Interpolate along the length of a river with 'diffusion interpolation with barriers'

Discussion created by shopk on Mar 27, 2013
Latest reply on Apr 3, 2013 by shopk
I'm involved with a project where I'm tasked with interpolating water quality data along a winding river (around 500km long but with a focus of a ~100km reach). I'm working mostly with phosphorus concentration values ranging from 0.0015-9.413 The data comes from water quality monitoring stations that I have snapped to within the river boundary (which I have been using as a break line). These stations are fairly sporadically spaced, some are within a few hundred meters but there are long stretches of several km without data.

I've been asked for a number of interpolations that span the majority of the river length but have run into some problems.
After doing some research the interpolation method most recommended for this type of problem seems to be  'diffusion interpolation with barriers'. I've run a number of test interpolations with small sections of the river with test points spaced much closer than most of the actual monitoring stations . I've played with various settings within the tool including various bandwidth values but have run into a problem where the resulting raster contains long stretches without data (as seen in the attached .png). The ideal output would encompass the majority of the river without any gaps in the interpolated raster. How would I fix this problem? Is it simply a matter of further increasing the bandwidth size (I've done tests with bandwidth values ranging from  10-10,000)?