# vol\_dp\_a The parameters [vol\_area\_co](/io-docs/introduction-1/wetlands/hydrology.wet/vol_area_co.md), vol\_dp\_a and [vol\_dp\_b](/io-docs/introduction-1/wetlands/hydrology.wet/vol_dp_b.md) are coefficients that control how strongly the wetland surface area changes as storage volume changes relative to principal storage. They are used for wetland initialization and to update wetland area for each simulation time step. vol\_dp\_a and [vol\_dp\_b](/io-docs/introduction-1/wetlands/hydrology.wet/vol_dp_b.md) are used to infer wetland depth from current storage volume. They are not used independently in a physically transparent way but rather interact through the quadratic. If vol\_dp\_a is smaller than [vol\_dp\_b](/io-docs/introduction-1/wetlands/hydrology.wet/vol_dp_b.md), the wetland surface area shrinks more strongly when water volume declines. If vol\_dp\_a is larger than [vol\_dp\_b](/io-docs/introduction-1/wetlands/hydrology.wet/vol_dp_b.md), the wetland keeps a larger surface area even at lower storage. [vol\_area\_co](/io-docs/introduction-1/wetlands/hydrology.wet/vol_area_co.md) is used to convert the wetland depth to wetland area. The final area is clipped between 0.01 and 1.0, so the effect of extreme values of [vol\_area\_co](/io-docs/introduction-1/wetlands/hydrology.wet/vol_area_co.md), vol\_dp\_a, and [vol\_dp\_b](/io-docs/introduction-1/wetlands/hydrology.wet/vol_dp_b.md) may get hidden by those limits. The wetland area affects seepage, groundwater exchange, depth/release calculations, and constituent settling. --- # 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/vol_dp_a.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.