At a recent tournament I ran, this situation came up for a ruling.
(I did take photos but I cannot work out how to load them and there is a very restrictive file size limit).
A column of 5 light horse were crossing a navigable river close to a bend in the river (on their left). The leading 2 elements had cleared the river; the third had its front edge clear, and rear edge in, the river; the 4th and 5th elements front edges were completely in the river. The left flank edges of the leading two elements were clear of the water, the 3rd was partially in the water.
An opposing Blade element made a front edge to side edge contact on the 2nd light horse element, and partial contact on the third. It did not enter the water due to the bend in the river.
If the river was not there, the 2nd and 3rd element would have turned to face. With the river there however, if they turned to face, the 2nd element rear left hand corner would be in the river and the 3rd element's left flank would be in the river, facing into the flow of the river.
With the river there, by doing this, they would have contradicted the rule on page 20, Water Features, which states "Rivers can also be crossed with more difficulty off-road at between 45 and 135 degrees to the flow by wading,..." So I ruled they could not turn to face combat. This is in contradiction to page 35 where it states in the first paragraph that an element contacted on its flank edge turns into full front edge contact.
It could be argued that, as per the 2nd paragraph on page 35 of Turning to Face Flank or rear contact, "If an element or elements contacted in flank... have insufficient room to turn to face, the enemy must move back to make room." In this case, the 2 light horse elements would turn to face, move forward out of the river, and the enemy Blade would move back. There was sufficient room for this. They would then be at -1 in combat as they can't recoil into the river. However, this manoeuvre involves going against the flow of the river.
My ruling was that the light horse cannot turn to face due to the flow of the river. The light horse (2nd in the column) would be attacked as a front edge contact in contact with an enemy flank edge. This is unusual but not disallowed I think. Expendables and routers are specifically ruled that they do not turn to face when contacted on the flank. With the front edge being in contact with the flank edge, and the blade winning the combat, the light horse was destroyed.
Was my interpretation of the rules correct?
On another point as I re-read the rules of this section:
it is not clear if the light horse suffer a -1 combat penalty for the flank edge contact. Page 35 after the first two bullet points states "An element...in front edge contact with the flank or rear edge of an enemy element which is fighting to its front is subject to an adverse tactical factor." However the tactical factors on page 37 do not mention having to be in front edge combat for this tactical factor to apply. I certainly have never played a rear edge contact penalty can only be applied if the element attacked is also in front edge combat. My interpretation is that the light horse would suffer a -1 combat penalty for being attacked on the flank.
Thank you for your assistance in this.