Page 9 - Section4.1.1-SWPPPCutSheet-FiltrexxSedimentControl

332 | Filtrexx ® Low Impact Design Manual | Version 8.0

7. Standard diameter size of Check dams for normal protection is12 in (300mm). Inhighfow ditches/channels, the Engineer may specify larger Check dams of 18 in (450mm) or 24 in (600mm) diameter.

8. Check dams may be stacked on top of each other, if additional height is required.

9. 8 in (200mm) diameter Check dams may be placed closer together to act as ‘speed bumps’ to slow fow velocity and reduce ditch/channel bed erosion.

10. If Check dams are specifed as a “Λ” construction design, the angle of the Check dam must be confgured to a 90 degree angle with the apex of the device in the center of the ditch/channel bed with the open end facing down-channel. Ends of Check dams shall extend to the bed and bank interface or to the maximum fow line of the ditch/channel. Stakes shall be used to stabilize the ends of the Check dam.

11. Stakes shall be installed through the middle of the Check dam on 5 ft (1.5m) centers, using 2 in (50mm) by 2 in (50mm) by 3 ft (1m) wooden stakes.

1 2. Staking depth for sand and silt loam soils shall be 12 in (300mm), and 8 in (200mm) for clay soils.

13. Vegetated Check dams may be seeded at the time of manufacture and installation to create a contained ‘green or living bio-flter/vegetated flter’. These may be left intact once construction phase in complete. The appropriate seed mix shall be specifed by the Engineer.

14. Check dams may be installed on top of rolled erosion control blankets and turf reinforcement mats.

INSPECTION and MAINTENANCE

Routine inspection should be conducted within 24 hrs of a runoff event or as designated by the regulating authority. Check dams should be regularly inspected to make sure they maintain their shape and are producing adequate hydraulic fow-through, ditch/channel erosion control, and sediment removal. If ponding becomes excessive, additional Check dams or sediment removal may be required. Sediment accumulation should be removed once it reaches ½ the height of the check dam. Alternatively, another Check dam may be installed slightly upslope, on top of the existing one. This process is not considered a soil disturbing activity. Storm debris accumulation behind Check dams should never be higher than the sides of the check dam. Storm runoff overfow

is acceptable during large events. Check dams shall be inspected until drainage area above and around receiving ditch/channel has been permanently stabilized and construction activity has ceased.

1. The Contractor shall maintain the Check dams in a functional condition at all times and it shall be routinely inspected.

2. If the Check dam has been damaged, it shall be repaired, or replaced if beyond repair.

3. The Contractor shall remove sediment at the base of the upslope side of the Check dam when accumulation has reached 1/2 of the effective height of the Check dam, or as directed by the Engineer. As an alternative, another Check dam may be installed adjacent and parallel to the upslope side of the original to increase sediment storage capacity. Check dam and sediment backup in center of the ditch/ channel shall remain lower than the sides.

4. If Check dam becomes clogged with debris and sediment, immediate removal of debris and sediment should be conducted to assure proper drainage and water fow through the ditch or channel. Storm runoff overfow of the Check dam is acceptable.

5. Check dams shall be maintained until disturbed area around the device has been permanently stabilized and construction activity has ceased.

6. The FilterMedia tm may be dispersed on site once disturbed area has permanently stabilized, construction activity ceased, or determined by the Engineer.

7. Permanent vegetated flter strips will be left intact.