These regulations are adopted under the authority conferred on the City by the General Assembly of the State of Arkansas by A.C.A. § 14-56-401 et seq.
The purpose of this section is to protect, maintain, and enhance the health, safety, and welfare of the public by:
A. 
Preventing increases in the magnitude and frequency of stormwater runoff to prevent increases in flood flows and associated hazards and costs;
B. 
Controlling soil erosion and sedimentation to minimize soil deposition in streams, lakes, and other receiving water bodies and storm drainage systems; and
C. 
Requiring surface and stormwater management practices that comply with the provisions of this section.
The City hereby adopts by reference the current edition of the Federal Highway Administration Urban Drainage Design Manual except as modified herein. All drainage technical procedures and design standards contained therein shall have the same force and effect as if printed word for word in this section.
The provisions of this section shall apply to all land within the corporate limits and territorial jurisdiction (also known as Planning Area Map) of the City, as they now or may hereafter exist. These regulations shall also apply to any land annexed into the corporate limits after adoption of these regulations.
A. 
General. All plans and technical reports submitted for review under this section shall be stamped by a registered professional engineer or licensed landscape architect, licensed to practice in the State of Arkansas.
B. 
Conceptual review. A conceptual stormwater drainage and management plan review with City staff is encouraged before initiation of other permitting that may be required under this or other City codes.
C. 
Preliminary submittal. Preliminary plans and technical reports required herein shall be submitted at the same time as a site plan, large-scale development, preliminary plat, are submitted. If needed, a review meeting will be scheduled by City staff with a representative of the developer, including the design professional, to review the concepts presented in the plans and technical reports. The purpose of the meeting is to jointly agree to an overall stormwater concept for the proposed development and to review criteria and design parameters that shall apply to the final design of the project.
D. 
Final submittal. Following the preliminary plans and technical reports, final plans and technical reports shall be prepared for each phase of the proposed project. The final plan shall constitute a refinement of the concepts approved in the preliminary plans with preparation and submittal of detailed information as required in the Urban Drainage Design Manual.
A. 
A technical drainage report shall be required that is prepared by a registered professional engineer or licensed landscape architect, licensed to practice in the State of Arkansas, describing the assumptions, calculations, and procedures used for determining compliance with the Urban Drainage Design Manual.
B. 
The following items shall be included in the drainage report that accompanies each proposed improvement plan set submitted to the City.
(1) 
Aerial photograph. Aerial photograph of the project vicinity, covering the project area and the totals lands that contribute runoff.
(2) 
Topographic map. Topographic map of the project showing the location and elevation of benchmarks, including at least one benchmark for each control structure.
(3) 
Soils and vegetation map. Soils and vegetation map displaying the most recent U.S. Soil Conservation Service information and encompassing both the project area and the drainage area that contributes runoff.
(4) 
Existing and proposed improvements. Plans detailing existing and proposed building and pavement locations, proposed grading and drainage improvements, as well as supplemental details showing drainage release structures and stormwater conveyance systems.
(5) 
Erosion control drawings. Plans identifying the type, location, and schedule for implementing erosion and sediment control measures, including appropriate provisions for maintenance and disposition of temporary measures.
(a) 
Project title and date;
(b) 
Project location: include the street address and a vicinity map;
(c) 
Project description: a brief description of the proposed project;
(d) 
Project owner's name, address and telephone number;
(e) 
Site area: to the nearest 0.1 acre;
(f) 
Site drainage: a brief description of the site drainage for the proposed project;
(g) 
Area drainage problems: provide a description of any known on-site, downstream or upstream drainage/flooding problems;
(h) 
Upstream and downstream drainage: a) pre- and post-developed drainage area maps as well as inlet area maps with the time of concentration flow paths and b) proposed and existing topography shown as appropriate;
(i) 
Summary of runoff: provide a table with the one-, two-, five-, ten-, twenty-five-, fifty-, and 100-year storm flows for existing and proposed conditions (with and without detention if shown) and the proposed difference in flows;
(j) 
Calculations: provide copies of all calculations performed, including:
1. 
Runoff flow calculations for the one-, two-, five-, ten-, twenty-five-, fifty-, and 100-year storm events (existing and proposed conditions);
2. 
Coefficients or runoff curve numbers;
3. 
Inlet calculations, include any ponded area created at each;
4. 
Pipe or culvert calculations;
5. 
Open-channel calculations including any flumes;
6. 
Detention calculations including:
i. 
Basin sizing calculations;
ii. 
Outlet structure design with release rates computations for the one-, two-, five-, ten-, twenty-five-, fifty-, and 100-year storm events;
iii. 
Stage-storage and stage-discharge curves; and
(k) 
Hydraulic grade line calculations.
(6) 
Recommendations/summary: description of any assumptions made in the calculations, drainage improvements to be made to the site and the expected effects of the project.
(7) 
Certification. All drainage reports shall be signed, sealed and dated by an engineer registered in the State of Arkansas and shall include the following certification:
"I__________________, Registered Professional Engineering No. _____ in the State of Arkansas, hereby certify that the drainage designs and specifications contained in this Report have been prepared by me, or under my responsible supervision, in accordance with the regulations of the City of Lincoln, Arkansas, the Professional Engineers Registration Act of the State of Arkansas, and reflect the application of generally accepted standards of Engineering practice. I further certify that the improvements outlined in this Report will not have any adverse effects to life or downstream properties. I understand that review of these plans is limited to general compliance with the City codes and regulations and does not warrant the Engineer's design or imply any liability to the City of Lincoln for the designs contained herein."
Except as otherwise provided in this section, a development must be designed, constructed, operated, and maintained to comply with the following criteria:
A. 
Peak discharge. The post-development peak rate of surface discharge must not exceed the existing peak rate of surface discharge for twenty-four-hour duration storms for the one-, two-, five-, ten-, twenty-five-, fifty-, and 100-year events. Exceptions may be granted if the applicant can conclusively demonstrate, as determined by City staff, that there is a negligible impact downstream by increased peak flows.
B. 
Direct discharge. Direct discharge of a pipe into streams and/or floodways is not allowed. A stilling basin or other structure that will collect sediment, trash, etc. and that will reduce the likelihood of erosion into the receiving stream due to discharge from the pipe shall be installed at pipe discharges into streams and/or floodways.
C. 
Erosion and channel stability. All stormwater management systems shall be evaluated on their ability to prevent erosion and sedimentation into receiving waters and adverse impacts on the site's natural systems. The design professional shall consider the on-site and downstream effects of the peak discharges and shall design both the permanent and construction phase of the system in a manner that will not increase flooding, channel instability, or erosion downstream when considered in aggregate with other developed properties and downstream drainage capacities.
D. 
Drainage into wetlands and floodways. Areas defined as wetlands and floodways by the appropriate federal agencies shall be protected from adverse change in runoff quantity and quality from associated land development.
E. 
Precipitation data and rainfall intensity. The following tables shall be used to estimate stormwater runoff utilizing appropriate methods as provided in the Urban Drainage Design Manual.
Table 1
Rainfall Intensities (inches per hour)
Tc
(min)
Return Period
5
15
30
60
2-year
5.44
3.47
2.42
1.63
5-year
6.68
4.31
3.03
2.06
10-year
7.56
4.90
3.46
2.36
25-year
8.85
5.75
4.07
2.79
50-year
9.84
6.40
4.54
3.12
100-year
10.83
7.07
5.02
3.45
Table 2
Intensity-Duration-Frequency Curve Coefficients
(inches per hour)
Variable
Return Period
B
D
E
1-year
0.000
0.000
0.000
2-year
23.629
4.900
0.641
5-year
27.686
4.800
0.623
10-year
30.844
4.800
0.616
25-year
35.311
4.700
0.609
50-year
38.983
4.700
0.606
100-year
42.641
4.700
0.603
Table 3
Twenty-Four-Hour Design Rainfall
(inches)
Duration
1-year
2-year
5-year
10-year
25-year
50-year
100-year
24 hours
3.50
3.92
4.65
5.31
6.27
7.07
7.91
F. 
Rational Method runoff coefficients. Table 3-1 of the Urban Drainage Design Manual shall be replaced with the following table:
Table 4
Runoff Coefficients for Various Land Uses
Land Use Description
Slope
(%)
Hydrologic Soil Group
B
C
D
Lawns
0-2
0.15
0.25
0.35
2-7
0.25
0.35
0.4
>7
0.3
0.35
0.45
Unimproved areas
Forest
0.15-.2
0.2-.25
0.2-0.3
Meadow
0.2-0.4
0.25-0.45
0.3-0.55
Row crops
0.25-0.6
0.35-0.75
0.4-0.8
Business
Downtown areas
0.7
0.8
0.9
Neighborhood areas
0.5
0.6
0.7
Residential
8 lots per acre
0.67
0.71
0.76
4 lots per acre
0.46
0.52
0.61
3 lots per acre
0.4
0.47
0.57
2 lots per acre
0.35
0.43
0.54
Suburban (1 lot per acre)
0.3
0.38
0.5
Multi-units, detached
0.7
0.75
0.8
Multi-units, attached
0.75
0.8
0.85
Apartments
0.65
0.7
0.75
Industrial
Light areas
0.6
0.75
0.85
Heavy areas
0.8
0.85
0.9
Parks, cemeteries
0.25
0.35
0.45
Schools, churches
0.7
0.75
0.8
Railroad yard areas
0.2
0.35
0.5
Asphalt and concrete pavements, roofs
0.95
Brick pavement or gravel (compacted subgrade)
0.85
Graded or no plant cover
0-2
0.25
0.3
0.35
2-7
0.35
0.45
0.55
>7
0.5
0.65
0.8
Table 5
Runoff Curve Numbers
Cover Description
Curve Numbers for Hydrologic Soil Groups
Cover Type and Hydrologic Condition2
Average Percent Impervious Area3
B
C
D
Cultivated land
Without conservation treatment
81
88
91
With conservation treatment
71
78
81
Pasture or range land
Poor condition
79
86
89
Good condition
61
74
80
Meadow
Good condition
58
71
78
Wood or forest land
Thin stand, poor cover
66
77
83
Good cover
55
70
77
Open space (lawns, parks, golf courses, cemeteries, etc.)4
Poor condition (grass cover <50%)
79
86
89
Fair condition (grass cover 50% to 75%)
69
79
84
Good condition (grass cover > 75%)
61
74
80
Impervious areas
Paved parking lots, roofs, driveways, etc. (excluding right-of-way)
98
98
98
Streets and roads
Paved; curbs and storm drains (excluding right-of-way)
98
98
98
Paved; open ditches (including right-of-way)
89
92
93
Gravel (including right-of-way)
85
89
91
Dirt (including right-of-way)
82
87
89
Urban districts
Commercial and business
85%
92
94
95
Industrial
72%
88
91
93
Residential districts by average lot size
1/8 acre or less (townhouses)
65%
85
90
92
1/4 acre
38%
75
83
87
1/3 acre
30%
72
81
86
1/2 acre
25%
70
80
85
1 acre
20%
68
79
84
2 acres
12%
65
77
82
Developing urban areas and newly graded areas (pervious areas only, no vegetation)
86
91
94
G. 
Allowable spread in street.
Table 6
Flow Spread Limits and Ponding Depths for Inlets
(10-year design storm)
Street Classification
Maximum Depth at Curb for 100-Year Design Storm
(feet)
Maximum Encroachment
Example Based on Given Street Width (normal typical section)
Local without on-street parking
0.5
Spread of water flowing in gutter shall be limited so that half of roadway width (F.O.C. to F.O.C.) remains clear.
- Street width (F.O.C. to F.O.C.) = 20 feet
- Required clear lane = 20 feet/2 = 10 feet
- Therefore: Street flow in each gutter < (20'-10')/2 = 5 feet
Local with on-street parking
0.5
Spread of water flowing in gutter shall be limited so that half of roadway width (F.O.C. to F.O.C.) remains clear.
- Street width (F.O.C. to F.O.C.) = 26 feet
- Required clear lane = 26 feet/2 = 13 feet
- Therefore: Street flow in each gutter < (26'-13')/2 = 6.5 feet
Downtown
0.5
Spread of water flowing in gutter shall be limited so that half of roadway width (F.O.C. to F.O.C.) remains clear.
- Street width (F.O.C. to F.O.C.) = 37 feet
- Required clear lane = 37 feet/2 = 18.5 feet
- Therefore: Street flow in each gutter < (37'-18.5')/2 = 9.25 feet
Collector with side path
0.5
- Spread of water flowing in gutter shall be limited so that half of roadway width (F.O.C. to F.O.C.) remains clear.
- Street width (F.O.C. to F.O.C.) = 24 feet
- Required clear lane = 24 feet/2 = 12 feet
- Therefore: Street flow in each gutter < (22'-11')/2 = 6 feet
Collector with open ditches
—
—
—
Arterial with side path
0.5
Spread of water flowing in gutter shall be limited so that half of roadway width (F.O.C. to F.O.C.) remains clear.
- Street width (F.O.C. to F.O.C.) = 36 feet
- Required clear lane = 36 feet/2 = 18 feet
- Therefore: Street flow in each gutter < (36'-18')/2 = 9 feet
Arterial Boulevard
0.5
Spread of water flowing in gutter shall be limited so that half of roadway width (F.O.C. to F.O.C.) remains clear.
- Street width (F.O.C. to F.O.C.) = 12 in feet in each direction
- Required clear lane = 12 feet/2 = 6 feet
- Therefore: Street flow in each gutter < (12'-6')/2 = 6 feet
NOTES:
Clear roadway width shall be centered within 4 feet of the roadway center line.
F.O.C. = Front of curb.
H. 
Detention pond requirements. The following requirements shall be met for detention facilities:
(1) 
An overflow spillway for the detention facility shall be required and must permit the passage of the runoff from the 100-year event if the primary outlet becomes clogged or for storm events larger than the 100-year event.
(2) 
The elevation of the top of the embankment shall be a minimum of one foot above the 100-year event.
(3) 
Finished floor elevations of adjacent habitable structures shall be a minimum of two feet above the 100-year water surface elevation of the detention facility.
(4) 
Detention facilities with a permanent water pool depth greater than one foot shall provide a ten-foot-wide safety bench with a 10:1 (H:V) slope just below the normal water surface elevation or provide a forty-eight-inch tall wrought-iron style fence or approved equal.
(5) 
Dry detention basins shall drain within 24 to 48 hours
(6) 
Maximum side slopes of all detention facilities shall be 3:1 (H:V), and side slopes of 5:1 are preferred.
(7) 
The pond bottom shall have a minimum 1.00% slope for dry detention basins.
(8) 
A five-foot-wide concrete low-flow channel shall be provided for dry detention basins.
(9) 
The minimum length to width of the detention facility ratio shall be 2:1.
(10) 
Dry detention basins must be solid sodded up to the top of bank. Wet retention basins shall be sodded from the top of bank to the normal water surface elevation and vegetated from the normal water surface elevation to the bottom of the pond. Alternative vegetative plantings may be allowed with approval from the City.
(11) 
All detention basins shall be a maximum of eight feet in depth from the top of bank to the bottom of the pond.
I. 
Open channel flow requirements. The following requirements shall be met for open flow channels:
Table 7
Grass-Lined Open Channel Design Criteria
Design Parameter
Requirement
Maximum velocity
< 6 fps for 100-year design
Manning's n: used to check channel capacity (flow depth)
0.040
Manning's n: used to check maximum velocity (channel stability)
0.030
Froude number
< 0.8
Longitudinal channel slope
> 0.75%
> 1.00% if no trickle channel is present
Maximum channel slope controlled by maximum channel velocity
Side slopes (maximum)
3H:1V
Channel bottom width (trapezoidal)
> 5 feet
Trickle channel (if any) sized for
2.0% of 100-year design peak flow for fully developed watershed
Trickle channel (if any) bottom width
> 5 feet
Center-line curve radius (feet) (subcritical flow)
> 2 times the top width of the 100-year design storm
Center-line curve radius (supercritical flow)
Supercritical flow not allowed
Channel freeboard
> 1 foot for 100-year design
Table 8
Concrete-Lined Open Channel Design Criteria
Design Parameter
Requirement
Maximum velocity
< 18-fps for 100-year design
Manning's n: used to check channel capacity (flow depth) 0.040
0.011
Manning's n: used to check maximum velocity (channel stability)
0.013
Froude number
< 0.7 and > 1.4 under both Manning's n
Longitudinal channel slope
< 1.00%
Side slopes (maximum)
1.5H:1V (unless structurally designed for steeper slope)
Channel bottom width
> 5 feet
Center-line curve radius (feet) (subcritical flow)
> 2 times the top width of the 100-year design storm
Center-line curve radius (supercritical flow)
No curvature permitted
Channel freeboard
> 1 foot for 100-year design
J. 
Storm sewer requirements.
(1) 
Design storm accommodation. Closed storm sewers for all conditions shall be designed to accommodate the ten-year design storm, based on the stormwater runoff collected and conveyed by the storm sewer system. Accommodating the design storm means the storm sewer shall be sized to convey collected runoff without surcharging using approved drainage design practices. All storm sewer shall be designed so that the hydraulic gradient is two feet below the ground surface (gutter line) for the entire length of the storm sewer run. The storm sewer shall also be designed so that it conveys at a maximum 80% full flow capacity during the ten-year design storm. Furthermore, all storm sewer must be able to manage the 100-year design storm runoff so that it is conveyed within the right-of-way or a drainage easement at all times and adjacent properties are protected from damage.
(2) 
Sizing. Industry standard pipe sizes shall be used for all storm sewer piping within the system with no pipe being less than 18 inches in diameter, unless a smaller pipe is requested and approved by the Lincoln Water Department prior to installation. Pipe sizes generally increase in size moving downstream since the drainage area and corresponding stormwater flows increase. Do not discharge the contents of a larger pipe into a smaller one, even when the capacity of a smaller downstream pipe has sufficient capacity to handle the flow due to a steeper slope. All pipe sizes shall be reviewed and approved by the Lincoln Water Department prior to installation.
(3) 
Material.
(a) 
Reinforced concrete pipe.
1. 
Reinforced concrete pipe (RCP) or reinforced concrete box culverts (RCB) shall be used in all right-of-way areas and under all traffic areas (including parking lots, driveways, etc.). All storm sewer pipe having a diameter or hydraulically equivalent pipe size diameter of 36 inches or greater must be RCP. RCP ASTM Class III shall be used in all areas unless otherwise required due to fill heights. Reinforced concrete pipe and reinforced concrete box culvert materials and installation shall meet the requirements of the latest edition of the ARDOT Standard Specifications, Sections 606 and 607, including bedding and backfill requirements. All end treatments shall have a flared end section or concrete headwall.
2. 
RCP shall conform to:
i. 
Circular pipe: AASHTO M170/ASTM C76.
ii. 
Arch-shaped pipe: AASHTO M206/ASTM C506.
iii. 
Elliptical pipe: AASHTO M207/ASTM C507.
(b) 
Corrugated metal pipe (CMP) [including smooth lined (SLCMP)] can only be used in areas outside of the street right-of-way but shall not be used under traffic areas. CMP shall have a minimum cover of two feet. CMP shall conform to the following:
1. 
Galvanized steel: AASHTO M218/ASTM A929; AASHTO M36/ASTM A760 and AASHTO Section 12/ASTM A796.
2. 
Aluminized steel Type 2: AASHTO M274/ASTM A929; AASHTO M36/ASTM A760 and AASHTO Section 12/ASTM A796.
3. 
Aluminum: AASHTO M197/ASTM B744; AASHTO M196/ASTM B745 and AASHTO Section 12/ASTM B790.
(c) 
High-density polyethylene pipe (HDPE) can only be used in situations where it is outside of the right-of-way or City drainage easement with the exception of a driveway culvert unless approved otherwise in writing by the City. HDPE can be used under driveways where the pipe conveys the flow of a roadside ditch and must be approved by the City prior to its use. HDPE shall be dual-walled with a smooth interior, corrosion and abrasion resistant, and soil tight. HDPE shall have a minimum cover of two feet and conform to AASHTO M 294 and ASTM F2306. All pipe shall be installed per manufacturer's specifications. The minimum cover of two feet may be reduced as necessary per written approval by the City.
(d) 
Reinforced concrete box (RCB), also includes three-sided boxes for these purposes, shall be structurally designed to accommodate earth and live load to be imposed upon the structure. Refer to the ARDOT's Reinforced Concrete Box Culvert Standard Drawings.
(e) 
When installed within the public right-of-way, all structures shall be capable of withstanding minimum HL-93 loading.
(4) 
Manning's roughness coefficients.
Table 9
Manning's Roughness Coefficients, n for Storm Drains
Materials of Construction
Design Manning Coefficient (n)
Reinforced concrete pipe (and reinforced concrete box)
0.013
Corrugated metal pipe
Plain or coated
0.024
Paved invert
0.020
Smooth lined
0.012
Corrugated polyethylene pipe
Plain
0.021
Smooth lined
0.012
Polyvinyl chloridge (PVC)
0.010
(5) 
Minimum grades. Storm sewer piping shall operate with flow velocities sufficient to prevent excessive deposition of solid material; otherwise, clogging can result. Storm drains shall be designed to have a minimum flow velocity of 3.0 feet per second when flowing under its ten-year design storm capacity. This velocity is accepted as producing scour potential when a storm sewer is flowing at its ten-year design storm capacity so that any deposition of solid material within the storm sewer will be cleaned out during the ten-year design storm. Grades for closed storm sewers and open paved channels shall be designed so that the velocity shall be no less than 3.0 feet per second for the ten-year design storm capacity nor exceed 12 feet per second for any design storm. The minimum slope for standard construction procedures shall be 0.40%. Any variance must be approved by the Planning Commission.
(6) 
Culvert design.
Table 10
Design storm frequencies and minimum freeboard
Description
Design Storm Frequency
Minimum Freeboard
(feet)
Trails
2
1
Local street
10
1
Collector
25
1
Minor arterial and major arterial
50
1
Bridges (local and collector roadways)
50
11
Bridges (arterial and critical service access roadways/drives)
100
11
NOTE:
1
From low chord/low steel.
A. 
Streets and alleys. It shall be the duty of every owner or occupant of any lot premises in the City along which any street or alleys runs, to keep said street or alley from the middle line thereof to the side next to him, free from all manner and kind of filth, garbage, trash, debris or decaying animal and vegetable substance of every kind.
B. 
Gutters or ditches. No person shall allow any filth or obstruction of any kind to accumulate in the gutter or ditch in front of his premises, and all owners or occupants of property are required to keep the gutter or ditch in front of their premises clean, open and free from trash, tall grass, and weeds and all obstructions to the easy and rapid flow of water.
(1) 
Exemptions from this requirement may be requested. The City Council shall vote on requested exemptions. Exemptions shall be based on existing conditions that make the area not reasonably feasible for a property owner or occupant to maintain, some of which could include, but are not limited to, the following:
(a) 
Presence of a major drainage pipe 30 inches or larger.
(b) 
Presence of a weir.
(c) 
Steep side slope in excess of two feet to one foot.
(d) 
Hydrology of ditch (water standing for more multiple days after a rain).
(e) 
Substantial sedimentation that requires equipment for proper cleanout.
(2) 
It shall be the responsibility of the owner or occupant to submit a written request for an exemption that describes the conditions which limit their ability to maintain the gutters or ditches in front of the premises within the City right-of-way.
C. 
Systems within the public right-of-way. Stormwater management systems located within the public right-of-way may be maintained by the City.
D. 
Systems on privately held land.
(1) 
The owner of the property on which stormwater systems and structures have been installed shall agree to maintain them in good condition and promptly repair and restore all grade surfaces, walls, drains, dams and structures, vegetation, erosion and sedimentation controls, and other protective devices. Such agreement shall be provided and approved prior to the granting of final plat approval (or certificate of occupancy in the case of a site plan). The owner of the property shall also provide a plan and such assurances as required so that the stormwater systems and structures will be maintained and repaired as needed in the future to assure the continuation of appropriate stormwater management for the development.
(2) 
Post-construction compliance. Upon completion of permitted construction activity on any site subject to the requirements of this article, the property owner and subsequent property owners will be responsible for continued compliance with the requirements of this article in the course of maintenance, reconstruction, or any other construction activity on the site.
(3) 
Easement required. All stormwater drainage and management systems on private land shall be placed entirely within a drainage easement encompassing all components of the system. Such easement will provide for a right-of-entry for inspection purposes. Such inspection will be conducted at reasonable times and in a reasonable manner.