward to Pamlieo Sound or to the
<br />Atlantic Ocean through one oflhe
<br />four inlets. Sixty percent of the total
<br />Pamlico Sound drainage area is in the
<br />basin that drains to Albemarle Sound
<br />(table 5).
<br />The ratio of the volume of Pam-
<br />lico Sound (920 billion eubic feet
<br />[fi3]) to the average annual inflow
<br />(32,000 cubic feet per second [fi3/s])
<br />from the entire basin, including the
<br />Albemarle Sound drainage, yields a
<br />
<br />theoretical freshwater replacement
<br />time of about II months. Actual res-
<br />idence time is likely longer for many
<br />locations in Pamlico Sound because
<br />of restricted circulation, the short-
<br />circuiting of some inflows, and the
<br />position of the tidal inlets relative to
<br />the major freshwater inflows. Long
<br />water residence times, small tidal
<br />amplitude (1.0-1.5 feet), and slow-
<br />flowing tributaries make Pamlico
<br />Sound an effective trap for dissolved
<br />and particulate matter.
<br />Freshwater inflow to Pamlieo
<br />Sound was estimated for September
<br />and Oetober 1999. Flows were deter-
<br />mined from data collected at the
<br />USGS network of streamgages in
<br />North Carolina and Virginia (fig. 7)
<br />and from estimates of flow from
<br />ungaged areas, Streamflow from
<br />67.7 percent of the land area draining
<br />to Pamlieo Sound is gaged. Rainfall
<br />on the surface of Albemarle Sound
<br />and Pamlico Sound was estimated
<br />from raingage and Doppler radar
<br />measurements, and the rainfall
<br />
<br />volume was converted to a flow rate
<br />for comparison with streamflow. The
<br />volume of freshwater inflow as a per-
<br />centage of Pamlico Sound volume
<br />was computed by converting the
<br />monthly mean flow rate to a total
<br />volume for the month, and then
<br />dividing the freshwater inflow
<br />volume by the volume of Pamlico
<br />Sound, Nonnal inflow was computed
<br />from long-tenn monthly mean
<br />streamflow records. The period of
<br />streamflow record at the various
<br />stream gages used in the analysis
<br />ranged from about 15 years to more
<br />than 100 years.
<br />Freshwater inflow volume to the
<br />head of the Pamlico River estuary
<br />(near site 18, fig, 7) during the month
<br />of September was more than 90 per-
<br />cent ofthe mean annual flow volume
<br />(table 5; Bales and Robbins, 1995).
<br />Freshwater inflow to the Neuse
<br />River estuary (near site 47, fig. 7)
<br />was slightly less than inflow to
<br />the Pamlico River estuary, with
<br />
<br />W', " ,,' p " j -"f~~, '-'{'" ,'^ %,', ",,'
<br />Table 5. Estimated monthl{mean freshwater flow f[8m basiO~,.draining'to PamlicoSound,'N.C,. Se
<br />
<br />~\?ber 1999 p rI/,1" ~4
<br />[mi2~square miles; ft3is, cubic feet per second] M~, ,
<br />~ . M
<br />
<br />ill
<br />i@
<br />
<br />Basin
<br />
<br />"ft
<br />
<br />Chowan m:-'-
<br />Other drainage to Albemarle Sound
<br />Rainfall on the surface of Albemarle Sound
<br />Sub'tQtal forAJbemarle'Sound subba~!u
<br />Neuse
<br />Tar.Pamlico
<br />Other drainage to Pamtico Sound ~
<br />Rainfall ori the surface ofPamlico Sound
<br />TQ'rM.'"
<br />
<br />,. '~.. ...,
<br />
<br />Drainage art8
<br />(mil)
<br />t, (percentage
<br />ortotal$
<br />l' Pamlico Sound
<br />" 'ill'"
<br />.<>> drainag~r' ~
<br />~1i :& ~ #/'/. %
<br />
<br />W:September 1999
<br />Inflow volume ;".
<br />
<br />a,a
<br />percentag~ of
<br />Pamlico Sound
<br />~."'olurne:
<br />'j:;8ctual [normal!
<br />
<br />Two Months of Flooding in Eastern North Carolina, September-October ]999
<br />
<br />"ilL'" "0 b 19AA"-'~"
<br />&'X< ,,""~ \1. eto er _77YH(Mff/#K
<br />WI~ '" ':-, In, fto",/vO.lli~e,
<br />~ . '0 6,_ft;/ta':~~
<br />thlv {" - W/H.",,)^,.~S'?{!f.?.'f: ,
<br />---,,';_": p~:rce!1tage'_of_ *';
<br />flow "''''''''x,{ -'-;-;'i'hs--
<br />.""w PamlicoSOund
<br />Isr,",' ~'>;?"?.o-!iF-'!,uffi...~_
<br />~k'<'} volurne:lw%<<
<br />I actuallnoil1i~lI
<br />
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