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Command Area Survey

command area survey for irrigation projects




GOVERNMENT OF ODISHA DEPARTMENT OF WATER RESOURCES INDUCTION TRAINING PROGRAMME MODULE-IV (INVESTIGATION) (INVESTIGATION) COURSE CODE: INV-IV  Command Area Survey !"na#"$a%"on o& LS ' DS CIE! ENGINEER PP! ' INV 1 ODISA *U*ANES+AR 2 Command Area Survey Some technical terms as regards to water application are as follows: 1. Gro!Command Area "G.C.A#$  The total area including roads, villages etc. which can be economically irrigated from the project is called grosscommand area. n other words, it is the total area over which water of irrigation canals can !ow under gravity. "s a matter of fact, depending upon the available source, only a part of  the area can be irrigated. %. Cu&'ura(&e Command Area"C.C.A#$  That area over which cultivation is possible within project #.$."., is %nown as culturable commanded area. t is obtained by deducting uncultured area li%e ponds, barren land, forest, village etc., from the #.$.". ). Un!*ommand Area$ n the culturable command area, there may be some high level culturable areas, where the irrigation water cannot !ow under gravitational force from the canal. Such &eld areas are declared un-command areas and no water is allotted to them. Such areas may be irrigated by tube-wells or other methods of irrigation. +. Cu&'ura(&e Cu&',va'ed Area$  The area which is used for growing crops in the particular season. -. Cu&'ura(&e Un*u&',va'ed Area$ '  The area where irrigation is possible, but crops are not grown in a particular season. The area left for the crops of ne(t season is %nown as culturable uncultivated area. Ho Command Area Survey , *ondu*'ed $ommand area survey can be carried out on the village maps. "ppro(imate command area )ayacut area* can be calculated from the topo sheet and number of villages to be involved in the command area. $ontour survey can be carried out from spot level basis or grid plan method. Spot levels are ta%en on each plot of the village and smooth curves)contour* of 1.++mtr interval are drawn along the points of eual levels. Spot levels are ta%en on the corner points of the suare grid without referring to the plots of the village, which %nown as grid plan method of contouring. "fter drawing the contour lines the obligatory areas li%e hills, forest, human settlement, ponds, schools, roads, are deleted and the net area is termed as culturable command area)$$"*. " contour map is attached for reference. A&,/nmen' O0 Ma,n Cana&R,d/e 2,neVa&&ey 2,neC3a4  5oundaryD,'r,(u',on Sy'em Ma,n Cana&$  This is the canal which is directly ta%en o from a river or reservoir. t is usually of large sie and no direct irrigation is done from it to the &elds e(cept under special circumstances. t functions as a carrier of feed canal to branch and other canals. 5ran*3 Cana&$ / "s the command area of big canals is very large, it is not possible to supply water from one canal. 0or supplying the water to the total area the main canal is bifurcated into two or more canals, which are %nown as branch canals. ach branch canal is responsible to irrigate a particular area. The branch canals also do not supply water direct to the &elds, but serve as a feeder of the distributaries. ut in special circumstances outlets for irrigation purposes can be provided on high spots, which cannot be irrigated from the distributaries. D,'r,(u'ar,e$  These are channels which carry small discharge of +.3 to 4.+ $umecs. They draw their uantity of water from the branch canals. 5ost of the irrigation is done by distributaries, as they carry water to various places of the command area. M,nor$ Sometimes these are also %nown as minor distributaries. They draw their water from the distributaries. "s most area along the distributaries and branches is high and cannot be irrigated, therefore at such places a minor is run more or less parallel along the branch canal to irrigate these &elds. 6utlets are provided in the minors at various points for irrigation purpose. 5inors carry discharge from +.23 to +.3+ $umec. "bout 1+-13 outlets are provided in each minor. Wa'er Coure$  These are also %nown as &eld channels and are constructed and maintained by the farmers. These are small channels which draw 3 water from the minors through their outlets and carry it direct to the &elds for irrigation purposes. They may be lined or unlined. 7ow-a-days farmers are being stressed to ma%e the water courses lined to save the precious water from percolation loss. n special cases they can also draw water from branches and distributaries. Cana& A&,/nmen'$  These canals are constructed nearly parallel to the contour lines of the area. 8sually main canals are constructed along the contour lines for some length near the diversion head wor%. ranch canals and distributaries are also constructed as far as possible on the contour lines. The contours chosen for the alignment should include all the contours of the area to be irrigated. The contour canal irrigates the areas whose elevation is lower than the elevation of the canal, because water !ows under gravity from it to the &elds. f irrigation facilities are to be provided for the higher areas, lift irrigation canals are provided. R,d/e Cana&$  The canals constructed on the ridge or water shed line are %nown as ridge canals. These canals are usually ta%en o from the contour canal. "s this canal can irrigate &elds on its both the sides, its command area is more. These canals also do not meet with any cross drainage wor%s, therefore their construction cost is also low. 9hile doing the construction of these canals if the ridge ta%es sharp turn, the alignment of the canal should be made straight as far as possible, because it reduces the length of the canal and thereby construction cost. 5ost of the irrigation canals are ridge canal.  S,de S&o6e Cana&$  These canals are aligned appro(imately at right angles to the contour canals along the slope between the ridges and the valleys. 8sually these are parallel to the natural drainage of the area, therefore, no cross drainage wor%s are reuired in them.  These canals have steep bed slope, therefore, lining is done in them, otherwise heavy velocity will erode them. " number of main canal alignment are decided upon the area of the command and the location. f the command area are located on both sides of the dam;barrage two main canals are planed on both sides on the barrage ;dam at suitable location. #enerally the o-ta%ing point of the main canal is &(ed at 1.3+mtr below the 59< in case of barrage. " main canal alignment runs a contour line which decreases 1.++mtr in 3.++%m distance till the canal reaches a bigger 7alla or water body. The main canal &(es the boundary of the command area. =istribution system of the canal )distributary, minor, sub-minor* are decided to distribute the water to the entire command area through its canal 7etwor%. The distributory, minor and sub-minor generally follows ridge line of  the area in order to distribute water on both sides of the canal through its outlets. C3a4 5oundary In'rodu*',on  The cha% or outlet command is a basic unit for irrigation management in the command of 5inor, distributory or any other parent channel. Therefore, establishing layouts of the cha%s in the command of a given channel is the &rst step of the planning 4 process. 0or this purpose, the contour map of the command of  minor or distributory to the scale of 1:2+++)1:/+++ if command is very big* with contour interval of +.2 or +.' m should be adopted. Layout of chaks: 0ollowing factors are considered boundaries and total layout of cha%s. o o o o o for &naliing cha%  Topography )>idges, vallies, local depressions, high patches, etc.* 5a(imum permissible area which can be irrigated in pea% rotation by prescribed discharge in a given !ow period. 5a(imum length of &eld channel.  The number of farmers to be served. 6ther factor li%e village boundary, road;railway lines, etc. " map is attached showing the contour lines, canal alignment with distribution system and cha% boundary. Pre6ara',on o0 2S 7 DS. o0 Cana& The command area )$$"* of a minor or sub-minor is decided on the contour map drawn in suitable scale. The corresponding to the $$" discharge reuired in $umecs ?+.@43lps ; ha. is calculated with 1+A e(cess for &(ing the canal parameter li%e ed width , =epth of !ow, the ed level of the canal is &(ed with full supply level. $ontinuing in the same process the other minors @ are ;sub-minors are designed from the tail end of the canal towards head of the canal and the &nal discharge is &(ed at the head regulator of the canal. The = in mtr. 2.S OF 8RUSHNA CHANDRAPUR SU5!MINOR!1 FROM CH$ 99 TO :%+.9 AND DESIGN STATEMENT OF PAUNSIA DISTRI5UTOR; OFFTA8ING FROM RD %:%:9.9M OF 5ETNOTI 5RANCH CANA2 ARE ATTACHED FOR REFERENCE oo% >eference: 1. rrigation ngineering and Cydraulic Structures by Santosh Dumar #arg. 2. rrigation ngineering by #.S irdie E >amchandra =as. F 1+ 11 12 1' 1/ 13 1