# dp\_ps The average depth of water at principal spillway is used to calculate the principal volume of the wetland and to set the default weir height (if the weir height is specified in column [height](/io-docs/introduction-1/reservoirs/weir.res/vel_co.md) in [**weir.res**](/io-docs/introduction-1/reservoirs/weir.res.md), this value will override the default weir height calculated based on dp\_ps). The principal volume of the wetland is used during daily wetland simulation in the equation that updates surface area as storage changes and for wetland release conditions and actions. --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://swatplus.gitbook.io/io-docs/introduction-1/wetlands/hydrology.wet/dp_ps.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.