Unified Development Ordinance, 32nd Supplement, July 2024

CHAPTER 9. ​NATURAL RESOURCE PROTECTION | Article 9.5. Watershed Protection Areas

Maximum Permissible Velocity* (F.P.S.)

Fine sand (noncolloidal) Sandy loam (noncolloidal) Silt loam (noncolloidal)

2.5 2.5 3.0 3.5 5.0 5.0 5.0 5.5 3.5 5.0 6.0 5.5 6.0

0.8 0.8 0.9 1.1 1.5 1.5 1.5 1.7 1.1 1.5 1.8 1.7 1.8

Group No.

Depth of Flow (feet)

Vegetation

Annuals:** Annual lespedeza (KOBE)

Ordinary firm loam

t1

2.5

Fine gravel

5

Stiff clay (very colloidal)

Sundangrass Small grain (rye, oats, barley): Ryegrass

u1

2.5

Graded, loam to cobbles (noncolloidal) Graded, silt to cobbles (colloidal)

*Do not use on channel slopes steeper than 10%, except for side slopes. **Annuals: use as temporary protection until permanent cover established. 3. General Velocity Standard Any area of a land-disturbing activity or receiving watercourses subject to stormwater runoff velocities in excess of those specified in Sec. 9.4.4.G.2. above from accelerated erosion by provision of an erosion-resistant lining of vegetation in accordance with Sec. 9.4.4.G.2.c. above provided, armored, paved or otherwise nonvegetative watercourse lining shall be provided anywhere the velocity in the receiving watercourse exceeds Sec. 9.4.4.G.2.c. and the prior development velocity by 10%. 4. Critical Soils When the following soils (as defined and described in the soil survey of Wake County North Carolina Soil Conservation Service, United States Department of Agricultural, November, 1970) which are especially vulnerable to erosion from stormwater discharge from land-disturbing activities, occur between a point of stormwater discharge and the next confluence of concentrated stormwater runoff, such areas, on- or off-site shall be protected from accelerated erosion by diverting the stormwater discharge from those soil surfaces. The application of this section may not prevent discharge of stormwater from a land-disturbing activity site. Diversion may include the provision of piped, paved or armored storm drainage facilities:

Alluvial silts (noncolloidal) Alluvial silts (colloidal) Course gravel (noncolloidal)

Cobbles and shingles Shales and hard pans

c. The velocity specified according to the following for a discharge point into a vegetated receiving watercourse.

Maximum Permissible Velocity* (F.P.S.)

Group No.

Depth of Flow (feet)

Vegetation

t1

4 6 3

1 Bermudagrass

u1

Tall fescue

t1

2

Reed canarygrass Kentucky bluegrass Grass and legumes, mixed Weeping lovegrass Lespedeza, sericea Red fescue, Red top

u1

6

t1

3

3

u1

4

t1

2.5 2.5

4

u1

a. Applying sandy loam, 10% to 15% slopes (ApP); b. Cecil sandy loam, 10% to 15% slopes (CeD); c. Cecil sandy loam, 15% to 45% slopes (CeF); d. Creedmore sandy loam, 10% to 20% slopes (CrE);

Supp. No. 32

9 – 48 Published July 2024

Part 10: Unified Development Ordinance City of Raleigh, North Carolina