R655-11-6E. Internal Drainage

A. All underdrains and collection pipes shall be constructed using non-corrodible materials capable of withstanding the anticipated loads.

B. Underdrains and collection pipes should be designed to conduct flows several times larger than anticipated. All pipes within the dam which are not easily accessible shall have a minimum diameter of six inches.

C. All internal drain pipes should be enveloped with free draining material, meeting filter requirements with adjacent zones.

D. Where multiple pipes are used to conduct drainage from internal portions of the dam, they should be carried to the downstream toe or gallery separately without intervening connections or manifold systems. If the drain pipes are connected at their termination points, manholes should be provided to facilitate observation and measurement of the separate drain lines.

E. All underdrains and collection pipes should have provisions for measuring discharges in manholes or at their discharge points. If the anticipated discharge is in excess of 10 gallons per minute (gpm), a weir or other suitable measuring device should be provided. If the anticipated flows are less than 10 gpm, provisions should be made so the water can be discharged freely into a vessel 1.5 feet high and one foot in diameter.

F. All exposed underdrain and collection pipes shall have an appropriate rodent screen attached.

G. All underdrains and collection pipes shall be cleaned out and inspected by camera prior to the first filling of the reservoir.

H. All seepage collection systems must include a collection pipe to discharge flows.

I. All internal drains must have a sufficient cover of impermeable material to eliminate the collection of surface waters.