Changes

The drawdown time in the pond can be estimated using the classic falling head orifice equation which assumes a constant pond surface area<ref>Ontario Ministry of Environment. (2003). Stormwater Management Planning and Design Manual. Retrieved January 15, 2017, from https://www.ontario.ca/document/stormwater-management-planning-and-design-manual/stormwater-management-plan-and-swmp-design</ref>. This assumption is generally not valid, and a more accurate estimation can be made if the equation is solved as a differential equation. This is easily done if the relationship between pond surface area and pond depth is approximated using a linear regression:

The drawdown time in the pond can be estimated using the classic falling head orifice equation which assumes a constant pond surface area<ref>Ontario Ministry of Environment. (2003). Stormwater Management Planning and Design Manual. Retrieved January 15, 2017, from https://www.ontario.ca/document/stormwater-management-planning-and-design-manual/stormwater-management-plan-and-swmp-design</ref>. This assumption is generally not valid, and a more accurate estimation can be made if the equation is solved as a differential equation. This is easily done if the relationship between pond surface area and pond depth is approximated using a linear regression:

<math>A_O=\frac{2A_{P}}{t\ C(2g^{0.5})}\left ( h_{1}^{0.5}-h_{2}^{0.5} \right )</math>

<math>A_o=\frac{2A_{P}}{t\ C(2g^{0.5})}\left ( h_{1}^{0.5}-h_{2}^{0.5} \right )</math>

{{plainlist|1=Where

{{plainlist|1=Where

* t = Drawdown time (s)

* ''t'' = Drawdown time (s)

* A_p = Surface area of the pond(m²)

* ''A_p'' = Surface area of the pond(m²)

* C = Discharge coefficient (typically 0.63)

* ''C'' = Discharge coefficient (typically 0.63)

* A_O = Cross-sectional area of the orifice(m²)

* ''A_o'' = Cross-sectional area of the orifice(m²)

* g = Gravitational acceleration constant (9.81 m/s²)

* ''g'' = Gravitational acceleration constant (9.81 m/s²)

* h₁ = Starting water elevation above the orifice (m)

* ''h₁'' = Starting water elevation above the orifice (m)

* h₂ = Snding water elevation above the orifice (m)}}

* ''h₂'' = Snding water elevation above the orifice (m)}}

C2

C2