RANDO-002 Final Report

DAM HYDRAULIC CAPACITY
ASSESSMENT REPORT
(DRAFT)
SCHOONBECK LAKE DAM
RANDO-002
RANDOLPH COUNTY, NC
PREPARED BY:
HDR Engineering Inc. of the
Carolinas under contract with
WOOD E&I Solutions
2020

EXECUTIVE SUMMARY
A hydraulic capacity analysis was completed for the Schoonbeck Lake Dam in Randolph County,
North Carolina. The purpose of the study was to analyze the existing potential of the dam for
overtopping during predetermined specified rainfall events using the North Carolina Dam Safety
defined process and templates. The analyses were completed using the United States Army Corps
of Engineers developed software Hydrologic Engineering Center – Hydrologic Modeling System
(HEC-HMS) in combination with Arc-GIS to develop required input parameters. The rainfall
events included in the analyses consist of 24-hour durations with return periods of 25 years, 50
years, 100 years, 200 years, 500 years and 1000 years. Results of the analyses indicate that this
structure is hydraulically adequate for 25 years, 50 years, 100 years, 200 years, 500 years, and
1000 years rainfall events. Data, input parameters, and final results can be found on the attached
summary sheets and in the appendices of this report as well as in the associated electronic file in
which all program files are stored.
Drainage Area (Sq. Mi.)=
Curve Number =
Lag Time (min.)=
Rainfall Distribution Methods =
SUMMARY SHEET OF HYDRAULIC CAPACITY RESULTS
SCHOONBECK LAKE DAM, RANDO-002
ANALYSIS PERFORMED BY: S. MURPHY, HDR
78.38
25
SCS Type 2
24 HOUR - 200 YEAR EVENT, 8.18 INCHES, ELEVATION 564.7 (2.4 FT FREE-BOARD)
24 HOUR - 100 YEAR EVENT, 7.42 INCHES, ELEVATION 564.5 (2.6 FT FREE-BOARD)
24 HOUR - 50 YEAR EVENT, 6.67 INCHES, ELEVATION 564.2 (2.9 FT FREE-BOARD)
24 HOUR - 25 YEAR EVENT, 5.95 INCHES, ELEVATION 564 (3.1 FT FREE-BOARD)
TOP OF DAM ELEVATION = 567.1
24 HOUR - 1000 YEAR EVENT, 10 INCHES, ELEVATION 565.3 (1.8 FT FREE-BOARD)
24 HOUR - 500 YEAR EVENT, 9.22 INCHES, ELEVATION 565.1 (2 FT FREE-BOARD)
SPILLWAY TYPE
Barrel
Barrel
ELEVATION
SUMMARY OF INPUT PARAMETERS
0.08
564.2
564.7
565.2
565.7
566.2
566.7
562.7
565.5
ELEVATION
562.7
563.2
563.7
STORAGE (ACRE-FT)
325.2
337.5
350.0
37.6
43.2
567.2 49.0
STORAGE (ACRE-FT)
0.0
5.2
10.5
15.8
21.2
26.6
32.1
ELEVATION
583.2
583.7
584.2
584.7
585.2
585.7
586.2
586.7
587.2
587.7
362.8
375.8
389.0
402.4
416.0
429.8
443.7
Primary
Auxiliary
RANDO-002SCHOONBECK LAKE DAM OCTOBER 5, 2020
570.2
570.7
571.2
571.7
572.2
572.7
567.7
568.2
568.7
569.2
569.7
577.2
577.7
578.2
578.7
573.2
573.7
574.2
574.7
575.2
575.7
54.8
60.9
67.1
582.2
582.7
579.2
579.7
580.2
580.7
581.2
581.7
576.2
576.7
129.0
136.7
144.6
152.7
73.4
79.9
86.5
93.3
100.1
107.1
278.5
289.8
301.3
313.1
215.5
225.4
235.6
246.0
256.6
267.4
160.9
169.4
178.2
187.1
196.3
205.8
114.2
121.6
590.2
590.7
591.2
588.2
602.2
592.2
592.7
593.2
593.7
594.2
588.7
589.2
589.7
602.7
597.7
598.2
598.7
599.2
599.7
600.2
600.7
601.2
601.7
594.7
595.2
595.7
596.2
596.7
597.2
591.7
546.3
561.6
577.0
592.5
608.2
457.9
472.2
486.7
501.3
516.2
922.2
NOT TO SCALE
819.9
836.8
853.7
870.7
887.8
905.0
720.4
736.8
753.2
769.8
786.4
803.1
623.9
639.7
655.7
671.7
687.8
704.1
531.2
RANDO-002SCHOONBECK LAKE DAM OCTOBER 5, 2020

APPENDIX A
Watershed Boundary

Sources: Esri, HERE, Garmin, USGS, Intermap, INCREMENT P,NRCan, Esri Japan, METI, Esri China (Hong Kong), Esri Korea,Esri (Thailand), NGCC, (c) OpenStreetMap contributors, and theGIS User Community
Schoonbeck Lake Dam - RANDO-002 - Watershed Boundary
Legend
Longest FlowPath
Watershed Bound ary
0 0.1 0.20.05 Miles
Date: 10 /2/2020
/Drainage Area: 0.08 Square MilesFlowpath Length: 3983.5 feet

APPENDIX B

Lag Time Calculation
Dam No:RANDO-002 Date:10/8/2020
Dam Name:Schoonbeck Lake Dam Engineer:K. Trefzger
Maximum Potential Retention (inches):S =(1000/cn')-10
Time of Concentration (hours):Tc =l0.8*(S+1)0.7
1140*Y0.5
Basin Data:Input Values in yellow
Curve Number CN =78.3752 from NRCS CN Calculation
S =2.75914 in.
Mean Basin Slope Y =5.70755 %from Watershed Mean slope
Longest Flowpath:0.75 mi.from Watershed Longest flowpath
Flow Length l =3960 ft.
Time of Concentration Tc =0.70 Hours Tc =42 mins
Lag Time TL =0.42 Hours TL =25 mins

APPENDIX C
NRCS Curve Number Summary Sheet

Change CN according to TR-55 (see tables below)
NLCD (2016) Landuse TR-55 Landuse HSG A (sq. ft.)CN HSG B (sq. ft.)CN HSG C (sq. ft.)CN HSG D (sq. ft.)CN
Open Water Not Available 0 100 0 0 100 0 883 100 88287 416887 100 41688719
Developed, Open Space Open space - Fair condition (grass cover 50% to 75%)0 49 0 0 69 0 0 79 0 59019 84 4957617
Developed, Low Intensity Residential districts by average lot size: 1/3 acre 0 57 0 0 72 0 0 81 0 38742 86 3331836
Developed, Medium Intensity Residential districts by average lot size: 1/8 acre 0 77 0 0 85 0 0 90 0 9686 92 891073
Developed, High Intensity Urban districts - Commercial and business 0 89 0 0 92 0 0 94 0 0 95 0
Barren Land Newly graded areas 0 77 0 0 86 0 0 91 0 0 94 0
Deciduous Forest Woods - Fair 0 36 0 345787 60 20747214 530057 73 38694169 90983 79 7187628
Evergreen Forest Woods - Fair 0 36 0 44 60 2653 15844 73 1156591 1283 79 101354
Mixed Forest Woods - Fair 0 36 0 20134 60 1208013 180275 73 13160071 34968 79 2762491
Shrub/Scrub Brush - Fair 0 35 0 170 56 9500 237 70 16561 17884 77 1377073
Herbaceuous Herbaceuous - Fair 0 60 0 0 71 0 0 81 0 54674 89 4865964
Hay/Pasture Pasture - Fair 0 49 0 45628 69 3148343 202588 79 16004413 89884 84 7550268
Cultivated Crops Row crops (SR + CR) - Poor 0 71 0 0 80 0 0 87 0 0 90 0
Woody Wetlands Not Available 0 80 0 0 85 0 0 90 0 0 95 0
Emergent Herbaceuous Wetlands Not Available 0 80 0 0 85 0 0 90 0 0 95 0 Weighted CN=78.38
NOTE: Curve Numbers are from SCS TR-55 with the exception of assumed HSG A (CN=60) for Herbaceous,Open Water, Woody Wetlands, and Emergent Herbaceous
Wetlands.
NOTE: double-check all the land types are being calculated and texts are accurate
NOTE: double-check the exported attribute table has the same table format as the "Export_Output" table

APPENDIX D
Hyetograph Results Used for Analysis

0.0
2.0
4.0
6.0
8.0
10.0
12.0
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24Cumulative Depth (in)Time (hrs)
Hyetographs for 24-Hour SCS Type II Rainfall Distributions
25YR
50YR
100YR
200YR
500YR
1000YR

APPENDIX E
NOAA Atlas 14 Rainfall Table

Point precipitation frequency estimates (inches)
NOAA Atlas 14 Volume 2 Version 3
Data type: Precipitation depth
Time series type: Partial duration
Project area: Ohio River Basin
Location name (ESRI Maps): Denton, North Carolina USA
Station Name: -
Latitude: 35.687372°
Longitude: -80.01919°
Elevation (USGS): 580.84 ft
PRECIPITATION FREQUENCY ESTIMATES
by
duration
for ARI
(years):1 2 5 10 25 50 100 200 500 1000
5-min:0.396 0.47 0.546 0.598 0.655 0.691 0.723 0.749 0.774 0.79
10-min:0.633 0.751 0.875 0.957 1.04 1.1 1.15 1.19 1.23 1.25
15-min:0.792 0.944 1.11 1.21 1.32 1.39 1.45 1.5 1.54 1.56
30-min:1.09 1.3 1.57 1.75 1.96 2.1 2.22 2.33 2.45 2.53
60-min:1.35 1.64 2.02 2.28 2.61 2.85 3.06 3.27 3.52 3.69
2-hr:1.59 1.93 2.39 2.73 3.16 3.48 3.79 4.09 4.47 4.75
3-hr:1.7 2.06 2.56 2.93 3.42 3.79 4.15 4.51 4.98 5.33
6-hr:2.06 2.48 3.09 3.56 4.17 4.66 5.14 5.63 6.29 6.79
12-hr:2.44 2.95 3.7 4.28 5.08 5.71 6.37 7.04 7.98 8.72
24-hr:2.88 3.48 4.35 5.03 5.95 6.67 7.42 8.18 9.22 10
2-day:3.36 4.04 5.01 5.76 6.76 7.55 8.35 9.18 10.3 11.2
3-day:3.56 4.28 5.29 6.07 7.12 7.95 8.8 9.66 10.8 11.8
4-day:3.77 4.52 5.56 6.37 7.48 8.35 9.24 10.2 11.4 12.4
7-day:4.32 5.15 6.25 7.13 8.32 9.26 10.2 11.2 12.6 13.6
10-day:4.91 5.84 7.02 7.93 9.17 10.1 11.1 12.1 13.5 14.5
20-day:6.61 7.79 9.2 10.3 11.8 13 14.2 15.5 17.1 18.4
30-day:8.16 9.59 11.1 12.3 13.9 15.1 16.4 17.6 19.2 20.4
45-day:10.3 12 13.8 15.1 16.9 18.2 19.5 20.8 22.5 23.8
60-day:12.3 14.3 16.2 17.6 19.4 20.8 22.1 23.4 25.1 26.3
Date/time (GMT): Thu Oct 8 20:43:19 2020
pyRunTime: 0.0615329742432

APPENDIX F
Outlet Works Rating Curves

Total outlet discharge from the spillway systemClient:NCEMDate:9/30/2020Project:Overtopping StudyEngineer:T. CarterDam:Schoonbeck Lake DamDam No.RANDO-002Reservior Water Level (RWS) Elevation (ft)Total discharge from the spillway system (cfs)(from Hydrocad)562.700.00563.501.50564.302.13565.102.60565.905.27566.7019.08567.5031.43568.3039.47569.1046.04569.9051.75570.7056.86571.5061.53572.3065.86573.1069.91573.9073.73574.7077.36575.5080.82576.3084.13577.1087.32577.9090.39578.7093.36579.5096.24580.3099.03581.10101.74581.90104.38582.70106.96583.50109.47584.30111.93585.10114.33585.90116.69586.70118.99587.50121.25588.30123.47589.10125.65589.90127.79590.70129.90591.50131.97592.30134.01593.10136.02593.90138.00594.70139.95595.50141.88596.30143.78597.10145.65597.90147.50598.70149.33599.50151.13600.30152.91601.10154.68601.90156.42602.70158.140.0020.0040.0060.0080.00100.00120.00140.00160.00560.00 565.00 570.00 575.00 580.00 585.00 590.00 595.00 600.00 605.00Total discharge from the spillway system (cfs)Reservior Water Level (RWS) Elevation (ft)The whole spillway system rating curve (cfs)
RANDO-002 Schoonbeck Lake Dam
Rainfall not specifiedRANDO-002
Printed 10/29/2020Prepared by HDR, Inc
Page 1HydroCAD® 10.00-25 s/n 07102 © 2019 HydroCAD Software Solutions LLC
Summary for Pond 1P: RANDO-002_Schoonbeck Lake Dam
Volume Invert Avail.Storage Storage Description
#1 562.70' 40,172,648 cf Custom Stage Data (Prismatic) Listed below (Recalc)
RANDO-002 Schoonbeck Lake Dam
Rainfall not specifiedRANDO-002
Printed 10/29/2020Prepared by HDR, Inc
Page 2HydroCAD® 10.00-25 s/n 07102 © 2019 HydroCAD Software Solutions LLC
Elevation Surf.Area Inc.Store Cum.Store
(feet) (sq-ft) (cubic-feet) (cubic-feet)
562.70 454,600 0 0
563.20 457,998 228,150 228,150
563.70 461,299 229,824 457,974
564.20 464,521 231,455 689,429
564.70 467,461 232,996 922,424
565.20 474,600 235,515 1,157,940
565.70 480,205 238,701 1,396,641
566.20 486,406 241,653 1,638,294
566.70 494,326 245,183 1,883,477
567.20 505,537 249,966 2,133,442
567.70 517,031 255,642 2,389,084
568.20 533,486 262,629 2,651,714
568.70 548,525 270,503 2,922,216
569.20 560,801 277,332 3,199,548
569.70 570,469 282,818 3,482,365
570.20 580,078 287,637 3,770,002
570.70 590,371 292,612 4,062,614
571.20 601,934 298,076 4,360,691
571.70 615,635 304,392 4,665,083
572.20 630,088 311,431 4,976,514
572.70 645,322 318,853 5,295,366
573.20 660,303 326,406 5,621,772
573.70 676,904 334,302 5,956,074
574.20 693,906 342,703 6,298,777
574.70 712,676 351,646 6,650,422
575.20 731,582 361,065 7,011,487
575.70 749,531 370,278 7,381,765
576.20 769,277 379,702 7,761,467
576.70 789,580 389,714 8,151,181
577.20 812,500 400,520 8,551,701
577.70 834,580 411,770 8,963,471
578.20 857,100 422,920 9,386,391
578.70 876,152 433,313 9,819,704
579.20 894,971 442,781 10,262,485
579.70 914,063 452,259 10,714,743
580.20 934,063 462,032 11,176,775
580.70 955,176 472,310 11,649,085
581.20 975,488 482,666 12,131,751
581.70 995,703 492,798 12,624,548
582.20 1,016,973 503,169 13,127,717
582.70 1,039,014 513,997 13,641,714
583.20 1,061,113 525,032 14,166,746
583.70 1,082,305 535,855 14,702,600
584.20 1,101,328 545,908 15,248,509
584.70 1,120,156 555,371 15,803,880
585.20 1,139,932 565,022 16,368,902
585.70 1,161,475 575,352 16,944,253
586.20 1,178,105 584,895 17,529,148
586.70 1,193,301 592,852 18,122,000
RANDO-002 Schoonbeck Lake Dam
Rainfall not specifiedRANDO-002
Printed 10/29/2020Prepared by HDR, Inc
Page 3HydroCAD® 10.00-25 s/n 07102 © 2019 HydroCAD Software Solutions LLC
587.20 1,207,900 600,300 18,722,300
587.70 1,222,705 607,651 19,329,951
588.20 1,239,004 615,427 19,945,379
588.70 1,255,205 623,552 20,568,931
589.20 1,270,303 631,377 21,200,308
589.70 1,284,844 638,787 21,839,095
590.20 1,299,229 646,018 22,485,113
590.70 1,313,447 653,169 23,138,282
591.20 1,325,762 659,802 23,798,084
591.70 1,337,480 665,811 24,463,895
592.20 1,347,402 671,221 25,135,115
592.70 1,356,914 676,079 25,811,194
593.20 1,365,957 680,718 26,491,912
593.70 1,375,068 685,256 27,177,168
594.20 1,384,492 689,890 27,867,058
594.70 1,393,115 694,402 28,561,460
595.20 1,401,855 698,743 29,260,202
595.70 1,409,707 702,891 29,963,093
596.20 1,417,246 706,738 30,669,831
596.70 1,424,580 710,457 31,380,288
597.20 1,431,758 714,085 32,094,372
597.70 1,438,486 717,561 32,811,933
598.20 1,445,273 720,940 33,532,873
598.70 1,452,510 724,446 34,257,319
599.20 1,458,818 727,832 34,985,151
599.70 1,465,264 731,021 35,716,171
600.20 1,471,836 734,275 36,450,446
600.70 1,478,184 737,505 37,187,951
601.20 1,484,824 740,752 37,928,703
601.70 1,492,148 744,243 38,672,946
602.20 1,499,717 747,966 39,420,912
602.70 1,507,227 751,736 40,172,648
Device Routing Invert Outlet Devices
#1 Primary 531.20'6.0" Round 6" DIP
L= 142.0' RCP, sq.cut end projecting, Ke= 0.500
Inlet / Outlet Invert= 531.20' / 529.80' S= 0.0099 '/' Cc= 0.900
n= 0.012, Flow Area= 0.20 sf
#2 Device 1 562.70'8.0" Horiz. Riser C= 0.600 Limited to weir flow at low heads
#3 Secondary 565.50'18.0" Round 18" RCP X 3.00
L= 24.5' RCP, sq.cut end projecting, Ke= 0.500
Inlet / Outlet Invert= 565.50' / 565.10' S= 0.0163 '/' Cc= 0.900
n= 0.013 Concrete pipe, bends & connections, Flow Area= 1.77 sf
Primary OutFlow Max=0.00 cfs @ 5.00 hrs HW=0.00' TW=525.90' (Fixed TW Elev= 525.90')
1=6" DIP ( Controls 0.00 cfs)
2=Riser ( Controls 0.00 cfs)
Secondary OutFlow Max=0.00 cfs @ 5.00 hrs HW=0.00' (Free Discharge)
3=18" RCP ( Controls 0.00 cfs)
RANDO-002 Schoonbeck Lake Dam
Rainfall not specifiedRANDO-002
Printed 10/29/2020Prepared by HDR, Inc
Page 4HydroCAD® 10.00-25 s/n 07102 © 2019 HydroCAD Software Solutions LLC
Stage-Discharge for Pond 1P: RANDO-002_Schoonbeck Lake Dam
Elevation
(feet)
Discharge
(cfs)
Primary
(cfs)
Secondary
(cfs)
562.70 0.00 0.00 0.00
563.10 1.06 1.06 0.00
563.50 1.50 1.50 0.00
563.90 1.84 1.84 0.00
564.30 2.13 2.13 0.00
564.70 2.38 2.38 0.00
565.10 2.60 2.60 0.00
565.50 2.81 2.81 0.00
565.90 5.27 2.83 2.44
566.30 11.44 2.84 8.60
566.70 19.08 2.86 16.22
567.10 26.41 2.87 23.53
567.50 31.43 2.89 28.54
567.90 35.69 2.90 32.79
568.30 39.47 2.92 36.55
568.70 42.89 2.93 39.95
569.10 46.04 2.95 43.09
569.50 48.98 2.97 46.02
569.90 51.75 2.98 48.77
570.30 54.37 3.00 51.37
570.70 56.86 3.01 53.85
571.10 59.24 3.02 56.22
571.50 61.53 3.04 58.49
571.90 63.73 3.05 60.68
572.30 65.86 3.07 62.79
572.70 67.91 3.08 64.83
573.10 69.91 3.10 66.81
573.50 71.84 3.11 68.73
573.90 73.73 3.13 70.60
574.30 75.57 3.14 72.42
574.70 77.36 3.16 74.20
575.10 79.11 3.17 75.94
575.50 80.82 3.18 77.64
575.90 82.49 3.20 79.30
576.30 84.13 3.21 80.92
576.70 85.74 3.23 82.52
577.10 87.32 3.24 84.08
577.50 88.87 3.25 85.62
577.90 90.39 3.27 87.13
578.30 91.89 3.28 88.61
578.70 93.36 3.29 90.07
579.10 94.81 3.31 91.50
579.50 96.24 3.32 92.92
579.90 97.64 3.34 94.31
580.30 99.03 3.35 95.68
580.70 100.40 3.36 97.03
581.10 101.74 3.38 98.37
581.50 103.07 3.39 99.68
581.90 104.38 3.40 100.98
582.30 105.68 3.42 102.26
582.70 106.96 3.43 103.53
Elevation
(feet)
Discharge
(cfs)
Primary
(cfs)
Secondary
(cfs)
583.10 108.22 3.44 104.78
583.50 109.47 3.45 106.02
583.90 110.71 3.47 107.24
584.30 111.93 3.48 108.45
584.70 113.14 3.49 109.64
585.10 114.33 3.51 110.83
585.50 115.51 3.52 112.00
585.90 116.69 3.53 113.15
586.30 117.84 3.54 114.30
586.70 118.99 3.56 115.43
587.10 120.13 3.57 116.56
587.50 121.25 3.58 117.67
587.90 122.37 3.59 118.77
588.30 123.47 3.61 119.86
588.70 124.57 3.62 120.95
589.10 125.65 3.63 122.02
589.50 126.73 3.64 123.08
589.90 127.79 3.66 124.14
590.30 128.85 3.67 125.18
590.70 129.90 3.68 126.22
591.10 130.94 3.69 127.25
591.50 131.97 3.70 128.27
591.90 133.00 3.72 129.28
592.30 134.01 3.73 130.28
592.70 135.02 3.74 131.28
593.10 136.02 3.75 132.27
593.50 137.02 3.76 133.25
593.90 138.00 3.78 134.23
594.30 138.98 3.79 135.19
594.70 139.95 3.80 136.15
595.10 140.92 3.81 137.11
595.50 141.88 3.82 138.05
595.90 142.83 3.84 139.00
596.30 143.78 3.85 139.93
596.70 144.72 3.86 140.86
597.10 145.65 3.87 141.78
597.50 146.58 3.88 142.70
597.90 147.50 3.89 143.61
598.30 148.42 3.91 144.51
598.70 149.33 3.92 145.41
599.10 150.23 3.93 146.30
599.50 151.13 3.94 147.19
599.90 152.03 3.95 148.07
600.30 152.91 3.96 148.95
600.70 153.80 3.97 149.82
601.10 154.68 3.98 150.69
601.50 155.55 4.00 151.55
601.90 156.42 4.01 152.41
602.30 157.28 4.02 153.26
602.70 158.14 4.03 154.11