  Choosing ${\kappa}$ (horizontal ordinate of the saddle point associated to
the homoclinic orbit) as bifurcation parameter, bifurcations of the travelling
wave solutions is studied in a perturbed $(1 + 1)$-dimensional dispersive long
wave equation. The solitary wave solution exists at a suitable wave speed $c$
for the bifurcation parameter ${\kappa}\in (0,1-\frac{\sqrt3}{3})\cup
(1+\frac{\sqrt3}{3},2)$, while the kink and anti-kink wave solutions exist at a
unique wave speed $c^*=\sqrt{15}/3$ for $\kappa=0$ or $\kappa=2$. The methods
are based on the geometric singular perturbation (GSP, for short) approach,
Melnikov method and invariant manifolds theory. Interestingly, not only the
explicit analytical expression of the complicated homoclinic Melnikov integral
is directly obtained for the perturbed long wave equation, but also the
explicit analytical expression of the limit wave speed is directly given.
Numerical simulations are utilized to verify our mathematical results.
