hello
I am not sure to understand your plot and where the transition land / water can be seen
nevertheless , if you need to smooth a 2D surface , I like the two following Fex submissions
code
clear all
dep=load('dep_shoal_inlet.txt');
[n,m]=size(dep);
dx=2.0;
dy=2.0;
x=[0:m-1]*dx;
y=[0:n-1]*dy;
x_sponge=[0 180 180 0 0];
y_sponge=[0 0 y(end) y(end) 0];
x_wavemaker=[240 260 260 240 240];
y_wavemaker=[0 0 y(end) y(end) 0];
wid=5;
len=6;
set(gcf,'units','inches','paperunits','inches','papersize', [wid len],'position',[1 1 wid len],'paperposition',[0 0 wid len]);
clf
figure(1),
pcolor(x,y,-dep),shading flat
cbar=colorbar;
set(get(cbar,'ylabel'),'String',' -dep (m) ')
hold on
plot(x_sponge,y_sponge,'g--','LineWidth',2)
text(10,1000,'Sponge','Color','g')
plot(x_wavemaker,y_wavemaker,'w-','LineWidth',2)
text(270,1200,'Wavemaker','Color','w')
caxis([-10 3])
xlabel('x (m)')
ylabel('y (m)')
% print -djpeg inlet_shoal.jpg
% smoothn : Fex : https://fr.mathworks.com/matlabcentral/fileexchange/25634-smoothn?s_tid=ta_fx_results
deps = smoothn(dep,1e5);
figure(2),
pcolor(x,y,-deps),shading flat
% smooth2a : Fex : https://fr.mathworks.com/matlabcentral/fileexchange/23287-smooth2a?s_tid=srchtitle
deps2 = smooth2a(dep,25,25);
figure(3),
pcolor(x,y,-deps2),shading flat
