Difference between revisions of "Estimating and calculating bypass for the Minimal Impact Design Standards (MIDS) Calculator"
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| − | The Minimal Impact Design Standards (MIDS) Calculator can be used to design <span title="One of many different structural or non–structural methods used to treat runoff"> '''best management practices'''</span>. Typically, bmps are designed to meet a specific <span title="A performance goal specifies what level of stormwater treatment must be achieved"> '''performance goal'''</span>, such as the 1.1 inch MIDS standard or the 1 inch requirement in the Construction Stormwater General Permit. | + | = = |
| + | The Minimal Impact Design Standards (MIDS) Calculator can be used to design and size <span title="One of many different structural or non–structural methods used to treat runoff"> '''best management practices'''</span>. Typically, bmps are designed to meet a specific <span title="A performance goal specifies what level of stormwater treatment must be achieved"> '''performance goal'''</span>, such as the 1.1 inch MIDS standard or the 1 inch requirement in the Construction Stormwater General Permit. | ||
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| + | For infiltration practices in the calculator, runoff captured by a bmp is infiltrated. Remaining water bypasses the bmp and is not treated. | ||
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| + | For bmps with an underdrain (tree trench, bioretention, swale main channel), some water captured by the bmp is returned to the stormwater system via the underdrain. The calculator does not differentiate between water that bypasses the bmp and water returned via the underdrain, instead assuming all this water is treated. Similarly, for non-volume bmps (constructed pond, wetland, sand filter, wet swale), the calculator does not differentiate between water that has been treated and water that bypasses the bmp, instead assuming all runoff has been treated. This is shown in the adjacent image. This can result in significant errors in calculations of TSS and phosphorus, with the calculator overestimating pollutant removal. | ||
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| + | To correct this error, the BMP parameters tab on each of these seven bmps now asks the user to input a bypass %. The default is 0 percent, which assumes the BMP is sized to meet the MIDS performance goal. | ||
Revision as of 14:41, 8 June 2021
The Minimal Impact Design Standards (MIDS) Calculator can be used to design and size best management practices. Typically, bmps are designed to meet a specific performance goal, such as the 1.1 inch MIDS standard or the 1 inch requirement in the Construction Stormwater General Permit.
For infiltration practices in the calculator, runoff captured by a bmp is infiltrated. Remaining water bypasses the bmp and is not treated.
For bmps with an underdrain (tree trench, bioretention, swale main channel), some water captured by the bmp is returned to the stormwater system via the underdrain. The calculator does not differentiate between water that bypasses the bmp and water returned via the underdrain, instead assuming all this water is treated. Similarly, for non-volume bmps (constructed pond, wetland, sand filter, wet swale), the calculator does not differentiate between water that has been treated and water that bypasses the bmp, instead assuming all runoff has been treated. This is shown in the adjacent image. This can result in significant errors in calculations of TSS and phosphorus, with the calculator overestimating pollutant removal.
To correct this error, the BMP parameters tab on each of these seven bmps now asks the user to input a bypass %. The default is 0 percent, which assumes the BMP is sized to meet the MIDS performance goal.