Bathymetric and Sedimentation Surveys of Mission Lake, Brown County, Kansas

Kansas Biological Survey

Applied Science and Technology for Reservoir Assessment (ASTRA)

December 2007

SUMMARY During 2007, the Kansas Biological Survey (KBS) performed bathymetric and sedimentation surveys of Mission Lake in Brown County, Kansas. Bathymetric surveys were carried out on April 4 and May 25, 2007, using acoustic echosounding apparatus linked to a global positioning system. Results indicate that in 2007 the lake had a surface area of 123 acres, a volume of 1035 acre-feet, and a maximum depth of 13.8 feet. The bathymetric survey was georeferenced to both horizontal and vertical reference datums, allowing the 2007 lake depth data to be compared to a 1923 pre-impoundment topographic map for a map-based estimate of sediment thickness. Thirteen sediment cores were extracted on June 25, 2007 for direct determination of sediment thickness. Direct measurements of sediment thickness by the coring method suggest the map-derived estimates of sediment thickness are overestimated by approximately 30%. Three sediment samples were taken from the lake on July 5, 2007, and analyzed for particle size distributions, and indicate that the majority of the accumulated sediment is in the clay particle size category.

ii

TABLE OF CONTENTS SUMMARY.....................................................................................................................i TABLE OF CONTENTS................................................................................................ii LIST OF FIGURES....................................................................................................... iii LIST OF TABLES ........................................................................................................iv LAKE HISTORY AND PERTINENT INFORMATION .................................................. 1 BATHYMETRIC SURVEYING PROCEDURES ........................................................... 4

Equipment: ........................................................................................................ 4 Pre-survey preparation:..................................................................................... 5 Survey procedures: ........................................................................................... 5 Post-processing (Visual Bottom Typer)............................................................. 8 Post-processing (ArcGIS): ............................................................................... 8

SEDIMENT SAMPLING PROCEDURES................................................................... 13 SEDIMENT SAMPLING RESULTS ........................................................................... 16 PRE-IMPOUNDMENT MAP....................................................................................... 17 COMPARISION OF MAP-DERIVED SEDIMENT THICKNESSES VERSUS SEDIMENT CORING THICKNESSES ....................................................... 22 BATHYMETRIC SURVEY RESULTS........................................................................ 24 Area-Volume-Elevation Tables........................................................................ 24

iii

LIST OF FIGURES

Figure 1. Location of Mission Lake northeast of the City of Horton, Brown

County, Kansas................................................................................... 2 Figure 2. Mission Lake Aerial Photography, 1959 and 2003. The red line

on the 1959 photo represents the current lake perimeter.................... 3 Figure 3. Acoustic and manual depth points for the April 4, 2007

bathymetric survey. ............................................................................. 6 Figure 4. Acoustic and manual depth points for the May 25, 2007

bathymetric survey. ............................................................................. 7 Figure 5. Lake depth map of Mission Lake based on April 4, 2007

bathymetric survey. ........................................................................... 10 Figure 6. Lake depth map of John Redmond Reservoir based on May 25,

2007 bathymetric survey. .................................................................. 11 Figure 7. Differences between April 4 and May 25, 2007 bathymetric

surveys.............................................................................................. 12 Figure 9. Location of KBS core samples within Mission Lake, June 27,

2007. . .............................................................................................. 14 Figure 10. Location of Black&Veatch core samples within Mission Lake,

July 5, 2007....................................................................................... 15 Figure 12. Original 1923 topographic map, scanned from Black and Veatch

report................................................................................................. 18 Figure 13. Digital elevation model created from the 1923 topographic map.

Color conventions for the lake depth legend follow those of Figures 5 and 6 for the first 14 feet of depth; contrasting colors are used for depths 14.01 - 28 to emphasize differences between lake maps......................................................... 19

Figure 14. Putative elevation difference map between 2007 bathymetric survey and 1923 Black & Veatch topographic map. Negative numbers indicate loss of material during the 84-year period; positive numbers indicate accumulated material (“siltation”) (see text for additional discussion)..................... 20

Figure 15. Comparison of sediment thicknesses derived from vibracoring versus thickness computed by differencing the 1923-2007 maps. ................................................................................................ 23

Figure 16. Graph of cumulative area by elevation. .................................................... 26 Figure 17. Graph of cumulative volume by elevation................................................. 26

iv

LIST OF TABLES

Table 1. Mission Lake sediment particle size analysis............................................16

Table 2. Coincident elevation values used for vertical adjustment of 1923 DEM....21

Table 3 Comparison of sediment thickness derived from cores versus thickness derived from 1923-2007 map differencing ................................................22

Table 4 Cumulative area in acres by tenth foot elevation increments....................24

Table 5 Cumulative volume in acres by tenth foot elevation increments ...............25

1

LAKE HISTORY AND PERTINENT INFORMATION

Mission Lake was constructed in 1924 northeast of the City of Horton, Kansas, by damming Mission Creek, a tributary to the Delaware River (Figure 1). A 1923 report by Black & Veatch Engineers evaluated five possible locations for a reservoir to serve the water supply needs of the City of Horton and recommended the present Mission Creek site (“Report on Water Supply Investigation, Horton, Kansas” prepared by Black & Veatch Consulting Engineers, 1923). The impoundment was constructed as a rolled-earth-fill dam, with subsequent post-construction improvements made to the dam and spillway. Original surface area and volume of the lake is typically cited as 169 acres and 1866 acre-feet volume. Considerable siltation has occurred within the lake, reducing the area and volume. This siltation is particularly evident in the north end of the lake (Figure 2). Various estimates of present-day area and volume have been made by different entities:

Area (acres)

Volume (acre-feet) Citation

71 493 Potential Water Quality Enhancement Strategies, Mission Lake, Horton, Kansas. BG Consultants, Lawrence, Kansas, July 2004; also, Kansas Department of Health and Environment, Total Maximum Daily Load (TMDL) for Mission Lake [area only] (http://www.kdheks.gov/tmdl/krtmdl.htm)

154 1070 National Inventory of Dams, US Army Corps of Engineers, no date

(no data) 940 Juracek, K.E., 2004, Sedimentation and occurrence and trends of selected chemical constituents in bottom sediment of 10 small reservoirs, eastern Kansas, U.S. Geological Survey Scientific Investigations Report 2004-5228. 80 p.

(no data) 849 Preliminary Renovation Plan, Mission Lake Dredging Project. Black & Veatch Corporation, September 2007. Sec. 3.1, p. 3.1.

Originally constructed as a water supply source for the town of Horton, the lake also provides recreational benefits to the city in the form of boating, fishing, swimming, and picnicking. At present, the lake does not serve as the water supply for Horton, but is planned to resume that role following lake renovation measures starting in 2008.

2

Figure 1. Location of Mission Lake northeast of the City of Horton, Brown County, Kansas.

3

Figure 2. Mission Lake Aerial Photography, 1959 and 2003. The red line on the 1959 photo represents the current lake perimeter.

4

BATHYMETRIC SURVEYING PROCEDURES The Kansas Biological Survey conducted two bathymetric surveys of Mission Lake on April 4, 2007, and May 25, 2007. The second bathymetric survey was requested by the Kansas Water Office, following heavy rainfall in the Mission Creek watershed during May 2007. The May 25 survey was intended to determine if any significant sediment accumulation had occurred as a result of the heavy inflow to the lake. Both surveys were functionally identical in terms of equipment, survey procedures, and post-processing of the bathymetric data, and thus the following technical discussion encompasses both surveys. Any differences in methods or processing between the two dates of data are noted in the appropriate sections. Equipment: KBS runs a Biosonics DT-X acoustic echosounding system (www.biosonicsinc.com) with a 200 kHz split-beam transducer and a 38-kHz single-beam transducer. Latitude-longitude information is provided by a JRC global positioning system (GPS) that interfaces with the Biosonics system. ESRI’s ArcGIS is used for on-lake navigation and positioning, with GPS data feeds provided by the Biosonics unit through a serial cable. Power is provided to the echosounding unit, command/navigation computer, and auxiliary monitor by means of a Yamaha generator. Pre-survey preparation: Prior to conducting a lake bathymetric survey, geospatial data of the target lake is acquired, including georeferenced National Agricultural Imagery Project (NAIP) photography. The lake boundary was digitized as a polygon shapefile from the 2005 FSA NAIP georeferenced aerial photography obtained online from the Data Access and Service Center (DASC) at the Kansas Geological Survey. Immediately before the lake survey on each date, the elevation of the lake surface is established. The City of Horton placed, at KBS’s request, a surveyed benchmark of known elevation (1052.01 feet / 320.65 meters above sea level) at the west end of the dam. This benchmark (brass disk set in concrete) was used as the reference on survey dates. A laser line was established (using a David White Auto Laser Level with detector) from this surveyed benchmark to the water surface at the edge of the lake. Date Elevations (feet) Elevations (meters)

April 4, 2007 1049.06 319.75

May 25, 2007 1049.60 319.92 Calibration (Temperature and ball check): After boat launch and initialization of the Biosonics system and command computer, system parameters are set in the Biosonics Visual Acquisition software. The temperature of the lake at 1-2 meters was taken with a research-grade Clinefinder metric electronic thermometer. This temperature, in degrees Celsius, is input to the Biosonics Visual Acquisition software to calculate the speed of sound in water at the given temperature at the given depth. Start range, end range,

5

ping duration, and ping interval are also set at this time. A ball check is performed using a tungsten-carbide sphere supplied by Biosonics for this purpose with each transducer. The ball is lowered to a known distance below the transducer face. The position of the ball in the water column (distance from the transducer face to the ball) is clearly visible on the echogram. The echogram distance is compared to the known distance to assure that parameters are properly set and the system is operating correctly. Survey procedures: KBS followed our standard small-lake bathymetric survey practice of tracing the perimeter of the lake, maneuvering as close to shore as permitted by boat draft, transducer depth, and shoreline obstructions, in order to establish near-shore lake bottom drop-off. Following shoreline tracing, preset transect patterns were then followed. Transect lines spaced 20 meters apart were followed. Using the GPS Extension of ArcGIS, the GPS data feed from the GPS receiver via the Biosonics echosounder, and the pre-planned transect pattern, the location of the boat on the lake in real-time is shown on the command/navigation computer screen. To assist the boat operator in navigation, an auxiliary LCD monitor is connected to the computer and placed within the easy view of the boat operator. Transducer face depth on all dates was 0.5 meters below the water surface. Data are automatically logged in new files every half-hour (approximately 9000-ping files) by the Biosonics system. Spot measurements of depth: In shallow water where the depth is within the near-field of the transducers and thus cannot be measured acoustically, spot measurements of depth are taken manually. In practice, a point shapefile is created within ArcGIS, referenced to the same datum and coordinate system as the GPS data and DT4 files (latitude-longitude, WGS84). An attribute column is added to the point file for depth measurements to be entered manually. The transducers are raised to be clear of the water, and the GPS antenna is removed from the transducer mount mast and mounted on a graduated pole that has a “foot” or disk attached to the base. To ensure a proper dispersion of spot locations across the shallow zone, the boat operator maneuvers the boat in the shallow, using the GPS position display as an aid. At regular distance intervals, the echosounder operator marks the location into the point shapefile while the person in the front of the boat takes a depth reading (in meters) and calls it out to the echosounder operator, who then manually enters the value into the attribute table. Both survey dates required large numbers of spot measurements of depth in shallow areas in order to ensure the lake bottom topography was accurately represented. Post-processing of the April 4 data suggested that spot measurements in the northernmost part of the lake did not extend far enough south into the main basin, and may not be correctly representing the bottom topography in that area (Figure 3). Thus, on the May 25 re-survey, additional points were taken such that the area of spot measurements overlapped acoustic depth measurements, ideally producing a better representation of bottom contours (Figure 4). As such, the Kansas Biological Survey recommends use of the May 25 bathymetric data set over the April 4 bathymetric data set.

6

Figure 3. Acoustic and manual depth points for the April 4, 2007 bathymetric survey.

7

Figure 4. Acoustic and manual depth points for the May 25, 2007 bathymetric survey.

8

Post-processing (Visual Bottom Typer) The Biosonics DT-X system produces data files in a proprietary DT4 file format containing acoustic and GPS data. To extract the bottom position from the acoustic data, each DT4 file is processed through the Biosonics Visual Bottom Typer (VBT) software. The processing algorithm is described as follows:

“The BioSonics, Inc. bottom tracker is an “end_up" algorithm, in that it begins searching for the bottom echo portion of a ping from the last sample toward the first sample. The bottom tracker tracks the bottom echo by isolating the region(s) where the data exceeds a peak threshold for N consecutive samples, then drops below a surface threshold for M samples. Once a bottom echo has been identified , a bottom sampling window is used to find the next echo. The bottom echo is first isolated by user_defined threshold values that indicate (1) the lowest energy to include in the bottom echo (bottom detection threshold) and (2) the lowest energy to start looking for a bottom peak (peak threshold). The bottom detection threshold allows the user to filter out noise caused by a low data acquisition threshold. The peak threshold prevents the algorithm from identifying the small energy echoes (due to fish, sediment or plant life) as a bottom echo.” (Biosonics Visual Bottom Typer User’s Manual, Version 1.10, p. 70).

Data is output as a comma-delimited (*.csv) text file. A set number of qualifying pings are averaged to produce a single report (for example, the output for ping 31 {when pings per report is 20} is the average of all values for pings 12-31). Post-processing (ArcGIS): Ingest to ArcGIS is accomplished by using the Tools – Add XY Data option. The projection information is specified at this time (WGS84). Files are displayed as Event files, and can be exported as shapefiles if desired. Typically, Event files are merged using the ArcGIS command Data Management Tools – General – Merge, and the output from this is a shapefile. Initial QA/QC is performed next. The point shapefile(s) is visually evaluated for any points with spurious lat/lon coordinates, which should be obvious (and unlikely). The attribute table is examined for any points reporting a value of 0 in the depth file, and these points are deleted. Any points with a value less than the start range of the data acquisition parameter (for the Mission Lake surveys, this value was 0.5 meters) is also deleted. In the attribute table, the adjustment for transducer depth is performed next. A new field – AdjDepth– is added to the attribute table of the point shapefile. The value for AdjDepth is calculated as AdjDepth = Depth + (Transducer Face Depth), where the Transducer Face Depth represents the depth of the transducer face below water level in meters (This value was also 0.5 meters).

9

To set depths relative to lake elevation, another field is added to the attribute table of the point shapefile, Depth_Elev. The value for this attribute is then computed as Depth_Elev = (Elevation of the Water Surface) - Adj_Depth.

A triangulated irregular network (TIN) was created using the master depth data point shapefile and the lake polygon shapefile with the lake surface elevation. Output projection is typically specified to be the same as the input data. Raster interpolation of the point data is also performed using the same input data and the Topo to Raster option within the 3D Extension of ArcGIS. Following creation of the TIN file and the raster file, any necessary projections or conversions from meters to feet units are performed (Figure 5, Figure 6). Differences between the April and May bathymetric survey maps were computed by subtracting the May bathymetric map from the April map (Figure 7). The improved bottom definition provided by the additional spot points on the May survey appears as changed areas on the difference map.

10

Figure 5. Lake depth map of Mission Lake based on April 4, 2007 bathymetric survey.

11

Figure 6. Lake depth map of Mission Lake based on May 25, 2007 bathymetric survey.

12

Figure 7. Differences between April 4 and May 25, 2007 bathymetric surveys.

13

SEDIMENT SAMPLING PROCEDURES KBS operates a Specialty Devices Inc. sediment vibracorer mounted on a dedicated 24’ pontoon boat (Figure 8). The vibracorer uses 3” diameter aluminum thinwall pipe in user-specified lengths (KBS has used up to 10’ sections). The vibracorer runs off 24-volt batteries, and uses an electric motor with counter-rotating weights in the vibracorer head unit to create a high-frequency vibration in the pipe, allowing the pipe to penetrate even solidly packed sediments and substrate as it is lowered into the lake using a manually operated winch system. Once the open end of the core pipe has penetrated to the substrate, the unit is turned off and the unit is raised to the surface using the winch. At the surface, the pipe containing the sediment core is disconnected from the vibracore head for further onboard processing. The sediment core can be cut into sections while in the pipe, the pipe bisected longitudinally for taking samples along the length of the core, or the sediment can be manually extruded from the pipe and measured. Core sampling on Mission Lake was conducted on June 26, 2007 and July 5, 2007. During the June sampling, cores from thirteen (13) sites were extracted for determination of accumulated sediment thickness only. The July sampling was conducted with and under the direction of a representative from Black and Veatch,Inc, for the preliminary engineering study being conducted by that company. At each site, determined using GPS, the core boat was anchored and the vibracore system used to extract a sediment core down to and including the upper several inches of pre-impoundment soil (substrate). The location of each core site was recorded using the GPS in UTM coordinates (NAD83, UTM Zone 15N) (Figure 9, Figure 10). For the June sampling, cores were extruded horizontally and the amount of sediment accumulation measured (from top of substrate to top of sediment core). For the July sampling, Black & Veatch segmented each core tube into sections, which were then capped, labeled, and sent to Midwest Laboratories, Inc., of Omaha, Nebraska for analysis. Results reported herein for sediment particle size analysis are extracted from the Preliminary Renovation Plan, Mission Lake Dredging Project. Black & Veatch Corporation, September 2007.

Figure 8. KBS vibe-core system.

14

Figure 9. Location of KBS core samples within Mission Lake, June 27, 2007. Numbers adjacent to each point are sediment thickness, in centimeters.

15

Figure 10. Location of Black&Veatch core samples within Mission Lake, July 5, 2007.

16

SEDIMENT SAMPLING RESULTS Particle size analysis for Mission Lake shows some expected trends. The clay component forms the dominant fraction of the total particle sizes, and the percentage of clay increases with distance from the major inflow (Mission Creek) at the north end of the lake to the south main basin of the lake (Table 1, Figure 11). MidWest Laboratories performed additional chemical and physical analyses on the three sediment cores for Black and Veatch, Inc.; results and data from those analyses can be found in the B&V 2007 final report (Preliminary Renovation Plan, Mission Lake Dredging Project, Project 148395. Black & Veatch Corporation, September 2007).

Table 1 Mission Lake sediment particle size analysis

Site MW Labs

Sample No. %Cobbles%Crs Gravel

%Fine Gravel

%Crs Sand

%Med. Sand

%Fine Sand

%All Sand %Silt %Clay

ML-1 1314447 0.0 0.0 0.0 0 0.1 1.3 1.4 57.4 41.2ML-2 1314449 0.0 0.0 0.0 0 0.0 0.8 0.8 42.1 57.1ML-3 1314451 0.0 0.0 0.0 0 0.0 0.2 0.2 29.1 70.7

Mission Lake 2007 Sediment Particle Size Analysis

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

ML-1 Headwater ML-2 Mid-Lake ML-3 Lower lake

Clay

Silt

Sand

Mission Lake 2007 Sediment Particle Size Analysis

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

ML-1 Headwater ML-2 Mid-Lake ML-3 Lower lake

Clay

Silt

Sand

Figure 11. Mission Lake Particle Size Analysis.

17

PRE-IMPOUNDMENT MAP

A pre-impoundment map of the Mission Lake site was obtained by scanning a 1:20,000-scale (approximately) map in the 1923 “Report on Water Supply Investigation, Horton, Kansas” prepared by Black & Veatch Consulting Engineers (Figure 12). The original report was located in the office of the City Manager, City of Horton, Kansas. The digital TIF image was then georeferenced using common control points to a UTM coordinate system such that the contour lines could be digitized and converted to a digital elevation model of the pre-impoundment surface, using primarily section corners and centerpoints as control points and identifying corresponding locations on US Geological Survey Digital Raster Graphic georeferenced topographic maps. Following georeferencing, contour lines were digitized from the image to a shapefile and attributed with the appropriate elevation value. The contour line file and the stream line file were input to the TIN tool in ArcGIS. The TIN tool uses the contour line file to establish elevations within a triangulated irregular network, while the stream line file is used as a breakline to “force” valley bottoms to their “true” locations. The TIN file was then converted to a raster file to facilitate comparison of elevations with the 2007 bathymetric data (present-day lake bottom elevations) (Figure 13). The contour interval on the 1923 map was noted as five (5) feet, but the values for the contours otherwise did not match current contour values. We believe that the elevations were referenced to some local benchmark or local reference system, but there was no information provided in the report or on the map regarding this. No information was available on the vertical or horizontal datum used. As a means of vertically referencing the 1923 digital elevation model, we compared elevation values for coincident locations on the 1923 DEM and a US Geological Survey 30-meter DEM (National Elevation Data, http://ned.usgs.gov/). This comparison provided an adjustment figure of 278 meters to be added to the 1923 DEM to “match” it to the USGS DEM and the 2007 bathymetry data (Table 2). Changes in lake bottom elevation between 1923 and 2007 were computed by digitally subtracting the 1923 digital elevation model from the 2007 digital elevation model. Negative numbers on the resulting output indicate loss of material during the 74-year period; positive numbers indicate accumulated material (siltation) (Figure 14). The difference map suggests that the greatest sedimentation has occurred in the former river channel, as might be expected.

Caution should be exercised in drawing conclusions based on comparison between two maps of different scales, dates, and production methods.

18

Figure 12. Original 1923 topographic map, scanned from Black and Veatch report.

19

Figure 13. Digital elevation model created from the 1923 topographic map. Color conventions for the lake depth legend follow those of Figures 5 and 6 for the first 14 feet of depth; contrasting colors are used for depths 14.01 - 28 to emphasize differences between lake maps.

20

Figure 14. Putative Elevation difference map between 2007 bathymetric survey and 1923 Black & Veatch topographic map. Negative numbers indicate loss of material during the 84-year period; positive numbers indicate accumulated material (“siltation”) (see text for additional discussion).

21

Table 2 Coincident elevation values used for vertical adjustment of 1923 DEM

Point USGS DEM elevation (meters)

1923 DEM elevation (meters)

Difference (meters)

1 313.0 36.1 277.02 319.7 42.8 276.83 319.5 42.3 277.24 323.2 47.3 275.95 330.1 48.0 282.26 332.8 46.3 286.57 319.8 37.9 281.98 326.6 46.7 279.99 319.5 47.1 272.410 324.6 46.1 278.5

Mean 278.8 standard deviation 3.97

22

COMPARISION OF MAP-DERIVED SEDIMENT THICKNESSES VERSUS SEDIMENT CORING THICKNESSES Sediment thicknesses at locations of sediment cores taken in June 2007 were compared to predicted sediment thicknesses derived from differencing the pre-impoundment map with the May 2007 bathymetric survey (Table 3). Results indicate a substantial difference between the two methods. Differences between the core and the difference map thicknesses are most likely attributable to both inaccuracies in the 1923 topographic map, and the related issue of referencing the 1923 data to a vertical datum. A scatterplot of the data and regression equation (Figure 15) yield an offset and multiplier that potentially could be used to adjust the vertical reference of the 1923 map, although this was not perfomed.

Table 3 Comparison of sediment thickness derived from cores

versus thickness derived from 1923-2007 map differencing KBS

Core No. UTMX UTMY Core thickness

(meters) Map thickness

(meters) 1 284386.30 4394492.27 0.96 3.77 2 284112.07 4395115.93 2.20 4.56 3 283853.52 4395821.80 0.14 1.71 4 284006.40 4395438.34 2.17 3.79 5 284186.19 4394943.47 0.90 2.25 6 284238.91 4394779.51 2.18 4.25 7 284268.73 4394606.87 2.35 4.21 8 284156.23 4394619.01 0.24 0.97 9 284099.59 4395274.18 0.75 2.35 10 284203.92 4395270.17 1.93 2.67 11 283984.28 4395292.12 2.10 5.12 12 284062.91 4395708.82 2.30 4.45 13 283913.54 4395624.31 2.10 4.27

23

y = 1.3357x + 1.3248R2 = 0.7549

0.00

1.00

2.00

3.00

4.00

5.00

6.00

0.00 1.00 2.00 3.00 4.00 5.00 6.00

Thickness from sediment cores (meters)

Thic

knes

s fr

om 1

923-

2007

map

diff

eren

ce

(met

ers)

Figure 15. Comparison of sediment thicknesses derived from vibracoring versus thickness computed by differencing the 1923-2007 maps.

24

BATHYMETRIC SURVEY RESULTS Area-Volume-Elevation Tables: Area-volume-elevation tables were computed for the impoundment for all elevations falling below the water surface on the date of the bathymetric mapping (Table 4, Table 5). By convention, units are expressed in acres, feet, and acre-feet, rather than the metric units in which the data were acquired. Charts of cumulative area as a function of elevation and cumulative volume as a function of elevation were also produced (Figures 16, 17).

Table 4

Cumulative area in acres by tenth foot elevation increments

2007 Survey Elevation (ft NGVD) 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

1035 0.27 1.15 2.94 5.81

1036 7.96 9.43 10.95 12.24 13.31 14.28 15.33 16.53 17.85 19.22

1037 20.49 21.68 22.71 23.67 24.69 25.80 26.93 27.99 29.20 30.34

1038 31.57 32.99 34.13 35.26 36.33 37.47 38.82 40.16 41.54 43.08

1039 44.42 46.03 47.32 48.42 49.57 50.57 51.54 52.47 53.41 54.64

1040 55.71 56.77 57.77 58.60 59.37 60.23 61.28 62.62 64.08 65.15

1041 66.02 66.83 67.70 68.55 69.46 70.56 71.67 72.56 73.30 73.94

1042 74.56 75.14 75.71 76.23 76.77 77.32 77.83 78.36 78.94 79.55

1043 80.13 80.73 81.38 82.04 82.68 83.32 84.14 84.94 85.88 86.88

1044 87.91 88.94 90.00 91.00 91.94 92.92 93.92 94.88 95.82 96.77

1045 97.74 98.63 99.46 100.27 101.06 101.86 102.73 103.45 104.20 105.08

1046 105.91 106.73 107.60 108.82 109.76 110.73 111.86 112.78 113.77 115.02

1047 115.75 116.38 116.94 117.92 118.48 118.95 119.30 119.58 119.88 120.16

1048 120.42 120.68 120.95 121.22 121.48 121.75 122.00 122.26 122.51 122.76

1049 122.99 123.23 123.42 123.61 123.76 123.93

25

Table 5

Cumulative volume in acre-feet by tenth foot elevation increments

2007 Survey Elevation (ft NGVD) 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

1035 0.03 0.14 0.44 1.02

1036 1.81 2.76 3.85 5.07 6.41 7.83 9.37 11.02 12.80 14.73

1037 16.77 18.94 21.21 23.58 26.05 28.63 31.32 34.12 37.04 40.08

1038 43.23 46.53 49.94 53.47 57.10 60.85 64.73 68.75 72.90 77.21

1039 81.65 86.26 90.99 95.83 100.79 105.84 111.00 116.25 121.59 127.05

1040 132.62 138.30 144.08 149.94 155.87 161.90 168.02 174.29 180.69 187.21

1041 193.81 200.50 207.27 214.12 221.07 228.12 235.29 242.55 249.88 257.27

1042 264.73 272.24 279.81 287.44 295.11 302.84 310.63 318.46 326.36 334.31

1043 342.33 350.40 358.54 366.74 375.01 383.34 391.75 400.25 408.84 417.53

1044 426.32 435.21 444.21 453.31 462.50 471.80 481.19 490.68 500.26 509.94

1045 519.71 529.57 539.52 549.55 559.65 569.84 580.11 590.46 600.88 611.38

1046 621.97 632.65 643.41 654.29 665.27 676.34 687.53 698.80 710.18 721.68

1047 733.26 744.90 756.59 768.38 780.23 792.12 804.05 816.01 828.00 840.02

1048 852.06 864.13 876.22 888.34 900.49 912.67 924.87 937.09 949.34 961.62

1049 973.92 986.24 998.58 1010.94 1023.32 1035.71

26

0

25

50

75

100

125

150

1035

.0

1036

.0

1037

.0

1038

.0

1039

.0

1040

.0

1041

.0

1042

.0

1043

.0

1044

.0

1045

.0

1046

.0

1047

.0

1048

.0

1049

.0

Elevation (feet.tenths)

Cum

ulat

ive

Are

a (a

cres

)

Figure 16. Graph of cumulative area by elevation.

0

250

500

750

1000

1250

1035

.0

1036

.0

1037

.0

1038

.0

1039

.0

1040

.0

1041

.0

1042

.0

1043

.0

1044

.0

1045

.0

1046

.0

1047

.0

1048

.0

1049

.0

Elevation (feet.tenths)

Cum

ulat

ive

Volu

me

(acr

e-fe

et)

Figure 17. Graph of cumulative volume by elevation.