Stormwater Manual - Pima County Flood Control District

Temporary or permanent seeding and mulch must be applied to the berm or ditch immediately
following its construction. Triple-seed areas below the flow line, and use erosion control
blankets or turf reinforcement mats as needed.
Maintenance
Bare and vegetated diversion channels shall be inspected regularly to check for points of
scour or bank failure; rubbish or channel obstruction; rodent holes, breaching, or settling of
the ridge; and excessive wear from pedestrian or construction traffic.
Damaged channels or ridges shall be repaired at the time damage is detected. Sediment
deposits shall be removed from diversion channels and adjoining vegetative filter strips
regularly.
Diversions shall be reseeded and fertilized as needed to establish vegetative cover.
11.4.11 Level Spreader
Level spreaders are storm flow outlet devices constructed at zero grade across the slope
whereby concentrated runoff may be discharged at non-erosive velocities onto undisturbed
areas stabilized by existing vegetation. A level spreader is illustrated in Figure 11-13.
Level spreaders dissipate storm flow energy at the outlet by converting storm runoff into sheet
flow and discharging it onto areas stabilized by existing vegetation without causing erosion.
Level spreaders are used at diversion outlets and other locations where sediment free storm
runoff is intercepted and diverted from graded areas onto undisturbed stabilized areas. The
practice applies only in those situations where the spreader can be constructed on undisturbed
soil and where the area directly below the level spreader is stabilized by existing vegetation.
The water must not be allowed to reconcentrate below the point of discharge.
Design Criteria
The length of the level spreader shall be based on the peak flow from the 100-year storm in
accordance with the following table
100-year Peak Flow (cfs)
Minimum Length (ft)
Up to 10 15
11 to 20 20
21 to 30 30
31 to 40 40
41 to 50 50
Construction Specifications
The minimum acceptable width shall be 6 feet. The depth of the level spreader as measured
from the lip shall be at least 6 inches and the depth shall be uniform across the entire length of
the measure.
STORMWATER MANUAL 11-29 August 29, 2011
LEXINGTON-FAYETTE CO., KY.