Path of a signal traveling on a mismatched transmission line
You have not given any data how far from each other your drawn lines are placed - are they parallel and what are the geometric forms of the lines. Thus we have no idea what the structure between points O and L actually is.  

If one assumes the lines are straight, they are parallel, they are made of lossless 50 Ohm coaxial cable and they are so near each other that the resulted structure is a shorted transmission line he can guess the characteristic impedance of the coaxial cable pair is more than 50 Ohm. The guess is based on reduced capacitance per unit length. It's a guess because I cannot calculate what's caused by the dispersion - the wave propagates partially in the insulation of the coaxial cables and partially in the free space around the coaxial cables with higher speed.

But the input impedance seen by the feeding cable (not drawn) must be zero or infinite or a pure reactance which depends on the frequency and the length L. Nothing else is possible because these are the options which can create 100% reflection.

The feeded wave reflects partially at point O and the rest is reflected from the short circuit. Because the joint at O is not matched, the reflected wave partially continues to the feeding line and partially returns to the right to be re-reflected by the short. 

Your drawn structure is a resonator and at resonance frequencies your feeding line sees zero or infinite Ohm, at other frequencies there's a reactance which is non-predictable without geometric &amp; material data and frequency. If the data were given, the characteristic impedance  of your coaxial cable pair could be calculated but the calculation is beyond the scope of this answer.