unwanted patterns in simplex noise

I want to create a "river biome" where there are rivers cutting to a flat land mass, to start I wrote a little js to generate a random height map (with simplex noise) but that's where I'm stuck.

this is what it generates:

as you can see there are clear diagonal lines in there. I tried looking up how to fix this and on my search I found these:

I don't know if this is my problem of if it's something else entirely.

here's the significant part of my code:

for(var y = 0;y < myRivers.height;y++){
for(var x = 0;x < myRivers.width;x++){
lightness = simplexnoise(x/50,y/50); // number between -1 and 1
myRivers.context.fillStyle = lightnessToRgb(lightness); //maps lightness to a color
myRivers.context.fillRect(x * 4, y * 4, 4, 4); // fills a pixel with the color
}
}


a codepen: https://codepen.io/anon/pen/gooyMj

• The second question you link to has a good analysis. What happens when you look at just 1 octave of the noise? Also, what interpolation function are you using? Linear interp will look more blocky than using a smooth step, for example. Commented Jan 9, 2018 at 6:45
• I don’t really use interpolation I think Commented Jan 9, 2018 at 8:21
• @user1118321 so multiplying with another octave might work? Commented Jan 9, 2018 at 8:22
• A heightmap generated from Perlin noise won't give you a plausible-looking river system anyway. Rivers "cut" their own valleys through terrain. Commented Jan 9, 2018 at 13:44
• No, I'm not suggesting a solution. I'm suggesting a way of determining what the problem is. If you show just your lowest octave, what does it look like? Is it blocky? I don't enough about how the simplexnoise() function you're using works to tell you. Is that a function you wrote or something supplied by a library? Commented Jan 9, 2018 at 16:56