  We compare some first order well-balanced numerical schemes for shallow water
system with special interest in applications where there are abrupt variations
of the topography. We show that the space step required to obtain a prescribed
error depends on the method. Moreover, the solutions given by the numerical
scheme can be significantly different if not enough space resolution is used.
We shall pay special attention to the well-known hydrostatic reconstruction
technique where it is shown that large bottom discontinuities may be neglected
and a modification is proposed to avoid this problem.
