A WATER QUALITY STUDY OF THE ELIZABETH RIVER:
THE EFFECTS OF THE ARMY BASE AND LAMRERT POINT STP EFFLUENTS
by Bruce J. Neilson
Special Report No, 75 in Applied Marine Science and Ocean Engineering
A Report to Hayes, Seay, Mattern and Yattern
Virginia Institute of Marine Science Gloucester Point, Virginia 23062
William J. Hargis, Jr. Director
May 1975 TABLE OF CONTENTS
Page Chapter 1. Conclusions and Recommendations ...... 1 Chapt Chapter 3 . The Fate of Materials Discharged into the Elizabeth River System ...... 12 Chapter 4 . Water Quality in the Elizabeth River System ...... 44 Chapter 5 . Summary ...... 52 Chapter 6 . Acknowledgements ...... 54 Chapter 7 . References ...... 55 Appendix A . Hydrologic and Climatological Data ...... 56 Appendix B . Data on Sewage Treatment Plants Discharging to the Elizabeth River System ...... 66 Appendix C . Biological Surveys ...... 71 Appendix D . Data from Water Quality Surveys and Dye Studies ...... 83 Appendix E . Elizabeth River Model ...... 103 CHAPTER 1. CONCLUSIONS AND RECOMMENDATIONS
1) An analysis of the slack water data from 1974 indicates that when strong stratidication exists in Hampton Roads, there will be strong vertical stratification in the Elizabeth River system as well. For these conditions, a non-tidal circulation will be set up which will enhance the exchange of water between the Elizabeth River and Hampton Roads. Therefore, water quality conditions within the ~lizabethkill be improved by this additional flushing.
2) Although tidal currents in the Elizabeth River
system are weak and the maximum speeds are on the order of
0.5 knots (0.25 m/sec), mixing due to tides and other factors is not weak. In fact, the mixing mechanisms are suffi-
ciently strong to oqercome vertical and horizontal density differences, resulting in a well-mixed and nearly homo- geneous body of water which may reach from Craney Island to the Portsmouth Naval Shipyards, These conditions arise when the freshwater flows to the James and the Elizabeth Rivers are low and stratification in Hampton Roads is moderate to weak. This can occur anytime during the year. 3) When the Elizabeth River is well-mixed, the non-tidal circulation is very weak or non-existent. Con- sequently residence times are quite large. The time re-
------quired for the system to reduce the amount of an injected substance to 10% of the initial amount for the September 1973 hydrographic conditions varies from 13 days for sub- stances introduced near Craney Island to 40 days for sub- stances released in the upper reaches of the Southern Branch.
4) Water temperatures, especially in the Southern
Branch, are elevated due to thermal discharges from power generating stations. Values between 25O and 30° centigrade have been measured in September 1973. It is believed that these high temperatures, in combination with the long residence time, cause a significant portion of the oxygen demand of waste waters to be exerted within the Elizabeth River System.
5) Field surveys have found violations of the current dissolved oxygen standards during several months of the year, primarily the summer months, and over several miles of the river. 6) Since the assimilation capacity of the river
is limited by physical factors beyond man's control, the only remaining method to maintain water quality standards
is to reduce the loadings of oxygen demanding substances tothesystem and/or to move the p~int~njectioncloser
to the river mouth. Unfortunately, some sources are difficult to control (e.g. non-point sources and urban
runoff) and advanced treatment is expensive. The dis-
persion and residence times are such that a change in the location of the Lambert Point outfall within the
Elizabeth River system (e.g. discharge near the present Army Base outfall) is expected to produce only a very
modest improvement in water quality. Therefore, it is
believed that DO violations will continue to occur until
the total input of oxygen demanding substances is greatly reduced.
7) At this time it is not possible to assess
the effects of moving the Army Base and Lambert Point out- falls into Hampton Roads with any certainty, since the
characteristics of the circulation there are not well-known,
It is believed that the water which leaves the Elizabeth River during ebb tide tends to retain its identity and,
to a great extent, returns on the subsequent flood tide,
If this is true, then the discharge point would have to be located either well into the natural channel at a depth
of 20 feet or more or at or beyond Sewell's Point before the
water quality in the Elizabeth River was improved significantly. CHAPTER 2. INTRODUCTION
In the past decades the Hampton Roads metropolitan region has experienced rapid population growth and industrial development. The Norfolk-Portsmouth portion of that region, which includes slightly over two-thirds of the population of the total area, is centered on the Elizabeth River system. This river receives the waste products which normally are generated by industrial and population centers: domestic waste waters, thermal discharges, and wastes generated by industry, shipbuilding and shipping. As a result, the Elizabeth is "an example of an excessively utilized waterway in regard to waste assimilation" (Pheiffer, et al., 1972). Two large municipal sewage treatment plants (STPss), the so-called Army Base and Lambert Point plants of the Hampton Roads Sanitation District, discharge 14 and 25 million gallons per day (MGD; 0.6 and 1.1 cubic meters per second) of treated waters respectively to the Elizabeth River system. The present study was undertaken to investigate the means by which and the rates at which materials discharged into the Elizabeth River are dispersed through and flushed out of the system. The primary focus of this exercise was to determine whether the existing outfall sites for the two STP's were so situated to minimize effects on water quality and if this were not the case, to note superior sites. The Elizabeth River System
The Elizabeth River system is comprised of the main stem of the Elizabeth (from Sewell's Point to Town
Point), the Lafayette River and the Western, Eastern and
Sazkh-Bra~~&s-ass kewni;n4%gur c3 1. T-fleELiz-afxrth is
part of the Intracoastal Waterway maintained by the Corps
of Engineers. At the head of the Southern Branch the
Waterway bifurcates, providing two inland routes between
Chesapeake Bay and Albermarle Sound. One route passes
through Great Bridge along the Chesapeake and Albemarle
Canal, down the North Landing River and into Currituck
Sound. The locks at Great Bridge control the flow of water
and mark the point where the tidal waves from the two
water bodies meet. Since both halves of the Waterway are
tidal, it bas been stated that there is no net flow through
the locks, and therefore that this waterway does not con-
tribute any freshwater to the Elizabeth River system
(Corps of Engineers, 1974). However, it is possible to
have a net flow if certain relationships exist between the
tidal phases and amplitudes on the two sides of the locks.
It also must be noted that water level fluctuations in
Currituck Sound are dominated by the wind rather than the
astronomical tides. Therefore, there very well could be
a net flow into or out of the Elizabeth River system, but
to this date, no measurements have been made by the Corps
or other agencies which would allow this flow to be estimated Western Branch
Southern Branch
Great Bridge STP
Figure 1. The Elizabeth River Syskem. or calculated. For this study the flow from the Chesapeake and Albermarle Canal has been assumed to be zero.
The second route follows the Dismal Swamp Canal and provides access to Albemarle Sound near Elizabeth
City, North Carolina. From an hydraulic poin_ttoffviewW,- the Dismal Swamp represents the high point of this region and water flows away from Lake Drumrnond in nearly every direction. The flow to the Southern Branch of the Elizabeth
River is controlled by the locks and spillway at Deep Creek.
This flow of water is the only natural Source of water which has been measured over the years. The long-term average monthly flows and the monthly flows for recent years ake gkven in Figure A-1 and Table A-2 in Appendix A. The long- term yearly average flow through the locks and spillway is 3 2309 million gallons per month (8,740,000 m /month) or 77 3 MGD (3.4 m /sec). During most of the year, the major portion of the flow enters via the spillway. ~uringthe dry part of the year, late summer and early fall, the flow is con- trolled by the lockages which increase due to use of the
Intracoastal Waterway by small craft.
Since the entire drainage basin for the Elizabeth
River lies very close to the Atlantic Ocean and entirely within the Coastal Plain provinces, the topographic relief is slight. The maximum natural elevation is on the order of
25 feet above mean sea level. The total area of the drainage basin is around 300 square miles. Urbanization normally increases the portion of rainfall that goes directly into overland runoff and reduces the portion which soaks into the ground and enters the groundwater supply, since large
areas are paved or otherwise covered with impervious mater-
ials. These three factors, low relief, small drainage a-r-Lu-,-z&lwaz~~~
groundwater flow into the Elizabeth and to increase the magnitude of the peak flows during rainy periods. Thus
the freshwater input from the tributaries is low during dry periods and has high peaks during wet periods. Since there
are no gaging stations on any of these tributaries, this
description remains an estimate of how the system works
and may not always hold true.
The third source of freshwater to the Elizabeth is
the large number of effluent streams from the sewage treat-
ment plants in the area. The loadings for the six HRSD
plants and the City of Portsmouth's Pinner Point plant are
given in Table B-1 in Appendix B. The combined flows of
these municipal STP's alone are in excess of 50 MGD (2.2
m 3 /sec), and industry contributes additional flows. It is
apparent that these flows are of the same order of magnitude
as the flow from the Dismal Swamp, and therefore must be
considered in the analysis of circulation,
Available Data
Although the Elizabeth River provides facilities
for commercial shipping and shipbuilding and is home port
for a sizeable portion of the U, S. naval fleet, much less
information on the system is available than one would expect. 9
Comprehensive studies of the entire system have not been reported in the literature. A large number of studies with limited goals have been conducted, and from these one can piece together a rough picture of the total system. -Fnr e~a~fhPit~~i~
the near field effects of the various outfalls and long term background data on the final plant effluents and water quality in the immediate vicinity of the outfalls. However, since no samples are collected at intermediate points or at "control stations", it is impossible to relate
the STP inputs to estuarine water quality in any quanti- tative fashion. Thus the usefulness of these data for
the purposes of this study is nil.
In 1972 a field study was conducted under the joint sponsorship of the James River "3-c" Study, HRSD, and the Cooperating State Agencies program between VIMS,
the State Water Control Board and the Division of Water
Resources. Dye was injected into the river system via the Lambert Point outfall for several days in April. This study provided the first concrete evidence that the effluent
from the Lambert Point plant was dispersed over a large
area including reaches several miles upriver from the
outfall. It was also found that the system had not reached equilibrium conditions during the study so that one recommen- dation for future studies was that dye be injected at a
slower rate over a longer period of time. 10 In 1973 a program was initiated at the Virginia
Institute of Marine Science (VIMS) which was sponsored by the National Science Foundation's Research Applied to
National Needs (RANN) program. The three primary elements of this study were: 1) Regular slack water monitoring of the system. 2) Intensive field surveys to follow the dispersion of dye throughout the system due to long term
(2 weeks) injection of dye via the Lambert Point STP outfall. These surveys were conducted in September of 1973 and May of 1974. 3) The development of a mathematical model of the Elizabeth River system. A data report, a description of the mathematical model and a summary of the water quality surveys will be released in the Spring of 1975.
A third intensive field survey was conducted for the present study in August of 1974. Dye was injected into the effluent of the Army Base STP at the downstream end of the chlorine contact chamber at the rate of 6 gallons per day for 15 days. On the last two days, nine stations along the Main Branch of the Elizabeth and in the Lafayette River and the Western Branch were sampled hourly for thirteen hours per day. In addition a moving boat traveled through the system monitoring surface dye concentrations near slack water. Parameters measured hourly at the anchor stations were temperature, salinity, dye, dissolved oxygen; bio- chemical oxygen demand also was measured at the end of the survey. Graphs, profiles and tabular summaries of these data which illustrate pertinent features of the system will be presented in the text. A presentation of data from the two RANN surveys and the Army Base study is included in Appendix D. CHAPTER 3. THE FATE OF MATERIALS DISCHARGED INTO THE ELIZABETH RIVER SYSTEM
A substance which is discharged to the waters of the Elizabeth River system will be dispersed, diluted and carried away by several physical processes, First, under most circumstances there will be dilution due to entrainment of ambient water in the effluent jet, Second, tidal currents will cause mixing, and this so-called
"tidal mixing" will tend to disperse materials and reduce concentration gradients. Third, there will be the advective flow due to the freshwater inflows at the heads of the several tributaries. This flow tends to transport wastes through the system and out into Hampton Roads. And fourth, there is the exchange of waters between the Elizabeth River and Hampton Roads. One component of this exchange is due to the tides and the circulation pattern in Hampton Roads which bring "new" water into the Elizabeth on every flood tide. This component will vary somewhat as the amplitude of the tide varies from spring tide to neap tide. The other component is non-tidal in nature and is caused by density induced circulation. For partially stratified estuaries, there is a net upriver flow of salty water near the bottom of the river and a net downriver flow of fresher water near the surface. The strength of this non-tidal circulation is a function of the density gradients which are caused primarily by variations in salinity. The salinity regime in turn is dependent on the history of freshwater runoff. Since all of these processes act upon the system at one
time it is difficult to separate out the effects of each
individual process. However, comparison of the slack water data for the summer of 1974 will illustrate some
aspects of how the system works.
Slack Water Surveys, 1974
In addition to the intensive surveys, a series of
regular slack water runs was made during the summer of
1974 at approximately two week intervals. The slack tide wave in the Elizabeth is similar to a standing wave, with
slack water occurring nearly simultaneously throughout
the whole system. Consequently, it is very difficult to
take all samples precisely at slack water, Furthermore,
it is impossible for one boat to survey more than the main
stem and one of the tributaries within the period of weak
currents. Normally, the main stem and the Southern Branch
were sampled on each run and one or more of the other
tributaries sampled prior to or after slack water, The
data which will be presented are for the main stem and the
Southern Branch.
During the month of April 1974 the rainfall for
the Norfolk area was 3.34 inches. About two thirds of this
occurred in the first ten days of the month, Rainfall for
the entire James River Basin apparently followed the same
pattern, since river flow at ~ichmondrose to a maximum
of 27,000 cfs (759 m"/secj on the 7th, and decreased steadily 14 thereafter. For purposes of comparison, the long term average flow at Richmond is about 7200 cfs (200 m3/sec).
The flow for the last half of the month was between 5,000 and 10,000 cfs (150 to 300 m 3/sec). The flow from the
208 MGD (9 m3/sec), nearly twice the long term average flow for April. One could assume that this flow also was high in the first half of the month and decreased during the latter half. For these conditions, there was moderate vertical salinity stratification within the Elizabeth with two ppt (parts per thousand) surface to bottom difference at most stations. At the mouth, near Craney Island the vertical difference was greater and on the order of 5 ppt,
Surface salinities varied from around 17 at Craney Island
(Station Al) to 13 ppt at the Interstate Highway bridge
(Station E3). Thus it appears that for moderate freshwater flows in the Elizabeth and the James, there will be moderate vertical stratification in the Elizabeth and also a moderate longitudinal salinity gradient. These conditions are illustrated by the data for May 1 and 2, 1974 as shown in
Figures 2 and 3.
During the first half of May, rainfall at Norfolk for the first 17 days amounted to 1.7 inches. Conditions for the James were quite different, and flow at Richmond 3 reached a peak of nearly 37,000 cfs (lo00 m /set) on the
15th. The flow was over 10,000 cfs (300 m3/sec) from the
12th to the 20th inclusive. This resulted in greater Eastern Branch
Branch
Stations A1 A2 B1 C2 C3 Dl El E2 E3
Stations A1 A2 B1 C2 C3 Dl E1 E2 E3 0 - 2 - 4 - A % 6- : 8- - 10- 5 12- a a Q 14- 16- Salinity (ppt) 18 - May 2, 1974 Low Water Slack
Figures 2 and 3. Low water slack salinity profiles. 16 vertical stratification in Hampton Roads as the upper
layer of water was diluted and freshened by the seaward
flowing rainwaters. On the 17th of May the salinity at
the surface near Craney Island was down to around 12 ppt, and the surface to bottom difference had increased from
6 ppt to 13 parts per thousand. This resulted in greater vertical stratification within the Elizabeth River as well; the vertical difference at most stations was nearly
6 ppt. The isohalines, or lines of constant salinity,
are nearly horizontal whereas those for the 1st and 2nd
of May were much more vertically inclined. (See Figure 4).
During the period May 17 to June 5, the rainfall
at Norfolk was 2.56 inches, the river flow at Richmond was 3 at or above 5,000 cfs (150 m /sec), and the monthly flow
from the Dismal Swamp was 720 million gallons or 24 MGD 3 (1 m /set), roughly half of the long term average discharge.
As a result of these reduced freshwater inflows, vertical
and horizontal salinity gradients were greatly reduced as
can be seen in Figure 5. Because of the salt intrusion in
mid-May, salinity levels were generally higher on June 5
than on May 1 or 2. Although the flow at Richmond peaked
to more than 20,000 cfs (600 m5/sec) on June 5, there was
no downstream impact at that time. The surface to bottom
difference at Craney Island was less than 3 ppt and the
central reach of the Elizabeth from Lambert Point to the
Portsmouth Naval Yards (stations B1 to El) was nearly
homogeneous. Thus we can see that during periods of Low Stations A A0 A1 A2 B1 C2 C3 Dl El E2 E3
Figure 4. Low water slaclc salinity profile.
Stations A A0 A1 A2 B1 C2 C3 Dl El E2 E3 I I I
Salinity (ppt) June 5, 1974 High Water Slack
Figure 5. High water slack salinity profile. 18 freshwater flow and moderate stratification in Harnpton
Roads, tidal mixing reduces vertical and longitudinal gradients and the river tends towards well-mixed conditions.
Vertical and horizontal variations are not completely eliminated, but the gradients are slight everywhere except near the boundaries.
For the period June 5 to 27, 1974 there were 3-59 inches of rain at Norfolk, and nearly all of this occurred on the 20th, 22nd, and 23rd. The James River flow at 3 Richmond was normally less than 5,000 cfs (150 m /set) and
the monthly flow from the Dismal Swamp was 98Q million gallons or 32 MGD (1.4 m5/sec) , about 30% greater than the long term average for June. For this period then, the only
large input of freshwater was the rain several days before
the slack water survey. A comparison of the salinity profiles in Figures 5 and 6 shows that the isohalines have become more horizontal and that the upstream salinity has
been reduced from 15 ppt to 12 ppt. Downstream conditions
in Hampton Roads on the other hand have remained nearly
constant. A surface to bottom salinity difference of two
ppt can be found throughout most of the Elizabeth.
The month of July was in general dry, and the river 3 flow at Richmond was consistently below 5,000 cfs (150 m /sec) . The rainfall at Norfolk between June 27 and July 31 was
6.06 inches; however, 3.81 inches fell on July 26 and 1.01
inches on July 30. As a result of this large freshwater
inflow, on July 3 the vertical stratification in the Elizabeth Stations A A0 A1 A2 B1 C2 C3 Dl E1 E2 E3
Stations A A0 A1 A2 B1 C2 C3 Dl El E 2 E 3
Figures 6 and 7. Low water slack salinity profiles. was strong as seen in Figure 7. The isohalines are nearly horizontal and surface to bottom salinity differences of
6 ppt can be observed for most stations. Stratification
in Hampton Roads and the longitudinal gradient in the upper Southern Branch also increased.
During August, the flow at Richmond continued to 3 be below 5,000 cfs (150 m /sec) most of the time; the dis-
charge from the Dismal Swamp was 1230 million gallons or 3 40 MGD (1.7 m /sec) above average for August; and the rain-
fall for the period July 31 to August 27 was 8.13 inches.
As a result of this high local rainfall, stratification was rather strong within the Elizabeth River and in Hampton
Roads, as shown in Figure 8. Surface to bottom salinity
differences of 6 ppt were typical. Isohalines were
essentially horizontal.
In summary, it appears that tidal mixing and the
salinity stratification in Hampton Roads are the controlling
variables which determine the salinity structure in the
Elizabeth. Contrary to published reports that the Elizabeth
has "sluggish tidal cycles" and "low dispersion and transport
characteristics" (Pheif fer, et a1, , 1972) , the data gathered during the recent studies indicate that mixing in the
Elizabeth is not weak. In addition to tides, winds and
the constant passage of tugs, commercial freighters and
naval ships contribute to the mixing process. Furthermore,
the tidal component probably varies, being strongest at Stations
Salinity (ppt) August 27, 1974 Low Water Slack
Stations A1 A2 B1 C2 C3 Dl El E 2 E 3
Salinity (ppt) September 21, 1973 Low Water Slack
Figures 8 and 9. Low water slack salinity profiles, 22 spring tide and weakest at neap tide. Since there is no method to differentiate the various mixing processes, their net combined effect has been called "tidal mixing". The important point is that this mixing process is sufficiently
gradients. Two periods when these "well-mixed" conditions occurred in the Elizabeth are September 1973 and March 1974.
Rainfall at the Norfolk airport was 0.62 inches for the first
21 days of September and 3.59 inches for the first 27 days of March. For both surveys, the central portion of the river was essentially homogeneous as can be seen in Figures 9 and
10. In September, the upper reaches of the Southern Branch were sectionally homogeneous, that is vertical differences were slight although there remained a moderate horizontal gradient, whereas in March both vertical and longitudinal gradients were observed. For both cases it appears that the surface to bottom salinity difference in Hampton Roads was less than 5 parts per thousand. Apparently, the mixing pro- cess is more complete in the Elizabeth than in Hampton Roads,
In contrast to periods when much of the Elizabeth is homogeneous, there are periods of strong vertical stratifi- cation. It appears that anytime there is strong stratifi- cation in Hampton Roads, the Elizabeth will also exhibit similar conditions. At present the data are insufficient to determine with any precision what river flows will cause this to happen. On a qualitative basis, though, it appears that localized rainfalls of moderate intensity within the Stations A A0 A1 A2 B1 C2 C3 Dl El E2 E3
Figure 10. High water slack salinity profile. Elizabeth River drainage basin will increase stratification only slightly. The strong stratification in Hampton Roads can be caused by sharp increases in the freshwater flow
May 15, 1974) heavy rainfall in the entire Harnpton Roads area, or extremely intense storms in any of the small drainage basins tributary to Hampton Roads. Since meteorological data are collected at only a very few points, one cannot distinguish between very localized summer thunder showers and larger, regional patterns of rain. Neither are there any gaging stations on the higher order streams. Nonetheless, the important point to be gotten from this discussion is that strong stratification in Hampton Roads, no matter what causes it, will extend into the Elizabeth River. Since the naviga- tion channel in the Elizabeth is 35qeep to the turning basin near Newton Creek, river mile 15.5, the wedge of salty water can move far upstream. For example, on May 17, 1974,
Figure 4, one can note that the isohalines are nearly hori-
zontal not only in the downstream reaches but also at station
E3, the most upriver station at mile 16.5, indicating that even the reaches near Great Bridge can be affected by this type of salinity stratification.
The two situations just described represent the extreme cases between which conditions range, Typically there will be both vertical and longitudinal variations of salinity within the Elizabeth, but the gradient will not be strong. 25 The final point to note from this discussion is that there is a non-tidal circulation of water between Hampton Roads and the Elizabeth River. During periods of strong stratifi- cation, there will be a very substantial net non-tidal flow of saltier water into the Elizabeth near the bottom and fresher water out to Hampton Roads near the surface. During periods of homogeneous or well-mixed conditions, this non- tidal flow will not exist. Therefore, the flushing of the
Elizabeth will be poorest during these periods and the residence time of water in the Elizabeth will be great.
Residence Time In the previous section it was shown that tidal mixing tends to reduce both vertical and horizontal salinity gradients, and therefore tidal mixing can be expected to reduce the gradients of other water constituents. In particular STP effluents will tend to be dispersed in the system by the action of the tides. It was also noted that the exchange of water between the Elizabeth and Hampton Roads will depend on tides and also the non-tidal circulation that is set up by density gradients. During periods of low freshwater inflow and moderate stratification in Hampton Roads, we can expect a relatively homogeneous water mass to exist in the
Elizabeth River sys tern. During these times, the non-tidal circulation will be very weak or nonexistent and flushing will be reduced. This represents the "worst case conditions" for the physical system. Consequently, the analysis of resi- dence time will focus on the conditions which existed during 26 September 1973, when homogeneity occurred over a large portion of the river.
The time that a substance resides in the system also will be a function of the location at which the sub- stance is introduced into the system. For example, the rate of dye injection for the Army Base Study was 1.5 times that used at the Lambert Point plant. However, the Army Base plant is closer to the mouth of the Elizabeth River. Also during September 1973, the Elizabeth was well-mixed while during August 1974 there was rather strong stratification.
As a result, the actual dye concentration levels were lower in August 1974 than in September 1973, as shown in Figures
11 and 12.
A quantitative method to illustrate the residence time and how it varies is to run the mathematical model to simulate the dispersion and flushing of a conservative sub- stance. The model is a branched, one-dimensional tidal average model. Variations within the tidal cycle are not included, so that the results are presented in terms of days rather than number to tidal cycles. A more complete description of the model, examples of input data and the results of the verification runs for September 1973 con- ditions are included in Appendix E.
The conditions which existed in September of 1973 are close to "worst case" conditions, so these were used for the tests. For each test an arbitrary concentration level was assumed to exist within a given reach. The reaches are Stations
Stations A1 A2 B1 C2 C3. Dl. El E2
------1 10 Dye (PP~) 15 20 2o September 20, 1973 Low Water Slack
Figures 11 and 12. Low water slack salinity profiles. shown in Figure 1, and the numbering begins with 1 at Great Bridge and continues to 17 near Craney Island. The results of each model run include the concentration in each reach and, on each day for which the results were printed out. The concentrations for the Main and Southern Branches of the
Elizabeth have been plotted in Figures 13 to 16 for a sequence of days after the initial release, and for releases in segment
6 (Washington STP) , 10 (Portsmouth shipyards), 15 (Lambert Point STP) , and 17 (Army Base STP) . In these figures, we can observe the effects of the two processes which have been described in the preceding sections, namely dispersion due to tidal mixing and flushing or removal due to tidal exchange with Hampton Roads, In Figure 13, one can see that for several days after the release of material to segment 6, almost no material is lost from the system since the concentrations in segment 17 are very small and more than four orders of magnitude smaller than the initial concentration. After 4 days, there remains more than two orders of magnitude difference between the concentra- tions in segments 6 and 17. But after 11 days, the concen- trations are rather uniform spatially and the difference is roughly one order of magnitude. At the other end of the river, a release to segment 17, as shown in Figure 16, moves upriver even more slowly since the concentrations in segments
2 and 3 are more than three orders of magnitude smaller than the initial concentration four days after the release. At later times, not only are the upstream concentrations of Segment Number
Figure 13. Concentration distributions on several days after release to segment 6. Segment Number Figure 14. Concentration distributions on several days after release to segment 10. Figure 15. Concentration distributions on several days after release to segment 15. 0 0 Days j
Segment Number
Figure 16. Concentration distributions on several days after release to segment 17, the same order of magnitude as the downstream levels, but also the location of the peak concentration has moved upriver. The release to segment 10, as shown in Figure
14, moves both upriver and downriver.
eneral, one can see that in-the immediate vicinity of the release, the concentrations decrease after the first day. Far from the release point, the concentra- tions increase for roughly two weeks and then decrease thereafter. After about ten days, the concentrations are usually relatively uniform spatially with the extreme concen- trations differing by about one order of magnitude.
The changes in concentrations illustrate how material disperses through the system and show that the tidal exchange with Hampton Roads is the primary mechanism which removes material from the Elizabeth. The reaches have quite different volumes, and of course some of the material enters the tributaries. The most quantiative method to show residence time is to plot the amount remaining in the system as a function of time. The initial concentrations were chosen so that the amount of the substance released to the river was 1,000 (arbitrary units) . The products of the volumes and concentrations for each reach were calculated and summed to find the amount remaining in the system on each day tested. These die-off curves are shown in Figure 17 for releases in segments 6, 10, 13, 15, and 17. The results are summarized in Table 1. Q Segment 6 - Wash. STP 0 Segment 7/10 a Segment 1/13 Segment 7/15 - Lambert Point STP @ Segment 7/17 - Army Base STP
Time (Days)
Figure 17. Residence time as illustrated by remaining portion of substance injected at various locations. ah, rd N -4 fi r-i +' W m h a, m A c, G .ri a, tn ki G a, .rl 1( r-i G =a' m o C9 -rl m cv cv r-i 0 cd +' 8 d p: rd - ,+ a, k m a, rd c, a, d 9 2 k 0 'i-4 '+I 0
Ln LO m t"- . r-i -4' d
. r-i 36 There is no single definition of residence time which is universally used and understood. Rather there are several similar and related definitions all of which are based on a linear decay or removal rate, but which give dif-f-erent answers. The first definition probably comes from nuclear science, where the "half-life" of a substance is calculated. This definition of the residence time is the time required for the amount of a substance in the system to be reduced by a half. For an estuary like the Elizabeth, this definition is probably not a good one since the removal from the system depends on both dispersion and tidal exchange.
Material discharged into segment 17, the most downriver seg- ment, of course was lost beginning the first day. Material discharged into segments far upstream, such as segment 6, had to be dispersed through the system before there was any significant removal by tidal exchange. The half-life defin- ition of residence time over-emphasizes the initial period so that long term predictions are inaccurate. For example, after around three and a third "half-lives", 10% of the total amount should remain in the system. If the numbers in the 0.5 column of Table 1 are multiplied by 3.3, the products do not resemble the numbers in the 0.1 column. For upstream segments, the half-life definition predicts overly long residence times, and for the downstream reaches it under- estimates the residence time.
A second definition has statistical origins, and the residence time is defined as the mean of the times the individual parcels of water spend in the system. The concen- tration at this mean residence time is the inverse of "en, the natural or Naperian base, or 0.37. If around two and a third of these cycles occur then the remaining concentration should again be 0.1. If the numbers in the 0.37 column of
Table 1 are multiplied by 2.3, the products are fairly close to those in the 0.1 column, but again the estimates are too large for upstream and too small for downstream reaches.
A third definition of residence time is the time required for the amount to be reduced to a tenth of the original value. If the curves are extended to the 1%level, and if the 10% residence time is doubled, one again observes that values upstream are overestimated and values down- stream are underestimated. Since the flushing of material from the Elizabeth involves two processes, dispersion and tidal exchange, no simple measure of residence time will give good predictions when it is projected over a long time frame.
The best definition for the Elizabeth is the 10% residence time, since this definitely reduces the time lag effects of dispersion and since an order of magnitude reduction is substantial. Howeveri it should be noted that the results agree in general no matter which definition is used.
The important points to note are that the residence times increase rapidly as the injection point is moved upriver and that the residence times are always quite large. This means that a large portion of the carbonaceous biochemical oxygen demand (C-BOD) is exerted within the system. For materials released at upriver points it could well be that most of the C-BOD and a substantial portion of the nitrogenous
BOD (N-BOD) are exerted before the material leaves the Elizabeth River.
hese results are for something approaching "worst case" conditions, but not extreme or unreasonable conditions. Residence times will be smaller when there is greater runoff into the tributaries and greater stratification in Hampton
Roads. However, since tidal mixing is great in the Elizabeth, materials will tend to be dispersed throughout the system for much of the year.
Bui ld-up
The study of flushing rates and die-off provides information on the manner in which instantaneous or "batch" releases will be dispersed and removed from the system. Although this type of release occurs frequently, especially for certain types of industrial processes, the more common form of release is the continuous discharge. Municipal
STP's, for example, normally discharge continuously, although there will be diurnal and seasonal variations in the quantity and the quality of the waste water stream. For large systems, the hydraulic characteristics of the sewer system will tend to mitigate these variations. For the purposes of this study, we will assume that the effluent streams from the Army Base and Lambert Point plants are constant in flow rate and water characteristics. From a theoretical point of view, the long term build-up curves can be gotten from the die-off curves. Each day there will be a distribution due to that day% discharge, and the amount of the substance injected into the system will be dispersed and flushed-out of the system as described in the previous section. However, on each subsequent day, there will be additional discharges, Normally one uses the assumption that the effects can be added in a linear fashion in order to determine the combined effects. If no other method were available, this would be a satisfactory albeit time consuming approach to the problem. For this study, the math model was used to simulate continuous discharge into segments 17 (Army Base) and 15 (Lambert Point). The results of these two runs are shown graphically in Figures 18, 19 and 20.
In the preceding section it was noted that it takes several days for an effluent to disperse into the farther reaches of the river. One can note in Figures 18
& 19 that for both release points, the concentrations in segments 2 and 3 were more than two orders of magnitude smaller than the downstream concentrations even after five days. By the 10th day, the effects were felt throughout the river, and by the 20th day, the system was beginning to approach equilibrium levels. The release rate was 10,000 cfs x mg/R or 54,000 pounds per day. The equilibrium concentrations for the release from the Army Base plant were in the range 50 to 100 mg/R for most of the river and in Segment Number Figure 18. Buildup of concentration distribution due to a continuous release to segment 17. 1 Segment 15 n Day (Lambert Point) : 2 6.) 5
Segment Number
Figure 19. Buildup of concentration distributions due to a continuous release to Segment 15. the range 100 to 175 mg/R for the Lambert Point plant,
In general, the variation in concentration from reach
to reach was slight except near the upstream or downstream
After a certain period of time, the system will
reach equilibrium; that is, the amount lost from the system
during a day will just equal the amount discharged to the
system, assuming that the discharge rate is constant. In
Figure 20, the amount of material in the system is plotted
as a function of time. One can note very rapid build up
in the first ten days, with a much more gradual increase
thereafter. After a period of a month or more, the equil-
ibrium levels are approached. Roughly seven times the daily
loading from the Lambert Point plant remains in the system
in contrast to only five times the daily loading from the
Army Base plant. Since the Lambert Point discharges around
20,000 pounds of BOD5 each day, it is obvious that a large
amount of oxygen demanding material remains within the
Elizabeth River system under equilibrium conditions. The
model runs were made with the September 1973 hydrographic
conditions. For periods when stratification is present,
flushing will be increased and the equilibrium levels will
be reduced. BUILD-UP
INPUT 10,000 units/day
Days
Figure 20. Buildup of the amount in the system due to continuous release to segments 15 and 17. CHAPTER 4. WATER QUALITY IN THE ELIZABETH RIVER SYSTEM
The BOD levels which have been measured in the Elizabeth
River system are quite low. Values greater than 5 mg/R
p--~~---~~~-~------p------were normally found only at the surface and near the STP
outfalls. On several occasions most of the 5-day BOD
values for the river were on the order of 1 or 2 mg/R.
This is not unreasonable since the volume of water available
for dilution is great. If the total daily input of BOD
(50,000 lbs.) were uniformly dispersed in the mean low
water volume (176 x lo6 meter3), the resulting concentration would be only 0.125 mg/~.
Water temperatures in the Elizabeth vary greatly
with location and season. The water near the mouth tends
to have temperatures equal to those found in Hampton
Roads. For the Southern Branch, however, water temperatures
are normally several degrees higher due to the thermal
discharges of the power plant located there, During the
summer, water temperatures in the Southern Branch are
often above 250C and on at least one occasion, the surface
temperatures near the Interstate Highway Bridge were great-
er than 320C, the maximum value on the recording instrument.
Despite the low BOD levels, dissolved oxygen levels
during much of the year are below water quality standards.
During 1974, DO concentrations below 4 mg/l were found on
every slack water run from April on, The DO concentrations
for low and high water slack during the Army Base survey 45 are shown in Figures 21 and 22. One possible explanation is that the long residence time and the high temperatures in combination cause a large portion of the oxygen demand to be exerted in the ~lizabethRiver system. Furthermore, it appear-s that the reaera-tion capacity-of the river is limited.
Although tidal mixing (including wind and other factors) is great, tidal currents are not strong. The maximum currents during flood and ebb tides which are predicted for average tides in the Tidal Current Tables range from 0.3 to 0.7 knots
(0.15 to 0.36 meters per second) for the entire river, with the exception of ebb tide near Craney Island. Consequently natural reaeration is not great. Furthermore, in some reaches the average depths are large since most of the cross-section is included in dredged channels and berthing areas. For these reaches, the available oxygen must be dispersed through a rather deep water column, further limiting the ambient DO levels. In fact, the reach of the river near the Portsmouth
Naval Shipyards, which has an average depth of about 10 meters, consistently shows up in both slack water runs and in the mathematical model predictions as an area with very low DO concentrations. As noted in the following section, the observed levels of chlorophyll "a" were not high, so that the results of this study do not show algal blooms to be a major factor in the substandard DO levels. No algal blooms were noted during the course of this study.
Water samples also were collected and analyzed for chlorophyll "a", once during the summer of 1974. The 4 6
Stations A2 B1 C2 C3
Stations
Figures 21 and 22. Dissolved oxygen profiles for high and low water slacks. level of chlorophyll "a" at the Deep Creek locks was 3.1 pg/R (micrograms per liter). Values for the Southern Branch and the Elizabeth were in the range 10.0 to 12.5 vg/R. A sample from the Lafayette River had the highest reading of
32.7 pg/R. One interpretation of these figures is that chlorophyll levels in the water coming from the Dismal Swamp are low. Due to dispersion, the levels in the Southern Branch and main stem of the Elizabeth are rather uniform and higher, but certainly well below the levels recommended by EPA for the Potomac Estuary. The levels in the Lafayette River are high probably because the tidal currents are weak (allowing plankton to remain near the surface) and the water is shallow
(placing most of the water in the photic zone).
Benthic surveys (Boesch, 1971 and Richardson, 1971) showed that the Elizabeth River was polluted relative to
Hampton Roads and the Chesapeake Bay regions. Since no gen- erally accepted measures of the environmental effects exist, it is not possible to quantify these differences at this time.
The summaries from these surveys are included in Appendix C.
Analyses of sediment samples taken from the Eliza- beth River Channel (VIMS, 1972) showed high levels of both nutrients and heavy metals, as can be seen in Figures 23 and
24. A variety of inputs come from urban runoff, shipbuilding activities, industry, domestic sewage treatment plants and so on. At present the data are insufficient to pinpoint the major contributors of the various constituents. One can note high peak concentrations for a few elements, e.g, lead at about river mile 10, which would appear to indicate a point source. In general however, the levels are rather uniform, supporting the conclusion of strong tidal dispersion. MILES FROM MOUTH
Figure 23a. Heavy metal concentrations in sediments, (From VIMS, 1972) .
Figure 24. Nutrient concentrations in sediments. (From VIMS, 1972). CHAPTER 5. SUMMARY
Water quality in the Elizabeth River system is controlled primarily by physical factors. During some periods of the year, there is strong stratification in
Hampton Roads which causes similar stratification in the
Elizabeth. During these periods, a non-tidal circulation will be set up by the density gradients and flushing will be enhanced. Thus one can anticipate relatively high quality water when stratification is present and strong. On the other hand, tidal mixing in the Elizabeth is great and this process tends to break down the stratification. When fresh- water flows in the James and the Elizabeth are low, completely mixed or homogeneous conditions can occur and have occurred in the Elizabeth. During these periods there will no non- tidal circulation and the exchange of water with Hampton
Roads will be due to the tidal excursion alone. The residence time is on the order of weeks for these conditions.
The Elizabeth receives the waste products of the
Norfolk metropolitan region, including waste heat and domestic sewage. When flushing is small and ambient temperatures are high, a large portion of the oxygen demand associated with the STP effluents can be exerted within the river system,
Field measurements during the past few years have shown that the current water quality standardsfor dissolved oxygen are violated several months of the year. Daily averages
are below 5 mg/R of DO for several miles of the river and
a few reaches experience DO'S well below the 4 mg/R minimum. Flushing is weak during periods when the water
column is homogeneous, and natural reaeration is limited due to weak tidal currents, so that the assimilation
capacity of the river is not great. Since control of flushing is not feasible, it would appear that the only
remaining method to meet water quality standards is to
reduce the waste loadings to the river. CHAPTER 6. ACKNOWLEDGEMENTS
The author gratefully acknowledges the financial support of the Hampton Roads Sanitation District and Hayes,
Robert Jennings of HSM&M is also appreciated.
The author also acknowledges the following persons for their contributions to this study: - Albert Kuo for the development of the Elizabeth River model;
- C. S. Fang for assistance in organizing the project; - John Jacobson for his assistance with field efforts; - Shirley Crossley for typing of manuscripts; - and the members of the Department of Physical Oceanography and Hydraulics for their discussions, comments and critiques, especially regarding the analysis of circulation patterns. CHAPTER 7, REFERENCES
Boesch, Donald F. "Distribution and Structure of
Benthic Communities in the Hampton Roads Area,
Virginia", Virginia Institute of Marine Science
SRAMSOE #15, April 1971.
Corps of Engineers, Norfolk District. Personal
Communication, 1974.
Pheiffer, Thomas H., Daniel K. Donnelly and Dorothy
A. Possehl, "Water Quality Conditions in the
Chesapeake Bay System", Technical Report 55, August,
1972, Annapolis Field Office, Environmental Protection
Agency, August 1972.
Richardson, Michael D. "Benthic Macro-invertebrate
Communities as Indicators of Pollution in the
Elizabeth River, Hampton Roads, Virginia", Masters
Thesis, Virginia Institute of Marine Science, 1971.
Tidal Current Tables, Coast & Geodetic Survey, U. S.
Department of Commerce. Issued Annually.
Virginia Institute of Marine Science. "Study of Channel Sediments, James River and Hampton Roads Area,"
Contract Report to the U.S. Army, Corps of
Engineers, 1972. Appendix A. Hydrologic and Climatological Data
Figure A-1. Average monthly flow from the Dismal Swamp Canal to the Southern Branch, Elizabeth River.
Table A-2. 1973 and1974 -Monthly flows from the Dismal Swamp and to the Southern Branch, Elizabeth River.
Figure A-3. Flow rate at Richmond, James River.
a) April and May 1974 b) June and July 1974 c) August and September 1974
Table A-4. Climatological Conditions, Norfolk Regional Airport, 1974.
a) April b) May c) June d) July e) August f) September
Table A-2. Flow from the Dismal Swamp Canal to the Southern Branch, Elizabeth River, in Million Gallons
1974 Average 1955-73
Lock Spillway Lock Spillway Lock Spillway January February March April May June July August September October November December
Yearly Average 119.3 2309
Yearly Average Total Flow = 2328 I U I 1 I 1 1 I -4 1'0 2'0 30 10 20 30 10 20 30 A 5 April May June U
t I 1 10 20 30 10 20 30 10 20 30 July Aug . Sept .
Figure A-3. Flow rate at Richmond, James River, 1974.
E1.5. OEPA2lFEI&T @? EGSSERCE HS2Fei.K IERIOXRI. bCRG'OVi- JOKE ER7fi PIBT~BREL ilcg~fiu~~o#a nrnespctmse nosr#rsr~~r~e~ 62 EMVKWOHREHZRB OWTW SERVICE
Appendix B. Data on Sewage Treatment Plants Discharging
to the Elizabeth River System
Table B-2. BOD Concentrations
Table B-3. BOD Loads
Table B-4. Suspended Solids Concentrations
+' a, rd rik 2 4z U
a a, [I) Table B-3
BOD Load in Pounds/Day
Certified Average (1973) Mon t 11y Range (1973)
Army Base (HRSD) 12,845 12,600 11 I 200 - 13,800
Lambert Point (HRSD) 23,350 23,500 211
Western Branch (HRSD) 2,335 1,880 1I
Pinner Point (City of Portsmouth)
Deep Creek (HRSD)
Washington (HRSD)
Great Bridge (HRSD)
* Based on July, August, November & December data only. Table B-4
Suspended Solids Concentration in pg/Q
Certified Average (1973) Monthly Range (1973)
Army Base (HRSD) 100 66 60 - 77
Lambert Point (HRSD) 100 71 60 - 82
Western Branch (HRSD) 100 74 54 - 100
Pinner Point (City of Portsmouth)
Deep Creek (HRSD)
Washington (HRSD)
Great Bridge (HRSD)
* Based on November and December data only. Appendix C - Biological Surveys
C-1. Master's Thesis, Michael D. Richardson, 1971
Figure C-1-a. Title Page Figure C-1-b. Abstract Figure C-1-c. Sampling Station Location Figure C-1-d. Summary
C-2. VIMS - SRAMSOE No, 15 - Donald Eoesch
Figure C-2-a. Title Page Figure C-2-b. Sampling Station Location Figure C-2-c. Summary BENTHIC E%CROIFvTRTEB=S CGVZ,'YCTIES AS
IITDICATOES OF P3LLUTIOTi IN TE5 ZLIZABEZ-I-
Rm, IiAb?TON ROk,3S, VIFGIIJU
A Thesis
Presented to
The Faculty of the School of Karine Science
The College of William a~dKar; in Virginia
In Fadial Fiilftllmer-=
Of the Requirezents fcr tke Zegree of
Easter of Srts The macrobenthos of the Elizabeth F.il:er, Fazipton Roads, Virginia, was sailed to defice com'i:nity str-dcture and to determine possible alteration of this cornunity because of pcllution. T'ne samples were doxtnated by polluticr; tole ran'^ organisrs w5de geographic ranges. These organisms are rarely dominant in oC,Fer com.~rmities, except under stress conditions.
Ken-selective de~ositfeeders $;ere fc~din 10iq x1w3bers because of tke lack of oxygeil and i3igh co~~centratiol?of hydrogen sulfide found in deposits below 1 Suspensioll feedezs and selective deposit feeders were favored kecause of the good supply cf well aerated de'trital material on the sediJnent s~~xfaeeand trzpped in abundant oyster shells,
The mean Ht diversity -value (2.96 birs/indiv. ) was as high as that in some unpolluted areas, becxse polk~~tion tolerant species maimained high equitability values. Species rlchess ~msreduced,
The benkhos was ~ostaffected. by polktion in tk'iay. Diversity and species richness valces were reduce2 and ~::e ratio of pollution tolerant to non-yol3ition toleranz organisrs increased.
1. Ib:acrobenthos in the Elizabeth River, liqton Roads, Virginia, were szmpled to define community structure and to determine tlie effects
of pollrrkio:~on co~mw:ity stzuc-hre. %~elvestatlens were saxpled by grabs d.;lr.irg three sqling periods in 1969.
ghty-seven grabs yielded 22,404 indiv',du?d-s divided among
122 ide~ltifiabletaxa. Of these, 76.4% were polj-ckaetes, 15.35 mollusks, 3.4; cmstacears, and 4.9% other taxa.
3. The samples had a man density of 3,803 individuals/ni2.
Den~lfyIZ"U:: higher zC, statiox located on dead oj-ster reefs, becacse of the iwrezsed zvailability of oxygenated detrital naterial and the preseLce of a substrate for attachment,
k. The sitzples were domizlated by TJereis -- x~tero~nia~tx~ ocv2: *--;s 22.l?2? 13 ____l-.
FZ-?~--7- -,--c7,= - G..- Lb---& --c ri:x:z-:s, an6 Sa7=ellayLa nilgaris. "ese orgal5 slLs are aU pollv.tion tolerant, have wide geogrzphic dis%ributio?s, and are not usually dorL~antin other coituunAties in Chesapezke Pay or in other
est~~rineacd coastal areas.
5. Samples taken from the sax station were homogeneous (69.3% in
CGT-~:~)kut there x:es heterogeceiL:; 'cetweer. stat: rrs (3:. 5: in common).
!Cost spe~ieshad a rendon: distrS'c~:iori t~ithir:sraicns azd a co~tagiocs
,J; ,Y,:,,,L,,_~c9C-.: F..': 2,nl~l-g stiiziors, in~cc~i,:;~Z;l;a",rz_sr s~esieswere found in agregstes larger than the stztiozs. 76
6, The ratio of polluti~n~o~e~-a~i~ or~ti:rist!LS "; int0Perant Ones rras 7.05 Nay had the highest ratio (13 .jl) folloure9 by January (4.89) and A'i:gus t (2.46).
7. The Dean 11' diversity for tke Elizai-eth Rirer was 2*96 bits/individual. May had the lowest man diversity (2,45) followed by
January (3.23) and Awt(3.24). Because of the ray pollution tolerant species encounteyed in this st~dy,diversiLy ~msas high as
in scxe unpolluted telqerate areas.
8, Non-selective deposit feeders were reduced because of the lack of O2 and bdgh concentrations of -+S fo's-d in bottom deposits below1 cm, Suspension feeders and selective deposit feeders were
favored because of the goo3 supply of ~ie11aerated detritus in
suspension and deposited on the substrate.
,,,c spr :i ec s 9, Ht a4~~ersity-V las ~credep::2ezt o:: ricilii~s coc~onentthan on the equitcbility ccrcpone~:%. DISTRIBIITIOTS AfJD STRUCTURE OF BEIECHIC C012.:IL'iITIES IN THE HAl~iPFOX ROADS AEA, VIlGIiJIA
A Technical Ecological Report toothe Hamgton Roads Sanitation District Co;r;~lssian
Donald F. Boesch
Special Report in Applf ed 1-larine Szionce and Ocean Engfneesing Number 15
Virginia Institute cf IlsrLne Science
Glowester Polnt, :7i~zinia23362
April 1571 criterion d 225 r3-t ~2.eillto ~ecsuaatdiserepnzi Q: in s~rrrpling procedures artd disr~gardsnatural variations in rl ecies diversities. U_~pnrt,-n-.bc?conz~mitiss unil?rgoing ir.terr.al in;taSjf lit>?,such as ti12 p3pE-3T2a*1 '*.CX~%GS~.~~S"sf Iltalinia ey-id F: ,-rl~sarLzntioncd earlif?, an5 t?;oze I2 ~natrnr;L.ly rigoro'ils enviro:-.r.=ntsv:l-,ic22 exl~iisltlci;.~ divcr~iliy rrtust kc "cakcn into considea-ztioz, The=
KIT~~I-(SLO ~~5ctdtr;lk:for final subjective apprarlsa2. ef objectively derivcc? 1x1e r sr;rtai-ion.
1. T!-E mcrobsnthos of the M~~~ptor,Roads area WES surveyed
in an attcr.-$z to 2n-q7p7-&.-, -e tl-.c struztuate sf thts Irpo-&~r,? csrirj?onent sf a rxlti-zse estuzrine ecosysten. Sixteen statfms wye estab- Pished tr^t Fsz.pton Rosds, the Pmer Jcs?s River, ai-d the Elizabeth
9-".---- -,.Lv~L a;?d L"---czrrLce replicate gr:b sat-sles \:ere :&ken at. ~achstation in Febrt~~ry$ f-!ay an3 .?ugus"i7 1P59. Sediment sarples were esXccted st- eacli stat5on and &:?3lyzcd fop parziz9~sTze d5strikration.
2. O:-*e h~ndrc5sevz-.q?-five ~~c~ofaxnal tcxa :SPR~recogn ?zed
e " En t1.e LZ-->-.,- "r-c, - 16.4 :C ;.:k!:;.2 ::1"1~2 52;--?Sf ic3 t3 the, spzies level,
C'.- :.:- kzsEs of C30:.2*:3:.~ 5,. A5"~:,tke s+-atio?s were . *, - -9~v-::, f:'f~s: ,-.:%-c :?:---. - -o"i r? :-:?s ::::r - 2:-- :>-~zs;az-i?d to diificrk?$:~,cez a - eharactcri,:cd l-37 the pr.sence of- C~;:as! .; -LT s I-o-:-;rp r., T.- ;2lisza verri3.l i are-: -cj-i FT~: ,~h-iilt? ar,2 s fey lcss a5~r1'3~rit"saild- s pecif ie" spccics . "Elizabeth River stat ial-is1\ie 1-2cl~~racterized by the prrs 4. A rank analysis yield~dbislogical index vaLzs for each species within each station gro-~2. Ti-in, chree top-rank2 2~;r.il-rani-s and Spis2h2ncs fo-s ~udstati ms, Fsz-2~~ic~ito~- - 6. The structure of the co~~~anitieswas investigated by rneasvririg spccies diversity by Shar~non's fsrrula (:It ) err_? its comp:~ci-its, species ricl-mcss and ecy~i"i-abilizy. H' v:as rri3.cl1 grcatcpr amaq the sand ststions tl-tan anon3 the n;ad st:ti~.;s arid g-re~t-ex- among the E:J~ statioas tl~ancrn3ng Elizabeth Kivea -qi----- aiLo:-is. TFLe di"' L~~TSKCESin species diversity G;r;mg the "i:,rzc station groups was prizzrily attributable t o differoirces In ,he species riclmess cornpon2nt, as differences in the equitability comgsnent were slight. I However, both rickress and equitability co;r,3onents can account for sezco!:sl lif-i"cr.r.nzes in 13' within sL-;btion gro;lgb. 7'. As an index of species diveilsity, H' was s'rro;*~;lr~to be independent of sample size and sensitive to both spcies richness and equitability coxponents. 8. Ht values were ron2areri v~itl~th3se Far r~-roh,cnthos fro3 cil-ier lozations in the Vi-rcriyia area and fro3 ~tl-ier1ocatio:ls as szr??-ted in tllc iite-r2t~re, T1-2 vahes f-OF Bzytzn Rxds, espczial1;i 2bse for tl:c ~,:;r~dstclti~:;.~, were qxite high, excszdec? only by t?-.ozp. fro:? t?,e o3tscF ccn~-S;.,c.l:t~ls?leli- ar,d slop and PaciCF- c32st&lr,o;ters. II' v37Ufs POT ~il~ilypoll7ij-=id ayeas in t]~.? 3j r ~:~k~t~jEi\'.c :: I wish to ackZ.cwlcdgc the fifics.n,ial sup~o~tcf tli~ 3arr.~te;-! RO~SSznitation District Com~.issicnd;icl-i spmsorrd the study. Assistance from the Federal Water t$~s-lityLdninistrzt ion in the form of a predoetoral fellalship provided suppa& dxring the preparation of the paper. D~c.IIz~vi~iil L. ~'!ZSS !.::arriz L. Crcl;~.srdirzcced the study aided in Pogistics, and gave frsely of inforr.3tion ar3 advice. Michael D. Richards ~a provided in2 5s;ensable field assistance. My thoa~htsregardir? species diversity have benefited from discussions with rcy zsllezgues , espszially Jams K, Lcmry and Michael L. Fine. - Appendix D. Data from Water Quality Surveys and Dye Studies Figure D-1. Temperature Figure D-2. Dissolved Oxygen Figure D-3. Salinity Figure D-4. Dye for a) LWS, August 27, 1974 b) HWS, August 27, 1974 c) LlgS, August 28, 1974 d) HWS, August 28, 1974 Figure D-5. Biochemical Oxygen Demand, for HWS, August 28, 1974. Figure D-6. Dye, Lambert Point Study a) Ebb, September 20, 1973 b) Flood, September 21, 1973 WWW st!!-!'i3Zc.l WWW Pza Fd+-4H WMW Ei z a 5 ?! !-! ~ppendixE. Elizabeth River Model Section 1. Description Section 2. September 1973 Conditions Section 3. Model Calibration Section 4. Model Runs Section 5. Conclusions - ELIZABETH RIVER MODEL 1. Description VIMS' currently available (May 1975) mathematical model of the Elizabeth River is a one-dimensional, branched, tidal average, water quality model. The Elizabeth and the Southern Branch are considered to be the main stem of the river, with the Lafayette River, Eastern and Western Branches included as tributaries. The main stem has 17 segments or reaches and each tributary has three reaches. The most up- river transect is near Great Bridge and the most downriver transect is at the northern edge of Craney Island. The model can predict concentrations of conservative substances (salinity and dye have been verified to date), non-conservative substances with linear decay rates, and the coupled Dissolved Oxygen/BiochemicaP Oxygen Demand system. A more complete report will be issued shortly. Mass balance equations for each constituent are written in their complete three-dimensional form. These equations are first averaged over a cross-section and then over a complete tidal cycle. The resulting equations are then written in finite difference form and applied to the given geometry. Tidal currents, dispersion coefficients and temperature levels are inputs to the model. The DO/BOD regime includes point sources, runoff, background levels, benthal oxygen demand, photosynthesis and respiration, and natural reaeration. The BOD is separated into carbonaceous and nitrogenous fractions and each fraction has a temperature dependent decay rate, which must be specified as a part of the model input. Once the model has been applied to the geometry of the river, a calibration process is used to adjust the dispersion coefficients in order to achieve the proper distribution of a conservative substance. After calibration is complete, the model can be verified with another conservative substance, since data for both salinity and dye are available. If good data were available to quantify all the sources of BOD with reasonable accuracy, then the DO/BOD regime would provide a second means of verification. However, runoff, background levels and other factors are poorly known at present, so that the intensive survey data for DO and BOD are used to estimate these factors and slack water data are used for verification. Input parameters which will normally remain constant for the river are: tidal currents geometrical information (surface area, depths, cross-sectional areas) Input parameters which must be varied for each particular run are: temperature point sources & runoff freshwater discharge & dispersion coefficients biological factors (benthal OD, photosynthesis & respiration, k-rates, background levels) initial water quality conditions boundary conditions (4 upriver boundaries and Hampton Roads) Model output will include the concentration of all water quality constituents for each segment on each day desired during the period under investigation. In general, economic factors provide the primary limitation on the length of the period being modeled. 2. Examples of Program Inputs and Outputs In order to illustrate the type of data which are required and the format in which they are submitted, the printout from an arbitrarily chosen model run will be pre- sented. The exact conditions for which the data are the numerical representation are described in the text preceding each table. As mentioned previously, some data remain constant for most runs while others must be changed nearly every run. The data presented will be applicable only to those conditions described in the text. During the September 1973 intensive survey water temperatures were rather high (daily averages ranging from 24 to 29 degrees Centigrade), dissolved oxygen levels were in violation of water quality standards, the central portion of the river was essentially homogeneous and flushing appeared to be very weak. Subsequent surveys and data analysis have indicated that these conditions represent the "worst case conditions" which can be expected to occur during a typical year. Since the September 1973 conditions were critical ones and since field data other than those collected by VIMS are not available in the literature, most model runs were made using the September 1973 conditions. Geometric Data Cross-sectional area and distance from Sewell's Point for each transect are given in Table 1. Also given in the same table are the volume and surface area for each reach or segment. These values will remain constant, unless a new segmentation is used or until dredging or other eng- ineering projects modify the bottom topography, Current Speeds The freshwater discharge and the tidal velocity for each transect are given in Table 2A. The freshwater discharge determines the advective flow and the tidal velocities are used to calculate dispersion coefficients, The weighting factors are used in the numerical methods which transform the differential equations to finite difference form. The freshwater discharges listed in Table 2 are for September 1973. The tidal currents were calculated from tidal prisms and will be constant for most conditions. The calculated dispersion coefficients for September 1973 flow conditions are listed in Table 2B. The dispersion coefficient is assumed to be a function of the tidal velocity, the cross-sectional area and a factor, a5pha. An alpha must be chosen for each segment and for each set of flow conditions. For example during some parts of the year there is strong vertical salinity stratification in Hampton Roads and the Table 2A. Freshwater Discharge, Tidal Velocity and Weighting Factors. Dl SCf-dARGE WEIGHTING FACTOR TIDAL VELOCl TY CFS FEET/SECOND EL I ZABEBH RIVER-SOUTHERN BftANCH tAS1ERN BRANCH LAFAYETTE RIVER Table 2B. Dispersion Coefficients ******DHSPERSIOM COEFFICIENT, SQUARE FEET / SECOND****** ELIZABETH RIVER-SOUTHERN BRANCH 112 Elizabeth. This sets up a non-tidal circulation which increases flushing. During September 1973, the Elizabeth was nearly homogeneous and non-tidal circulation can be assumed to have been very small. Each set of flow con- ditions will have its own set of values for alpha, which must be selected by trial and error during the calibration process. Biological Parameters In Table 3 water temperatures for September 1973, photosynthesis and respiration and benthic oxygen demand are listed. As stated previously, the latter terms are set equal to zero due to lack of data. Initial Conditions Initial conditions for dye, salinity, C-BOD, N-BOD and DO for September 1973 are listed in Table 4. It should be noted that the initial conditions will not affect the equilibrium conditions. Only the time required to go from the initial conditions to equilibrium levels will be affected by the choice of initial values. Sources Sources of dye, DO and BOD for each reach are listed in Table 5. The BOD sources are divided into carbon- aceous and nitrogenous fractions and also into point sources and runoff. For all runs made to date, runoff inputs and DO sources have been held at zero levels. The BOD point sources listed are those for all known industrial and Table 3. Biological Parameters. TEMPERATUWt PHOTOSYNTi-iESIS AND RESPIKATIBN BENTHIC DEMAND DEGREE-C CFS * PPM CFS * PVM ELIZAStTH RIVER-SOUTHERN BKANCH EASTERN BRANCH WkSIEKN BKANCH LAFAYtTTE KIVER - H ri-F. p- e, P GCO €4 1 e LJlVlvl 080 000 600 Table 5. Sources OYE SOURCE C-POD SOURCE C-OOD SOURCE FROM SEWAGE OUTFALL FROM RUNOFF PPD * CFS PPFS * CFS PPM J( CFS ELIZABETH RIVER-SOUTHERN BRANCH EASTERN URAMCH HtSTEKN BRANCH LAFAYETTE RIVER 116 Table 5. (ContId) N-80D SOURCE N-BOD SOURCE DO SOURCE FROM SEWAGE OUTFALL FROM RUNOFF PPM * CFS PPM * CCFS PPM * CFS municipal sources along the Elizabeth with the BOD5 concen- tration reduced to LO mg/R. Since relatively little information is available on the carbonaceous and nitrogenous fractions of the wastes entering the Elizabeth River, it was necessary to make certain assumptions. These were: 1) Ultimate C-BOD = 1.5 BOD5 2) Ultimate N-BOD = 4.57 TKN concentration. 3) For primary treatment: N-BOD = C-BOD/1.21 4) For secondary treatment: N-BOD = C-BOD/0,55 or C-BOD = 45 mg/R = 1.5 (30 mg/R of BOD5) NBOD = 82 mg/R = 4.57 (18 mg/R of TKN) The decay rates used were 0.15 per day for the carbonaceous fraction and 0.10 per day for the nitrogenous fraction at 20 degrees Centigrade. The reaeration rates were calculated from the formula: where U is the velocity, H is the depth. The formula for correction to other temperatures is: -Background Concentrations Background concentrations of C-BOD and N-BOD are listed in Table 6. During September 1973 salinity ranged 118 Table 6. Background Concentrations C-BOD BACKGKOUND N-BUD BACKGROUND ELIZABETH RIVER-SOUTHERN BRANCH EASTERN BRANCW WESTEhN BRANCH 119 from 21 parts per thousand in Hampton Roads to 17 ppt at Great Bridge. It is therefore reasonable to assume that most of the water in the system was derived from Hampton Roads. BOD, like salt, will be transported from Hampton Roads into the Elizabeth, but unlike salt, it will be reduced by decay as well as dispersion. The data shown in Table 6 are the background concentrations for September 1973 flow condition if all point sources were eliminated and if the levels in Hampton Roads were held at 0.5 mg/R of C-BOD and 2.0 mg/R N-BOD. These boundary values were selected after examination of slack water monitoring data for the Hampton Roads system in the summer of 1974. Boundary Conditions Dye, salinity, BOD and DO levels at the four up- stream boundaries and in Hampton Roads are listed in Table 7. These values are for the September 1973 flow conditions and all point sources with a 10 mg/R BOD5 concentration. The DO levels were 90% saturation for the given temperature and salinity. 3. Model Calibration The data from the intensive survey on September 20 and 21, 1973 were used to calibrate and verify the water quality model of the Elizabeth. Both field data and model predictions are shown in Figures 1 to 6 for salinity, dye and dissolved oxygen in the main stem and the tributaries of the river. In general, the agreement is very good, for AVERAGE OVER SEPT. 20 -% 21 FIELD DATA 0 I MODEL - - - - DISTANCE FROM MOUTH (lo4FT.1 REACH NO. Figure 1. DYE CONCENTRATION (PPB) the conservative substances dye and salinity, but not quite so good for DO. One can note that there was a significant variation in daily averages for several stations, so that the discrepancies can be attributed to natural variations as well as the limitations of the model. 4. Model Runs Two sets of model runs were made. For the first set, the municipal and industrial discharges listed in Table 8 were used as sources of BOD, Four runs were made: all discharges, all but the Lambert Point STP, all but the Army Base STP, all discharges but the Lambert Point and Army Base STP's. For these runs the DO levels initially and at all boundaries were 6 mg/Q; C-BOD and N-BOD levels were 0.5 mg/R at the Hampton Roads boundary and up to segment 5 for back- ground levels and 1.5 mg/Q at the Great Bridge boundary and down to segment 4 for background levels. September 1973 flow conditions and water temperatures were used. For all cases, DO averages of less than 5 mg/Q were predicted. Since there is considerable latitude in the choice of boundary conditions and the background levels of BOD, one method to bypass this problem is to determine the change in DO levels which can be attributed to each source. The data listed in Table 9 are the changes in DO concentra- tions due to the Army Base and Lambert Point discharges at . . fi 4 dm; *NO 6 ; : 4 O Odr- Nm or-e'm * *\Dm 4 d m al Pr) ,-i ' 0 om0 000 0 0 0 0 m mom o~mn 4 4 n n 9 - - C hhh €ohm h h h - rn mr-N om0 N 0' m Cn 9 -dm or-o a m m ,-i Fr ... .,,,,,, .,,,,,, 4dNI 040 9,s4 3 -U9 0 mmhl m 4 om0 cu h* Ti+ N+* 0-0 * m 4 r-4 C 0 0 eee 2 6 m-4 0-0 G 6 4 CS r-mm 4-4 129 Table 9, DO variations Lambert Point Army Base DO DO Reach Difference Difference (mg/R (mg/R 1 Southern Branch 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 96 17 18 Eastern Branch a 2 3 Western Branch 1 2 3 Laf ayette River 1 the following loading rates: Lambert Point Army Base Discharge (MGD) 35 18 BOD5 Concentration 30 (mg/ R One can note that the effects of the Lambert Point plant are roughly four times as great as those due to the Army Base plant. This is due to the greater flow rate and the more upriver discharge point of Lambert Point. Hawever, for both cases the effects are felt far upstream and the point of maximum impact also is several miles upriver. This is just one more indication of the fact that tidal mixing disperses materials throughout the Elizabeth River system and that during periods typified by a homogeneous water mass, flushing is small. As mentioned previously, there is considerable latitude in the choice of boundary conditions. Furthermore, the choice of the appropriate background levels is not apparent either. First the data from slack water runs in Hampton Roads were examined to determine the likely concen- trations there. Although there was considerable variation during the summer of 1974, it appears that C-BOD levels are low and that a value of 0.5 mg/R is reasonable. The Total Kjeldahl Nitrogen levels were on the order of 0.4 to 0.6 mg/R, which gives a N-BOD level of roughly 2.0 mg/R if one assumes that a stochiometric relationship holds between TRN and nitrate-nitrogen. Therefore the downstream boundary conditions were chosen to be 0.5 mg/Q of C-BOD and 2.0 mg/Q of N-BOD. Next a series of runs was made to determine the upstream boundary conditions and the background levels. During September 1973 the salinity values at Sewell's Point and at Great Bridge were 21 ppt and 17 ppt respectively. These data, plus rainfall measurements from the Norfolk Air- port, indicated that the freshwater runoff during the month was very slight and that most of the water in the Elizabeth River system was derived from Hampton Roads. Therefore it could be assumed that Hampton Roads would be the dominant source of background BOD as well, If BOD were a conservative substance, then one could simply multiply the salinity values by an appropriate constant. However, BOD is not conservative so that it was necessary to make several model runs to select the proper upstream boundary conditions, All point sources of C-BOD and N-BOD were assumed to be zero, and high values were selected for the upstream boundary conditions. These values were then reduced on each subsequent run until the equilibrium concentrations decreased monotonically from Hampton Roads to Great Bridge. The upstream boundary con- ditions which meet this criterion were assumed to be the proper ones. The resulting concentration distributions of C-BOD and N-BOD were assumed to be the background concentra- tions which would result when Hampton Roads is the source of the substances. These concentrations are listed in Table 6. Once these values had been determined, it was possible 132 to make runs with point sources of BOD as well, The final set of runs was made as an academic exercise to see just what level of treatment would be required before DO violations were eliminated. DO levels at the boundaries were held at 90% saturation for the given salinity and temperature. The effluent streams are listed in Table 8. Three runs were made, with the effluent streams subject to increasing levels of treatment: a) all effluents with 30 mg/R or less of BODg b) all effluents with 20 mg/R or less of BOD5. C) all effluents with 10 mg/R or less of BOD5. The equilibrium DO concentrations for each of these runs are listed in Table 10. There were DO standard violations for the first two runs, but with all discharges at a concentration of 10 mg/R no violations occurred. The minimum value for this run was 5.23 mg/R. I-- (. (. 9 LLJ