ROWAN-025 Final Report

DAM HYDRAULIC CAPACITY
ASSESSMENT REPORT
(DRAFT)

LANDIS LAKE DAM

ROWAN-025

ROWAN 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 Landis Lake Dam in Rowan 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, and 100 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 =
1358.8
1019.3
1072.5
1127.0
1182.8
1240.0
1298.7
789.0
789.5
790.0
790.5
791.0
53.4
62.6
72.1
ELEVATION
786.5
787.0
787.5
788.0
788.5
770.5
767.5
768.0
768.5
769.0
769.5
770.0
766.0
NA
ELEVATION
766.0
766.5
767.0
STORAGE (ACRE-FT)
867.7
916.9
967.5
STORAGE (ACRE-FT)
0.0
6.7
13.6
20.9
28.4
36.3
44.7
70.75
95
SCS Type 2
SPILLWAY
Primary
Auxiliary
TYPE
Gravel Lined Trapazoidal Spillway
NA
ELEVATION
SUMMARY OF INPUT PARAMETERS
2.19
SUMMARY SHEET OF HYDRAULIC CAPACITY RESULTS
LANDIS LAKE DAM, ROWAN-025
ANALYSIS PERFORMED BY: S. MURPHY, HDR
TOP OF DAM ELEVATION = 769
24 HOUR - 100 YEAR EVENT, 7.3 INCHES, ELEVATION 769 (0 FT FREE-BOARD)
24 HOUR - 50 YEAR EVENT, 6.55 INCHES, ELEVATION 768.7 (0.3 FT FREE-BOARD)
24 HOUR - 25 YEAR EVENT, 5.82 INCHES, ELEVATION 768.5 (0.5 FT FREE-BOARD)
24 HOUR - 1000 YEAR EVENT, 9.95 INCHES, ELEVATION 769.3 (0.3 FT OVER-TOPPED)
24 HOUR - 500 YEAR EVENT, 9.12 INCHES, ELEVATION 769.2 (0.2 FT OVER-TOPPED)
24 HOUR - 200 YEAR EVENT, 8.07 INCHES, ELEVATION 769.1 (0.1 FT OVER-TOPPED)
ROWAN-025LANDIS LAKE DAM SEPTEMBER 10, 2020
4073.4
NOT TO SCALE
3369.7
3480.7
3594.2
3710.2
3828.6
3949.6805.5
806.0
819.8
785.5
786.0
783.0
783.5
784.0
784.5
785.0
804.0
804.5
805.0684.9
2751.6
2848.9
2948.5
3050.3
3154.5
3261.0
2216.3
2299.8
2385.6
2473.7
2563.9
2656.6
1901.9
1977.7
2055.4
2134.9
1420.5
1484.0
1549.2
1616.2
1685.0
801.0
801.5
802.0
802.5
803.0
803.5
792.0
792.5
793.0
793.5
794.0
794.5
796.5
797.0
797.5
798.0
798.5
799.0
799.5
800.0
800.5
795.0
795.5
796.0
1755.5
1827.8
791.5
728.4
773.3
563.2
602.4
642.9
148.4
160.6
173.2
82.0
92.2
102.8
454.0
489.0
525.5
273.8
299.2
328.6
358.4
388.9
420.7
186.2
199.7
213.7
228.1
242.9
258.1
113.7
124.9
136.5
782.5
779.5
780.0
780.5
781.0
781.5
782.0
776.5
777.0
777.5
778.0
778.5
779.0
775.0
775.5
776.0
771.0
771.5
772.0
772.5
773.0
773.5
774.0
774.5
ROWAN-025LANDIS LAKE DAM SEPTEMBER 10, 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
Landis Lake Dam - ROWAN-025 - Watershed Boundary
Legend
LongestFlowPath
WatershedBoundary
0 0.5 10.25 Miles
Date: 9/9/2020
/Drainage Area: 2.19 Square MilesFlowpath Length: 15684.7 feet

APPENDIX B

Lag Time Calculation
Dam No:ROWAN-025 Date:9/4/2020
Dam Name:Landis 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 =70.7524 from NRCS CN Calculation
S =4.13381 in.
Mean Basin Slope Y =5.65007 %from Watershed Mean slope
Longest Flowpath:2.97059 mi.from Watershed Longest flowpath
Flow Length l =15684.7 ft.
Time of Concentration Tc =2.63 Hours Tc =158 mins
Lag Time TL =1.58 Hours TL =95 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 163740 100 16374042 58785 100 5878473 1238437 100 123843657
Developed, Open Space Open space - Fair condition (grass cover 50% to 75%)0 49 0 9455884 69 652455962 4473453 79 353402801 566187 84 47559692
Developed, Low Intensity Residential districts by average lot size: 1/3 acre 0 57 0 2449259 72 176346681 2152572 81 174358306 125012 86 10751068
Developed, Medium Intensity Residential districts by average lot size: 1/8 acre 0 77 0 245583 85 20874543 580515 90 52246370 0 92 0
Developed, High Intensity Urban districts - Commercial and business 0 89 0 8235 92 757649 328115 94 30842795 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 10226252 60 613575136 1890347 73 137995332 464800 79 36719176
Evergreen Forest Woods - Fair 0 36 0 3398325 60 203899475 857593 73 62604259 30429 79 2403897
Mixed Forest Woods - Fair 0 36 0 2331935 60 139916122 656746 73 47942448 91244 79 7208287
Shrub/Scrub Brush - Fair 0 35 0 0 56 0 0 70 0 0 77 0
Herbaceuous Herbaceuous - Fair 0 60 0 154473 71 10967563 156090 81 12643264 34472 89 3067970
Hay/Pasture Pasture - Fair 0 49 0 12428606 69 857573780 3540703 79 279715534 296130 84 24874887
Cultivated Crops Row crops (SR + CR) - Poor 0 71 0 2442013 80 195361023 174346 87 15168113 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=70.75
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): China Grove, North Carolina USA
Station Name: -
Latitude: 35.5638°
Longitude: -80.602°
Elevation (USGS): 763.13 ft
PRECIPITATION FREQUENCY ESTIMATES
by
duration
for ARI
(years):1 2 5 10 25 50 100 200 500 1000
5-min:0.389 0.46 0.537 0.591 0.652 0.694 0.731 0.764 0.799 0.824
10-min:0.622 0.736 0.86 0.945 1.04 1.1 1.16 1.21 1.27 1.3
15-min:0.777 0.925 1.09 1.2 1.32 1.4 1.47 1.53 1.59 1.63
30-min:1.07 1.28 1.55 1.73 1.95 2.11 2.25 2.38 2.53 2.64
60-min:1.33 1.6 1.98 2.26 2.6 2.85 3.1 3.34 3.63 3.85
2-hr:1.54 1.86 2.31 2.65 3.09 3.42 3.75 4.07 4.49 4.8
3-hr:1.64 1.98 2.47 2.85 3.35 3.74 4.13 4.53 5.06 5.47
6-hr:1.99 2.4 3 3.46 4.08 4.58 5.08 5.59 6.28 6.82
12-hr:2.36 2.84 3.56 4.13 4.91 5.54 6.18 6.85 7.77 8.49
24-hr:2.79 3.37 4.23 4.9 5.82 6.55 7.3 8.07 9.12 9.95
2-day:3.25 3.92 4.88 5.64 6.66 7.47 8.29 9.14 10.3 11.2
3-day:3.46 4.16 5.15 5.93 7 7.84 8.7 9.58 10.8 11.7
4-day:3.66 4.39 5.42 6.23 7.34 8.21 9.11 10 11.3 12.3
7-day:4.22 5.04 6.13 7 8.19 9.13 10.1 11.1 12.4 13.5
10-day:4.83 5.74 6.9 7.81 9.02 9.97 10.9 11.9 13.2 14.2
20-day:6.49 7.66 9.04 10.1 11.6 12.7 13.9 15.1 16.6 17.8
30-day:8.01 9.43 10.9 12.1 13.7 14.8 16 17.2 18.7 19.9
45-day:10.1 11.8 13.5 14.8 16.4 17.7 18.9 20.1 21.6 22.8
60-day:12 14 15.8 17.2 19 20.3 21.6 22.9 24.5 25.7
Date/time (GMT): Fri Aug 28 16:03:59 2020
pyRunTime: 0.0159440040588

APPENDIX F
Outlet Works Rating Curves

Total outlet discharge from the spillway system
Client:NCEM Date:9/8/2020
Project:Overtopping Study Engineer:E.Torrey
Dam:Landis Lake Dam Dam No.ROWAN-025
Reservior Water
Level (RWS)
Elevation (ft)
Primary spillway
discharge (cfs)
Emergency spillway
discharge (cfs)
Total discharge from the
spillway system (cfs)
766.0 0.0 0.0 0.0
766.5 35.2 0.0 35.2
767.0 137.0 0.0 137.0
767.5 320.6 0.0 320.6
768.0 599.6 0.0 599.6
768.5 986.2 0.0 986.2
769.0 1491.3 0.0 1491.3
769.5 2124.8 0.0 2124.8
770.0 2896.0 0.0 2896.0
770.5 3813.6 0.0 3813.6
771.0 4885.8 0.0 4885.8
771.5 6120.4 0.0 6120.4
772.0 7524.8 0.0 7524.8
772.5 9106.2 0.0 9106.2
773.0 10871.4 0.0 10871.4
773.5 12827.0 0.0 12827.0
774.0 14979.4 0.0 14979.4
774.5 17334.7 0.0 17334.7
775.0 19899.0 0.0 19899.0
775.5 22678.1 0.0 22678.1
776.0 25677.7 0.0 25677.7
776.5 28903.3 0.0 28903.3
777.0 32360.3 0.0 32360.3
777.5 36054.0 0.0 36054.0
778.0 39989.6 0.0 39989.6
778.5 44172.1 0.0 44172.1
779.0 48606.4 0.0 48606.4
779.5 53297.5 0.0 53297.5
780.0 58250.1 0.0 58250.1
780.5 63468.9 0.0 63468.9
781.0 68958.5 0.0 68958.5
781.5 74723.4 0.0 74723.4
782.0 80768.0 0.0 80768.0
782.5 87096.8 0.0 87096.8
783.0 93714.1 0.0 93714.1
783.5 100624.1 0.0 100624.1
784.0 107831.0 0.0 107831.0
784.5 115338.9 0.0 115338.9
785.0 123152.0 0.0 123152.0
785.5 131274.2 0.0 131274.2
786.0 139709.5 0.0 139709.5
786.5 148461.9 0.0 148461.9
787.0 157535.2 0.0 157535.2
787.5 166933.2 0.0 166933.2
788.0 176659.8 0.0 176659.8
0.0
20000.0
40000.0
60000.0
80000.0
100000.0
120000.0
140000.0
160000.0
180000.0
200000.0
760.0 765.0 770.0 775.0 780.0 785.0 790.0Total discharge from the spillway system (cfs)Reservior Water Level (RWS) Elevation (ft)
The whole spillway system rating curve (cfs)