Jesin on "Twenty Thirteen Sidebar Overlapping Footer"

Add the following CSS code to the style.css of your child theme

#main {
  margin: 0 auto;
  min-height: 2950px;
  width: 1000px;
}

You'll have to modify the min-height value if you add or remove widgets in the sidebar.

You have an inline CSS code on the footer, remove that

<footer role="contentinfo" class="site-footer" id="colophon" style="margin-top: 1673px;">