When any earth, gravel, or other excavated material is caused to
flow, roll, or wash upon any street, the permittee shall cause removal
of same from the street within four hours after deposit to permit
safe flow of traffic. In the event the earth, gravel, or other excavated
material so deposited is not removed as specified, the Manager shall
cause such removal and the cost incurred shall be paid by the permittee
or deducted from his deposit.