%    
%	clc_znot
%	z0/Ks = f(R*)
%
%	given Ks, Ustr, and nu (all in same units) calculates z0.
%	assumes that all inputs are in consisten units. (cgs or SI).
%  Coded by Courtney Harris, originial code fit by Patricia Wiberg.
%       ckharris@vims.edu; pw3c @virginia.edu
%
	function [z0,z0_in]=clc_znot(Ks,Ustr,nu);

	rho = 1.0;		% water density.


%	calculate grain roughness
	Rst = Ks*Ustr/nu;		% roughness reynolds number

	lnRst = log(Rst);

	if (Rst<=3)			% Hyd Smooth Flow
	   z0_ks = 1/(9*Rst);
	elseif (Rst<=6)			% transitional flow
	   z0_ks = -0.00798*(lnRst^3) + 0.05428*(lnRst^2) - ...
		    0.12569*(lnRst)   + 0.1199;
	elseif (Rst<=35)
	   z0_ks = -0.00141*(lnRst^3) + 0.01543*(lnRst^2) - ...
		    0.04859*(lnRst)   + 0.0686;
	elseif (Rst<=200)
	   z0_ks =  0.00053*(lnRst^3) - 0.00930*(lnRst^2) + ...
		    0.05377*(lnRst)   - 0.0696;
	else				% Hyd Rough Flow
	   z0_ks = 1/30;
	end

	z0_gr = z0_ks * Ks;
%	c
	z0    = z0_gr;
	
	return