//Hook up the ScrollViewer's ScrollChanged event
scrollViewer1.ScrollChanged += new ScrollChangedEventHandler(scrollViewer1_ScrollChanged);

//The ScrollChanged event handler
void scrollViewer1_ScrollChanged(object sender, ScrollChangedEventArgs e)
{
    //Here it simply syncs the WebControl to the ViewPort. You
    //may need to adapt it to fit your own scenario. For example,
    //you may need to hide a portion of or even the whole 
    //WebControl if it scrolls out of view
    WebControl1.SetValue(Canvas.TopProperty, scrollViewer1.VerticalOffset);
    WebControl1.SetValue(FrameworkElement.HeightProperty, scrollViewer1.ViewportHeight);
    WebControl1.SetValue(FrameworkElement.WidthProperty, scrollViewer1.ViewportWidth);

    //Here it syncs the WebControl's scroll position to the
    //ScrollViewer's scroll position. Again most likely you
    //will need to adapt it to fit your own scenario. For example,
    //you may need to add/substract certain offset to the
    //ScrollViewer's scroll offset. Note that the ScrollViewer's
    //offset is in WPF logical unit, but the WebView uses
    //device unit (pixel), so here we have to convert it
    PresentationSource source = PresentationSource.FromVisual(scrollViewer1);
    Matrix matrix = source.CompositionTarget.TransformToDevice;
    Point p = matrix.Transform(new Point(0, scrollViewer1.VerticalOffset));
    WebControl1.WebView.SetScrollOffset(0, (int)Math.Round(p.Y));
}