Section 628 — Temporary Stream Diversions

Description

628.01This work consists of constructing, maintaining, and removing temporary stream diversions.

Material

628.02Conform to the following Subsections: Floating turbidity curtains 713.21 Gravel bags 713.13 Plastic lining 713.22 Rock for riprap 705.02 Sandbags 713.14 Sediment filter bags 713.19 Temporary culvert pipe 713.15

Construction Requirements

628.03Submittals. At least 14 days before starting stream diversion work, submit the following according to Subsection 104.06:

(a)Drawings and written narrative showing the type, size, location, elevation, and method of installation and remova l for the stream diversion, and means of access to waterways;

(b)A Fish and Aquatic Life Removal and Passage Plan. Include applicable Federal, state, and local permits and approvals;

(c)Sequence and schedule for the following:

(1)Installing and removing the diversi on;

(2)Removal of water from the work area;

(3)Accessing the waterways; and

(4)Fish and aquatic life removal from the work area.

(d)Best management practices used to ensure minimization of erosion and turbidity;

(e)Description of all construction stages;

(f)A list of on- site backup materials and equipment for emergency use; and

(g)Capacity calculations and hydraulic profile in an approved hydraulic modeling software.

628.04General. Provide a stream diversion system for expected flow during in -water work activities that accommodates at least a 2 -year peak flood event. Additional flow capacity may be required when in -water work activities occur during higher flow periods. Divert sufficient flow to sustain fish and aquatic life downstream. Do not constrict flow such that fluctuations in water depth, flow volume, and velocity cause erosion upstream or downstream of the project.

628.05Diverting Stream Flow. Use materials that are non -erosive for the expected flows. Maintain and control water flow downstream of the isolated work area for the duration of the diversion. Inspect and clean diversions of debris or sediment accumulation daily or according to an approved schedule. If required, install floating turbidity curtains within a body of water to minimize the migrat ion of sediment laden water out of the construction area. Divert the stream using one of the following methods and according to Section 107 :

(a)In-stream diversion. Place diversion berm, working from upstream end to downstream end. Maintain at least half -width channel flow. Minimize disturbance of channel bed. Minor quantities of in-stream material can be moved to help seal and secure diversion structures.

(b)Diversion channel. Excavate, stabilize, maintain, and operate the stream diversion channel to carry the diverted stream flow. Stockpile excavated materials in areas outside of the floodplain. Excavate the diversion channel with barriers installed at both ends of the diversion channel so stream flow does not prematurely enter the diversion channel. Line the entire length and width of the diversion channel with plastic liner or riprap according to Section 251. If plastic liner does not span the channel from bank to bank, place seams perpendicula r to the flow and place upstream sections overlapping at least 18 inches of the downstream section. Lay plastic liner flat on the channel in direct contact with the soil without any void spaces. Remove sharp objects to avoid puncturing the plastic liner. E nsure that the liner is secured at the upstream end of the channel and along the channel before removing barriers and diverting stream flow.

(c)Temporary culvert pipe diversion. Size and locate culvert pipe to minimize potential erosion. Stabilize the upstrea m and downstream ends of the culvert pipe to minimize erosion. Install the culvert pipe according to Section 602, and build the upstream flow barrier, followed by the downstream flow barrier.

(d)Bypass pumping diversion. Insta ll the upstream barrier first, followed by the downstream barrier. Suspend the intake above the channel bottom to prevent sediment from entering the intake. Place a mesh screen over the intake with a minimum mesh size of 3/32 inch. Enclose the intake with a secondary screen box 3 feet on each side if velocities at the intake are greater than 0.4 feet per second. Stabilize the discharge point at the downstream end to avoid erosion. Have spare pumps on site in the event of pump failures or higher than expected flow rates. Place the pump on firm ground with secondary containment measures. Remove water from the isolated work area as necessary to perform the work. Dispose of water according to Federal, state, and local rules and regulations. Do not discharge sedi ment laden water directly or indirectly to wetlands or waters. Pump water from the isolated work area to a temporary storage and treatment site or into upland areas and allow water to infiltrate. Control erosion at the discharge point.

628.06Removal of Stream Diversions. Upon completion of in- water work activities, restore isolated work area to match original or planned contours. Slowly restore stream flow to prevent loss of surface water downstream. Ensure isolated work area is stabilized and streambed material is washed down to remove dirt and fine sediment before stream flow is restored to prevent sudden releases of suspended sediment. Maintain sufficient stream flow downstream of the project to prevent stranding of aquatic life. Remove temporary flow barriers and diversion structures. Restore existing stream bank and floodplain topography, including restoring areas used for stream diversion to match original or planned contours.

628.07Acceptance. Material for stream diversions will be evaluated under Subsections 106.02 and 106.03. Construction, maintenance, and removal of stream diversions will be evaluated under Subsections 106.02 and 106.04. Culvert pipe will be evaluated under Section 602. Riprap will be evaluated under Section 251.

Measurement

628.08Measure the Section 628 pay items listed in the bid schedule according to Subsection 109.02 .

Payment

628.09The accepted quantities will be paid at the contract price per unit of measurement for the Section 628 pay items listed in the bid schedule. Payment will be full compensation for the work prescribed in this Section. See Subsection 109.05 . Progress payments for temporary stream diversions by the lump sum will be paid as follows:

(a)50 percent of the pay item amount will be paid after installation.

(b)The remaining portion of the pay item amount will be paid after the temporary stream diversions are removed from the project.