  Given a contact three manifold $Y$ with a nondegenerate contact form
$\lambda$, and an almost complex structure $J$ compatible with $\lambda$, its
embedded contact homology $ECH(Y,\lambda)$ is defined (arXiv:1303.5789) and
only depends on the contact structure. In this paper we explain how to compute
ECH for Morse-Bott contact forms whose Reeb orbits appear in $S^1$ families,
assuming the almost complex structure $J$ can be chosen to satisfy certain
transversality conditions (this is the case for instance for boundaries of
concave or convex toric domains, or if all the curves of ECH index one have
genus zero). We define the ECH chain complex for a Morse-Bott contact form via
an enumeration of ECH index one cascades. We prove using gluing results from
arXiv:2206.04334 that this chain complex computes the ECH of the contact
manifold. This paper and arXiv:2206.04334 fill in some technical foundations
for previous calculations in the literature (arXiv:1608.07988,
arXiv:math/0410061).
