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_condi-
       tion_map ccnn==cn_map aammcc==AMC_number

DDEESSCCRRIIPPTTIIOONN
       _r_._c_n is a command-line interface for generating an SCS CN  (Curve  Num-
       ber) 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  cate-
       gories 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  combina-
       tion 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 module 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 setting.  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,  Germany	(fixes
       for AGNPS 5)

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



GRASS 5.0							       r.cn(1)
