Encyclopedia of Environmental Science and Engineering, Volume I and II

URBAN RUNOFF 1189

Self-cleaning Storage/Sedimentation Basin In Zurich,

Switzerland, an in-line sedimentation storage tank was

designed to prevent solids from shoaling after a storm

and to provide for solids transport to the interceptor. The

floor of the tank contains a continuous dry-weather chan-

nel (which is an extension of the tank’s combined sewer

inlet) that meanders from side to side (see Figure 9) through

the tank. This channelized floor arrangement allows for

complete sediment transport to the interceptor both during

dry weather and upon drawdown after a storm event. The

dry-weather flow comes through the meandering bottom

channel. During wet-weather flows, the water level in the

tank rises above the channel. If the storm intensity is low

enough, there is complete capture, and if the storm intensity

continues to rise, an overflow occurs through a weir at the

tail end of the tank. A scum baffle prevents entrained solids

from overflowing. This arrangement allows for sedimenta-

tion to take place during a tank overflow condition and, at

the same time, for transport of solids that settle by way of

the bottom channel.

TO RIVER

TO TREATMENT

PLANT

STORMWATER

OVERFLOW

CHANNEL

DWF CHANNEL

SLUICE

GATE

INLET

TO BYPASS

PLAN VIEW WITH

SLUICE GATE DOWN

BY-PASS PIPE

CSO

CSO TRUNK

INLET

STORMWATER

OVERFLOW

CHANNEL

DRY,WEATHER FLOW

CHANNEL

TO RIVER

TO T.P.

OVERFLOW WEIR

SCUM BAFFLE

PLAN VIEW

DETAIL A

DETAIL A

SECTION A–A, ELEVATION VIEW

FIGURE 9 Self-cleaning storage-sedimentation basin.

T A B L E 9

Summary of in-pipe storage costs (ENR 
 5,000)

Location

Storage Capacity

(Mgal)

Drainage Area

(acre) Capital Cost ($)

Storage Cost

($/gal)

Cost per Acre

($/acre)

Annual O&M

Cost ($/yr)

Seattle, WA Control &

Monitoring System

— — 8,748,550 — — 182,500

Automated Regulator

Stations

— — 9,747,970 — — 550,410

Total 17.8 13,120 18,496,520 1.06 1,411 732,910

Minneapolis—

St. Paul, MN

NA 64,000 7,531,870 — 117 —

Detroit, MI 140 89,000 7,024,910 0.6 78 —

NA 
 Not available.

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