SEWAGE OUTFALLS AND DISCHARGE 315 



dry weather flow of a sewage for 24 hours would admit of six 

 times the dry-weather flow passing through such tank by 

 reducing the time of stay from 24 hours to 4 hours. The rate 

 of flow under such conditions would still be so slow as to ensure 

 the retention in the tank of nearly all the suspended solids, and 

 these would therefore accumulate during stormy weather to be 



Storm Overflow 



(Immediate) 



Storm Overflow 



(Deferred) 





Fig. 58. — Storm Overflows at Barrhead. 



digested by the tank at leisure during the dry-weather periods. 

 A curious anomaly arises out of these considerations. If the 

 time of sojourn in the tank is reduced owing to the rate of flow 

 through the tank being increased, the liquid products of hydro- 

 lysis usually contributed to the effluent from the stay in the 

 tank will not exist in the effluent water to the same extent. In 

 other words, the effluent from such a tank during a storm will 

 be purer than from the tank in dry weather proportionately to 

 the rate of flow, even after due allowance has been made for 

 dilution, provided only the rate be not so high as to bring 



