YADKI-044 Final Report

DAM HYDRAULIC CAPACITY
ASSESSMENT REPORT
(DRAFT)

DAVIS DAM

YADKI-044

YADKIN COUNTY, NC

PREPARED BY:
HDR Engineering Inc. of the Carolinas

2020

EXECUTIVE SUMMARY
A hydraulic capacity analysis was completed for the Davis Dam in Yadkin 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 not
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 =
518.6
418.5
434.3
450.4
466.9
483.8
501.0
795.9
796.4
796.9
797.4
797.9
ELEVATION
793.4
793.9
794.4
794.9
795.4
36.7
42.8
49.0
STORAGE (ACRE-FT)
0.0
4.8
9.6
14.5
19.6
25.1
30.8
777.4
774.4
774.9
775.4
775.9
776.4
776.9
772.9
NA
ELEVATION
772.9
773.4
773.9
STORAGE (ACRE-FT)
373.2
387.9
403.0
72.91
29
SCS Type 2
SPILLWAY
Primary
Auxiliary
TYPE
Riser / Barrel
NA
ELEVATION
24 HOUR - 100 YEAR EVENT, 7.61 INCHES, ELEVATION 777.6 (1 FT OVER-TOPPED)
24 HOUR - 50 YEAR EVENT, 6.79 INCHES, ELEVATION 777.3 (0.7 FT OVER-TOPPED)
24 HOUR - 25 YEAR EVENT, 5.99 INCHES, ELEVATION 776.8 (0.2 FT OVER-TOPPED)
TOP OF DAM ELEVATION = 776.6
SUMMARY OF INPUT PARAMETERS
0.41
SUMMARY SHEET OF HYDRAULIC CAPACITY RESULTS
DAVIS DAM, YADKI-044
ANALYSIS PERFORMED BY: S. MURPHY, HDR
24 HOUR - 1000 YEAR EVENT, 10.6 INCHES, ELEVATION 778.5 (1.9 FT OVER-TOPPED)
24 HOUR - 500 YEAR EVENT, 9.65 INCHES, ELEVATION 778.3 (1.7 FT OVER-TOPPED)
24 HOUR - 200 YEAR EVENT, 8.46 INCHES, ELEVATION 777.9 (1.3 FT OVER-TOPPED)
YADKI-044DAVIS DAM DECEMBER 3, 2020
1232.9
NOT TO SCALE
1059.2
1087.0
1115.2
1143.9
1173.1
1202.8
901.8
926.9
952.5
978.5
1004.9
1031.8
759.8
782.4
805.5
828.9
852.8
877.1
632.3
652.6
673.2
694.3
715.7
737.5
536.6
554.9
573.6
592.8
612.3
810.9
811.4
811.9
812.4
812.9
807.9
808.4
808.9
809.4
809.9
810.4
804.9
805.4
805.9
806.4
806.9
807.4
801.9
802.4
802.9
803.4
803.9
804.4
798.9
799.4
799.9
800.4
800.9
801.4
798.4
317.3
330.8
344.6
358.7
242.9
254.5
266.4
278.6
291.2
304.1
178.8
188.9
199.2
209.7
220.5
231.5
123.5
132.1
141.0
150.1
159.4
169.0
76.1
83.4
91.0
98.8
106.8
115.0
55.5
62.1
69.0
792.4
792.9
789.4
789.9
790.4
790.9
791.4
791.9
786.4
786.9
787.4
787.9
788.4
788.9
783.4
783.9
784.4
784.9
785.4
785.9
780.4
780.9
781.4
781.9
782.4
782.9
777.9
778.4
778.9
779.4
779.9
YADKI-044DAVIS DAM DECEMBER 3, 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
Davis Dam - YADKI-044 - Watershed Boundary
Legend
Longest FlowPath
Watershed Bound ary
0 0.25 0.50.125 Miles
Date: 10 /5/2020
/Drainage Area: 0.41 Square MilesFlowpath Length: 1.1 miles

APPENDIX B

Lag Time Calculation
Dam No:YADKI-044 Date:10/26/2020
Dam Name:Davis 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 =72.9067 from NRCS CN Calculation
S =3.71616 in.
Mean Basin Slope Y =10.6581 %from Watershed Mean slope
Longest Flowpath:1.08 mi.from Watershed Longest flowpath
Flow Length l =5702.4 ft.
Time of Concentration Tc =0.80 Hours Tc =48 mins
Lag Time TL =0.48 Hours TL =29 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 67764 100 6776419 5140 100 514043 227401 100 22740066
Developed, Open Space Open space - Fair condition (grass cover 50% to 75%)0 49 0 372077 69 25673289 333242 79 26326120 138306 84 11617682
Developed, Low Intensity Residential districts by average lot size: 1/3 acre 0 57 0 23462 72 1689230 53429 81 4327747 15288 86 1314731
Developed, Medium Intensity Residential districts by average lot size: 1/8 acre 0 77 0 0 85 0 0 90 0 0 92 0
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 1961836 60 117710158 432248 73 31554081 2168142 79 171283204
Evergreen Forest Woods - Fair 0 36 0 467675 60 28060496 378302 73 27616058 500436 79 39534432
Mixed Forest Woods - Fair 0 36 0 682849 60 40970927 208550 73 15224120 672997 79 53166772
Shrub/Scrub Brush - Fair 0 35 0 0 56 0 2268 70 158727 0 77 0
Herbaceuous Herbaceuous - Fair 0 60 0 104148 71 7394526 1156 81 93636 19375 89 1724332
Hay/Pasture Pasture - Fair 0 49 0 923349 69 63711107 1083298 79 85580528 517942 84 43507146
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=72.91
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): Yadkinville, North Carolina USA
Station Name: -
Latitude: 36.128933°
Longitude: -80.562771°
Elevation (USGS): 826.1 ft
PRECIPITATION FREQUENCY ESTIMATES
by
duration
for ARI
(years):1 2 5 10 25 50 100 200 500 1000
5-min:0.359 0.425 0.502 0.556 0.62 0.665 0.705 0.743 0.786 0.816
10-min:0.574 0.68 0.804 0.89 0.989 1.06 1.12 1.18 1.24 1.29
15-min:0.717 0.855 1.02 1.13 1.25 1.34 1.42 1.49 1.56 1.61
30-min:0.983 1.18 1.45 1.63 1.86 2.02 2.17 2.31 2.49 2.61
60-min:1.23 1.48 1.85 2.12 2.47 2.74 2.99 3.24 3.57 3.81
2-hr:1.44 1.75 2.2 2.54 3 3.35 3.69 4.05 4.52 4.87
3-hr:1.55 1.88 2.37 2.75 3.26 3.66 4.06 4.48 5.04 5.48
6-hr:1.9 2.31 2.9 3.37 4 4.52 5.04 5.57 6.31 6.88
12-hr:2.3 2.79 3.52 4.09 4.89 5.53 6.19 6.89 7.85 8.61
24-hr:2.8 3.39 4.29 5.01 5.99 6.79 7.61 8.46 9.65 10.6
2-day:3.29 3.96 4.97 5.76 6.82 7.67 8.54 9.42 10.6 11.6
3-day:3.5 4.21 5.26 6.07 7.17 8.05 8.95 9.87 11.1 12.1
4-day:3.71 4.46 5.54 6.38 7.52 8.43 9.36 10.3 11.6 12.6
7-day:4.24 5.07 6.18 7.05 8.21 9.13 10.1 11 12.3 13.3
10-day:4.85 5.78 6.96 7.87 9.07 10 11 11.9 13.2 14.1
20-day:6.52 7.71 9.13 10.2 11.7 12.8 14 15.1 16.6 17.8
30-day:8.09 9.53 11 12.1 13.5 14.6 15.7 16.7 18 19
45-day:10.2 11.9 13.6 14.8 16.3 17.5 18.6 19.7 21 22
60-day:12.2 14.2 16 17.3 19 20.3 21.5 22.6 24.1 25.1
Date/time (GMT): Mon Oct 26 20:44:36 2020
pyRunTime: 0.0152099132538

APPENDIX F
Outlet Works Rating Curves

Total outlet discharge from the spillway system
Client:NCEM Date:10/26/2020
Project:Overtopping Study Engineer:T.Carter
Dam:Davis Dam Dam No.YADKI-044
Reservior Water
Level (RWS)
Elevation (ft)
Total discharge from the
spillway system (cfs)
(from Hydrocad)
772.9 0.0
773.7 3.6
774.5 13.0
775.3 25.2
776.1 35.0
776.9 42.5
777.7 48.8
778.5 54.4
779.3 59.5
780.1 64.2
780.9 68.5
781.7 72.6
782.5 76.5
783.3 80.2
784.1 83.7
784.9 87.1
785.7 90.3
786.5 93.5
787.3 96.5
788.1 99.5
788.9 102.3
789.7 105.1
790.5 107.8
791.3 110.5
792.1 113.0
792.9 115.6
793.7 118.0
794.5 120.5
795.3 122.8
796.1 125.2
796.9 127.5
797.7 129.7
798.5 131.9
799.3 134.1
800.1 136.2
800.9 138.3
801.7 140.4
802.5 142.4
803.3 144.5
804.1 146.4
804.9 148.4
805.7 150.3
806.5 152.2
807.3 154.1
808.1 156.0
808.9 157.8
809.7 159.6
0.0
20.0
40.0
60.0
80.0
100.0
120.0
140.0
160.0
180.0
770.0 775.0 780.0 785.0 790.0 795.0 800.0 805.0 810.0 815.0Total discharge from the spillway system (cfs)Reservior Water Level (RWS) Elevation (ft)
The whole spillway system rating curve (cfs)
Yadki-044 Davis Dam
Rainfall not specifiedYADKI-044
Printed 12/3/2020Prepared by HDR, Inc
Page 1HydroCAD® 10.00-25 s/n 07102 © 2019 HydroCAD Software Solutions LLC
Summary for Pond 1P: YADKI-044 Davis Dam
Volume Invert Avail.Storage Storage Description
#1 772.90' 53,716,839 cf Custom Stage Data (Prismatic) Listed below (Recalc)
Yadki-044 Davis Dam
Rainfall not specifiedYADKI-044
Printed 12/3/2020Prepared 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)
772.90 428,486 0 0
773.40 428,486 214,243 214,243
773.90 428,486 214,243 428,486
774.40 428,486 214,243 642,729
774.90 466,797 223,821 866,550
775.40 487,891 238,672 1,105,222
775.90 504,541 248,108 1,353,330
776.40 519,863 256,101 1,609,431
776.90 535,664 263,882 1,873,313
777.40 552,881 272,136 2,145,449
777.90 570,752 280,908 2,426,357
778.40 589,287 290,010 2,716,367
778.90 609,717 299,751 3,016,118
779.40 629,023 309,685 3,325,803
779.90 648,740 319,441 3,645,244
780.40 667,490 329,058 3,974,301
780.90 687,744 338,809 4,313,110
781.40 706,904 348,662 4,661,772
781.90 726,328 358,308 5,020,080
782.40 745,830 368,040 5,388,119
782.90 764,658 377,622 5,765,741
783.40 783,652 387,078 6,152,819
783.90 803,135 396,697 6,549,515
784.40 823,291 406,607 6,956,122
784.90 844,043 416,834 7,372,955
785.40 865,225 427,317 7,800,272
785.90 885,654 437,720 8,237,992
786.40 907,041 448,174 8,686,166
786.90 928,760 458,950 9,145,116
787.40 950,771 469,883 9,614,999
787.90 974,775 481,387 10,096,385
788.40 999,912 493,672 10,590,057
788.90 1,025,117 506,257 11,096,314
789.40 1,051,436 519,138 11,615,453
789.90 1,079,961 532,849 12,148,302
790.40 1,108,008 546,992 12,695,294
790.90 1,135,234 560,811 13,256,105
791.40 1,164,072 574,827 13,830,931
791.90 1,190,039 588,528 14,419,459
792.40 1,216,846 601,721 15,021,180
792.90 1,243,975 615,205 15,636,385
793.40 1,272,256 629,058 16,265,443
793.90 1,301,309 643,391 16,908,834
794.40 1,330,869 658,045 17,566,879
794.90 1,360,635 672,876 18,239,755
795.40 1,391,270 687,976 18,927,731
795.90 1,423,223 703,623 19,631,354
796.40 1,454,297 719,380 20,350,734
796.90 1,484,385 734,671 21,085,405
Yadki-044 Davis Dam
Rainfall not specifiedYADKI-044
Printed 12/3/2020Prepared by HDR, Inc
Page 3HydroCAD® 10.00-25 s/n 07102 © 2019 HydroCAD Software Solutions LLC
797.40 1,515,820 750,051 21,835,456
797.90 1,547,178 765,750 22,601,206
798.40 1,579,590 781,692 23,382,898
798.90 1,614,463 798,513 24,181,411
799.40 1,649,658 816,030 24,997,441
799.90 1,686,504 834,041 25,831,482
800.40 1,720,713 851,804 26,683,286
800.90 1,752,676 868,347 27,551,633
801.40 1,784,385 884,265 28,435,898
801.90 1,816,260 900,161 29,336,060
802.40 1,849,766 916,507 30,252,566
802.90 1,884,570 933,584 31,186,150
803.40 1,919,541 951,028 32,137,178
803.90 1,955,137 968,670 33,105,847
804.40 1,989,932 986,267 34,092,115
804.90 2,024,668 1,003,650 35,095,765
805.40 2,060,498 1,021,292 36,117,056
805.90 2,096,934 1,039,358 37,156,414
806.40 2,134,258 1,057,798 38,214,212
806.90 2,171,182 1,076,360 39,290,572
807.40 2,208,984 1,095,042 40,385,614
807.90 2,246,318 1,113,826 41,499,439
808.40 2,284,541 1,132,715 42,632,154
808.90 2,323,193 1,151,934 43,784,087
809.40 2,362,656 1,171,462 44,955,550
809.90 2,401,963 1,191,155 46,146,704
810.40 2,441,885 1,210,962 47,357,666
810.90 2,482,051 1,230,984 48,588,650
811.40 2,522,031 1,251,021 49,839,671
811.90 2,563,828 1,271,465 51,111,136
812.40 2,605,518 1,292,337 52,403,472
812.90 2,647,949 1,313,367 53,716,839
Device Routing Invert Outlet Devices
#1 Primary 772.90'36.0" Round 36" HDPE
L= 40.0' CPP, projecting, no headwall, Ke= 0.900
Inlet / Outlet Invert= 772.90' / 770.20' S= 0.0675 '/' Cc= 0.900
n= 0.020, Flow Area= 7.07 sf
Primary OutFlow Max=0.00 cfs @ 5.00 hrs HW=0.00' (Free Discharge)
1=36" HDPE ( Controls 0.00 cfs)
Yadki-044 Davis Dam
Rainfall not specifiedYADKI-044
Printed 12/3/2020Prepared by HDR, Inc
Page 4HydroCAD® 10.00-25 s/n 07102 © 2019 HydroCAD Software Solutions LLC
Stage-Discharge for Pond 1P: YADKI-044 Davis Dam
Elevation
(feet)
Primary
(cfs)
772.90 0.00
773.30 0.95
773.70 3.64
774.10 7.77
774.50 13.04
774.90 19.03
775.30 25.24
775.70 30.88
776.10 35.03
776.50 38.94
776.90 42.48
777.30 45.76
777.70 48.81
778.10 51.69
778.50 54.41
778.90 57.00
779.30 59.48
779.70 61.86
780.10 64.15
780.50 66.36
780.90 68.50
781.30 70.58
781.70 72.60
782.10 74.56
782.50 76.47
782.90 78.34
783.30 80.16
783.70 81.94
784.10 83.69
784.50 85.39
784.90 87.07
785.30 88.71
785.70 90.32
786.10 91.91
786.50 93.47
786.90 95.00
787.30 96.51
787.70 97.99
788.10 99.45
788.50 100.90
788.90 102.32
789.30 103.72
789.70 105.10
790.10 106.47
790.50 107.81
790.90 109.15
791.30 110.46
791.70 111.76
792.10 113.04
792.50 114.32
792.90 115.57
Elevation
(feet)
Primary
(cfs)
793.30 116.81
793.70 118.04
794.10 119.26
794.50 120.47
794.90 121.66
795.30 122.84
795.70 124.01
796.10 125.17
796.50 126.32
796.90 127.45
797.30 128.58
797.70 129.70
798.10 130.81
798.50 131.91
798.90 133.00
799.30 134.08
799.70 135.15
800.10 136.22
800.50 137.27
800.90 138.32
801.30 139.36
801.70 140.39
802.10 141.42
802.50 142.44
802.90 143.45
803.30 144.45
803.70 145.44
804.10 146.43
804.50 147.42
804.90 148.39
805.30 149.36
805.70 150.33
806.10 151.28
806.50 152.24
806.90 153.18
807.30 154.12
807.70 155.06
808.10 155.98
808.50 156.91
808.90 157.82
809.30 158.74
809.70 159.64
810.10 160.55
810.50 161.44
810.90 162.33
811.30 163.22
811.70 164.10
812.10 164.98
812.50 165.85
812.90 166.72