We can import the schema for the schema via the [wsdl:]import element:

<wsdl:definitions ...>

<wsdl:import namespace="http://www.smallx.com/services/tideinfo/2005" 
             location="http://www.smallx.com/tideinfo-service/tideinfo.xsd"/>

</wsdl:definitions>

This makes the element declarations and types available to the WSDL definitions.