tion, the Red Cross, and others, to the regions to which they may be 

 required. 



3. Advise in the operation of flood control dams and reservoirs in order 

 to obtain the most advantageous use of the works and structures. 



The attention of the Flood Warning System is directed primarily to the more 

 heavily populated section of the Province, or an area of some 30,000 square 

 miles. 



A variety of weather forecasts is issued by the Meteorological Branch, and 

 is available to the Flood Warning System. A general forecast, covering a two- 

 day period, is issued at six-hourly intervals, and is generally adequate for 

 maintaining a normal river watch. Special warnings are issued whenever heav>' 

 rains of one inch or more are expected. These warnings indicate the amount, 

 location and time of the rain, along with the speed and direction of motion of 

 the storm. These warnings are issued up to 24 hours before the occurrence of 

 the rain. 



Weather forecasts and advisories are correlated by the hydrometeorologist 

 with current data on soil moisture and river flow conditions with stream flow 

 characteristics. 



An extensive program has been undertaken with the installation of recording 

 stream gauges on the rivers of Southern Ontario. As information from these 

 gauges becomes available, it is used to prepare graphs and other data necessary 

 to assess stream flow characteristics. All major storms and many minor ones 

 are analyzed in order to obtain as much detailed information as possible on 

 stream flow conditions. 



Detailed and up-to-date information on the prevailing river stage, flood 

 storage available in reservoirs and soil conditions, is on hand at all times for the 

 river forecaster. 



For forecasting purposes, soil conditions are translated into runoff rates 

 through calculation of the antecedent precipitation index. The method used is 

 similar to that developed by the United States Weather Bureau. 



Measurements of the depth of snow and its water content are taken over 

 the region at regular intervals throughout the winter. These are particularly 

 important in assessing the flood potential of the spring runoff or the development 

 of floods as a result of winter rains. 



From such data and calculations, the river forecaster in the Branch issues 

 weekly advisories to the Field Officers who are responsible for watershed manage- 

 ment in their particular region. These advisories indicate the amount of runoff 

 to be expected with varying amount of rainfall under the prevailing soil moisture 

 conditions. The extended period weather forecasts are also issued along with 

 these advisories. By this means the men in the field are kept advised of the 

 prevailing conditions as they affect their particular river, and are alerted to the 

 possibility of adverse weather conditions. They are expected to keep a watch 

 on short period forecasts as a supplement to the weekly advisories. 



Flood forecasts and activities during actual flood conditions are issued at 

 the discretion of the Hydrometeorologist whenever he feels they are warranted. 

 Once a river forecast has been issued, advisories are given on the development of 

 flood conditions until such time as a final message is issued indicating the end of 

 a flood alert. 



In order to obtain direct information of rainfall amounts and intensity which 

 may result in flooding, a network of special rainfall observers has been established 

 to assist the flood forecast system. These observers send a telephone call to the 

 river forecaster whenever they receive an inch or more of rain within 24 hours. 



34 



