14-44.1 LAND GRADING METHODS General Land grading for drainage consists of shaping the land surface by cutting, filling, and smoothing to Ii continuous grade as shown in Figure 14-22.1. A continuous grade is necessary to assure uniform £lm", of runoff water over the land surface or along crop rows without ponding. Shaping land into a plane surface to provide uniform slopes in both a lateral and longitudinal direction normally is not essential but may be advantageous in sit~ations where: (1) grading of the site can be handled more efficiently; (2) economical and efficient operation of special planting and harvesting machinery is necessary for high value crops; (3) change in crop row direction is desired; and (4) surface irrigation is used. Detailed surveys, planning, and layout are necessary for land grading jobs. Emphasis in planning is given to filling depressions with soil av8.iJJ!QlILfromjmmedial" el y a dJDi.-nin~i4~----a-nd--metffid-s.~Whe"re--the-mactt"",e~-~------­ rial required for filling low places is excessive, or sufHcient soil is not available, random field ditches can be established and surfaces warped toward them. In areas with little or no land s lope, surface grades can be increased by grading bet,veen parallel field ditches, with the cuts made from the edge of one ditch and the fill placed with increasing depth toward the edge of the next upper ditch. Surface ridging similar to bedding can be es tablished also by sheWing and smoothing land surfaces and ditch spoil between a system of closely spaced and graded field ditches. The artifi­ cal ridge is created midway be~yeen ditches. Approxinmtelyparabolic convex surfaces are developed by shaping from the ditch shoulders to the ridge. Necessary crm'i'n heights and fill are obtained by an adjustment in spacing"between ditches, flattening ditch side slopes, and use of ditch spoil. Ditch spacing and crown heights should be obtained from the state drainage guide. Rm", lengths w.ill vary according to soil permeability and. grade. Row grades on nonplastic, permeable, and erodible soils should seldon exceed 1/2 percent, although on plastic and slowly permeable soils, grades may run as steep as 2 percent. Recommended grades and row lengths also should be obtained from the state drainage guide. Land grading for drainage is an intensive practice, the cost of which may be reduced by separating fields or portions of fields into areas having about the same slope and soil characteristics. These areas then provide a basis for selecting a proper field arrangement, which takes into account: (1) planned land use; (2) length of row or distance of ,,,,ater travel overland; (3) auxiliary drainage measures such as outlets and diversions; (4) access roads; (5) supplemental borrow; and (6) waste areas, if needed. To illustrate methods and procedures, a representative problem for the Northeast is shown in Figure 14-22.2 through Figure 14-22.6. The problem assumes a 13-acre hay and pasture field (ACIG) consisting of slowly permeable clay loam soil which generally is wet and produces only 14-44.2 lovl-yielding and poor-quality hay and pasture. Drainage improvement requires protection from upland flooding and seepage by means of a diversion (CEl), a lateral (BDFH) at the break in slope, and a disposal channel consisting of a Vlatenvay (KL) and a main (JK). The sloping field section (BCIH) has a good down field grade of over 3 percent and a cross slope grade bebveen 1 and 2 percent which will provide good furrow drainage 'Ivithout erosion ,vhen plowed. The flat section (ABHG) has several wet depressions. Grading and smoothing are necessary to develop a free draining surface toward the outlet. 1.5 I I Existing Surface .... --'~ 1.0 ..... - -- ..... -..- 1-- .--- 0.5 - ~ "-- Finished Surface on Continuous Grade/ 0.0 I I I I ~ 0 0 0 0 0 0 0 0 0 0 0 0 o 0 -~, + + 01- + ... + o • N fi') <;I' 10 1.0 LI. 5 L __ ~ __ _ I I I I I Figure 14-22.1 Surface graded for drainage Surveys Topographic surveys must be made to provide a basis for planning the surface grading and auxiliary drainage system. The intensity of surveys may range from a few scattered shots on land surfaces having a pronounced slope to a precise grid-type survey on slightly sloping to flat surfaces (1 percent or less). Bench marks and points of known horizontal position need to be located and mapped so that both vertical and horizontal control can be reestablished on the ground. Figure 14-22.2 illustrates a plat of essential survey data for improvement of the total field area (ACIG). In addition to topographic data, an adequate number of soil borings should be made to determine depth of topsoil so that depth of grading can be controlled, when necessary, to prevent exposing harmful amounts of subsoil. After the job has been planned, further staking of the sloping field -" area (BeIH) may not be necessary. However, grid stakes must be set for grading the flat field area (ABHG). Since stakes cannot be maintained for long in farm fields, staking and final design for surface grading 14-44.3 --------~-------------~ c SURVEY MAP 34.0 loo X A r ' 1 31.0 31.7 2 32,8 X X mX >; l( ·0 o \ ..J 30.8 31.3 31.5 32,3 )( X l( X 30.7 31,0 l( )( r\ "i' 30.6 c~31.0 31.3 3~:7 l 31.6 X X X U X 30.7 31.4 30.8 30.9 X X X )( G BM 30,80 30.8 . )( -X- J 2U MAIN 29.4 - Figure 14-22.2 Land grading and smoothing () < (} (/)-i c: o :::r~ 0- ..... Z :xl o o l' 0 o :;, <.oJ ~ n ... B ;1':' '"g. z A -< 0 () o 'T1 ... .. " 3.87 3.67 3.47 3.27 o :;, c o w 111 4.0 3.3 3.8 2.2 II) !.~I 20 = 4 x 5t! ;.." X X X X 0.. "0 ) ~r F .13 C .37 F .33 C 1.07 In (I) .. ..., ~1 "'''' :>' '" () c.n '" c: ,... o =1 4.02 3.82 3.62 3.42 3.22 ;1 ":> ::or­ '" '" 4.2 3.7 3.5 2.7 Z.4 (I) -I 24" 6 x 4H en X X X X X I ;1 ~rr-Cl' 0- F .18 C .12 C .12 C .72 C .82 .".. " I :!,I (.W 0 1 f I 1 ~ 4.17 3.97 3.77 3.57 3.:n ... 0 i;; 4.3 4.5 4.0 3.63 4.3 2.7 ~ )( tH.I-CD . 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FIRST TRIAL SINGLE PLANE OF BEST FIT (.W­ VJ o VJ -0 IJ) o (Jl r.o VJ (Jl CO Figure 14-22.3 Plane method for land grading and smoothing ) ) 0 < -i (J)-I c: 0 0 ::r 0 C" _.... 0 ...-.0 - 0 A B ('\ => I ...... -< 0 (") ~"Tl 5.42 3.72 3.52 3.32 0 => c: a 4.0 3.3 3.8 2.2 ... -e .." '0 x X X X a. I ? en tt> F .58 C .42 F .32 C 1.12 I l> ... a. •'" (') en [ Q. c: c: 0 I r I II> c ::0:- -I 4.07 5.87 3.67 3.47 3.27 ~ I Q. 3 I '" 4.2 3.7 1 I (1) 3.S 2.7 2.4 n en It l( l( X X J( I f => ! 0 F .13 C .17 C .17 C .77 C .87 (.N .., 0 I I C 1.01 (.N I CD co ox (.N. • ~ I !-"N -CO-(.N(J1--.JI-~l ~ 4.22 4.02 3.82 3.62 3.42 3.2 g o~ 00 .t>~o (J1 (J1 ~ 4.3 4.5 4.0 4.3 2.7 2.2 2.4 0 X Xl( 3.68 x X X X (')0 F .OB F.48 F .18 ~.6B C .72 C 1.0 C .62 != 0 -< I-' Centrold1 a. ...,. 0 I I II> I~ (it +-...,. 4.37 4.17 3.97 3.77 3.57 3.3 3.17 .