r.cn(1) 	       Grass User's Manual		  r.cn(1)



NNAAMMEE
       rr..ccnn - Generates a SCS curve number map layer

       _(_G_R_A_S_S _R_a_s_t_e_r _P_r_o_g_r_a_m_)



SSYYNNOOPPSSIISS
       rr..ccnn

       rr..ccnn   ssgg==hy_soil_group	 lluu=landuse_map   pprr==practice_map
       hhcc==hy_condition_map ccnn==cn_map aammcc==AMC_number

DDEESSCCRRIIPPTTIIOONN
       _r_._c_n is a command-line interface for generating an SCS  CN
       (Curve Number) map.  The command format is:


       _r_._c_n    _s_g_=_h_y_s_o_i_l_g_r_o_u_p	  _l_u_=_l_a_n_d_u_s_e_m_a_p    _p_r_=_p_r_a_c_t_i_c_e_m_a_p
       _h_c_=_h_y_c_o_n_d_i_t_i_o_n_m_a_p _c_n_=_c_n_m_a_p _a_m_c_=_A_M_C_n_u_m_b_e_r

   PPaarraammeetteerrss::
       ssgg==mmaapp Hydrologic soil group map name

       lluu==mmaapp Landuse map name

       pprr==mmaapp Practice or management map name

       hhcc==mmaapp Hydrologic condition map name

       ccnn==mmaapp Output CN map name

       aammcc==nnuummbbeerr
	      Equivalent AMC condition number for the CN output

       The command-line ordering can be in any form but  all  key
       words must be there to run the program.

EEXXAAMMPPLLEE
       _r_._c_n  _s_g_=_h_y_._s_o_i_l_._g_r_o_u_p  _l_u_=_l_a_n_d_u_s_e _h_c_=_h_y_._c_o_n_d _p_r_=_v_e_g_._c_o_v_e_r
       _c_n_=_c_n_n_a_m_e _a_m_c_=_2
       will create a CN map cnname for equivalent  AMC	condition
       II



AATTTTEENNTTIIOONN
       _r_._c_n  uses information from the four map layers by reading
       the cell layer and its category files. So it is	important
       to  update  the	category  files (text attributes) for all
       four layers and it expects the categories of the map layer
       exactly as shown below:


       For  the hhyyddrroollooggiicc ssooiill ggrroouupp map the text categories may
       be either "A", "B", "C" or "D".	You  will  reclassify  an
       existing soil type map using rr..rreeccllaassss or vv..rreeccllaassss.


       For  the  llaanndduussee  mmaapp  layer  the  text categories may be
       either "fallow", "row crops", "small grain", "close-seeded
       legumes", "rotation meadow", "pasture", "range", "meadow",
       "woods", "farmsteads", "roads (dirt)", "hard  surface"  or
       "water".


       For  the  pprraaccttiiccee  or management map layer the categories
       may be either "straight row",  "contoured"  or  "contoured
       and terraced".

	 For the hhyyddrroollooggiiccaall ccoonnddiittiioonn map the categories may be
       "poor", "fair" or "good". The rating (good, fair, poor) is
       based on a combination of factors that affect infiltration
       and runoff, which includes:

		     density and canopy of vegetated areas

		     amount of year-round ground cover

		     amount of grass or close-seeded  legumes  in
		     rotations

		     percent of residue cover on the land surface
		     (good is more than 20%)

		     degree of surface roughness


       AMC is the antecedent moisture condition. AMC I: dry,  AMC
       II: normal, AMC III (wet). Specify this number during mod-
       ule run.


       The category text labels can  be  applied  to  above  maps
       using rr..ssuuppppoorrtt ("Edit category file").


       If  the combination of the four layers categories does not
       exist in the SCS CN table, an error message is printed and
       the program quits.



NNOOTTEE
       The  _r_._c_n  program is sensitive to the current window set-
       ting.  Thus the program can be used to generate a  CN  map
       of  any	sub-area within the full map layer. Also, _r_._c_n is
       sensitive to any mask in effect.



RREEFFEERREENNCCEE
       SCS Curve number method: TR-55, Urban Hydrology for  Small
       Watersheds

SSEEEE AALLSSOO
       _r_._w_e_i_g_h_t_e_d_._c_n _r_._s_u_p_p_o_r_t _r_._r_e_c_l_a_s_s _v_._r_e_c_l_a_s_s



AAUUTTHHOORRSS
       Raghavan  Srinivasan and Dr. Bernie A. Engel, Agricultural
       Engineering Department, Purdue University

       Extensions by Markus Neteler, University of Hannover, Ger-
       many (fixes for AGNPS 5)

       _L_a_s_t _c_h_a_n_g_e_d_: _$_D_a_t_e_: _2_0_0_2_/_0_3_/_0_1 _0_0_:_0_8_:_3_1 _$



