KUEAL ENGINEERING. 189 



to care for the run-off from a rainfall of 4 in. in 24 hours, A formula 

 suggested by one of the authors for computing the run-off depth to be ex- 

 pected from any simple drainage area is as follows : 



in which D= maximum rate of run-off, in inches per 24 hours, to be ex- 

 pected from the rainfall P; C = a coefficient depending solely upon the physi- 

 cal character of the soil, and determined by experiment ; M= the ratio of total 

 run-off to total rainfall for the precipitation P, varying with evaporation, deep 

 percolation, lateral seepage from the drainage channels," and duration of flood ; 

 P=the depth of rainfall in inches in 24 hours (4 in. for Jefferson County) ; F= 

 the average slope of the ground surface of the drainage area, in feet per mile; 

 L= the mean length of the drainage area in miles; and B= one-half the mean 

 width of the drainage area in miles. For drainage areas that contain storage 

 reservoirs, a special calculation must be made to eliminate the effect of the 

 reservoirs. Where the main watercourse is formed by the junction of two or 

 more large tributaries, the foruiula is to be applied to each tributary separately, 

 and the proper value of the run-off depth for the entire area will be the 

 weighted mean of the values for the parts. . . . 



" The general plan proposed for the drainage of that part of Jefferson County 

 which can be wholly or partially drained by gravity consists in (1) dividing 

 that part into its natural drainage units, (2) straightening and enlarging all 

 the present water courses that will become the main outlets or arteries for a 

 complete drainage system, and (3) constructing systems of parallel ditches, 

 spaced one-half mile apart and running generally with the greatest slope of 

 the land, reaching to the boundaries of each district. The plan proposed for 

 the remainder of the county consists in (1) dividing it into convenient pump- 

 ing districts, (2) straightening and deepening certain water courses and con- 

 structing the proposed Intercoastal Canal, all of which will serve as outlets 

 for the pump discharges, (.3) building levees to prevent the overflow of those 

 districts by tides, backwater from the river, or run-off from higher lauds, (4) 

 constructing systems of parallel ditches spaced 1 mile apart and reaching to all 

 parts of each district, and (5) erecting pumping plants to lift the water from 

 such inclosures over the protection levees." 



The proposed plan of drainage includes thirty-two drainage districts and 

 water areas and areas outside of the districts covering 17,590 acres, all areas 

 totaling 611,900 acres of w^hich 530.670 acres will be benefited. The plan makes 

 necessary 1.630.3 miles of ditches and the total cost is estimated at $5,598,249 

 or $10.55 per acre. 



Bead building in swamps, E. IvRiJGER {Mitt. Vet: Ford. Moorkultur Deut. 

 Reiche, 32 (1914), No. 18, pp. 353-557).— Problems involved in the construction 

 of roads in swamp land under different conditions of drainage are discussed. 



Machinery for construction and maintenance: State, municipal, contrac- 

 tors, traction haulag'e of stone, care of machinery; instructions to engineer 

 and operator, T. R. Agg {Oood Roads, n. ser., 9 {1915), No. 1, pp. 21-24, figs. 

 2). — Principles applicable to the selection, operation, and maintenance of road- 

 building machinery are discussed. 



Motor-vehicle registrations and revenues, 1914 (U. S. Dept. Agr., Office 

 Sec. Circ. 49 {1915), p. i).— This report, prepared by the Division of Road 

 Economics of the Office of Public Roads of this Department, gives data for each 

 State with reference to the 1,666,984 automobiles, 44.355 motor trucks, 152,945 

 motor cycles, and 1,812 cars for hire, licensed in 1914, the number of operators' 



