Volume 2-05, Chapter 3 - City of Wichita
Volume 2-05, Chapter 3 - City of Wichita Volume 2-05, Chapter 3 - City of Wichita
Section 3.2.10 - Stormwater Wetland planting sites and backfill these with uncompacted topsoil. However, these features must not be located within the tree exclusion area, and must not violate the groundwater clearance requirements. J. ADDITIONAL SITE-SPECIFIC DESIGN CRITERIA AND ISSUES Physiographic Factors - Local terrain design constraints Low Relief: Providing wetland drain can be problematic. High Relief: Embankment heights restricted Karst: Requires poly or clay liner to sustain a permanent pool of water and protect aquifers; limits on ponding depth; geotechnical tests may be required. Soils • Hydrologic group ‘A’ soils and some group ‘B’ soils may require liner. Special Downstream Watershed Considerations Aquifer Protection: Inflow of untreated hotspot runoff not permitted. May require liner for type “A” and some “B” soils. Five foot minimum clearance above historical high groundwater for unlined wetlands, 2 feet for lined. 3.2.10.6 Design Procedures Step 1 Step 2 Step 3 Step 4 Compute runoff control volumes from the integrated design approach. Calculate the WQ v . See Chapter 1 and Chapter 4. Confirm local design criteria and applicability. Consider any special site-specific design conditions/criteria. Check with local officials and other agencies to determine if there are any additional restrictions and/or surface water or watershed requirements that may apply. Determine pretreatment volume A sediment forebay is provided at each inlet, unless the inlet provides less than 10% of the total design storm inflow to the pond. The forebay should be sized to contain 0.1 acre-inch per impervious acre of contributing drainage and should be 4 to 6 feet deep. The forebay storage volume counts toward the total WQ v requirement and may be subtracted from the WQ v for subsequent calculations. Allocate the WQv volume among marsh, micropool, and extended detention volumes. Page 3 - 138 Volume 2, Technical Guidance
Section 3.2.10 - Stormwater Wetland Use recommended criteria from Table 3-8. Step 5 Step 6 Step 7 Step 8 Step 9 Determine wetland location and preliminary geometry, including distribution of wetland depth zones. This step involves initially laying out the wetland design and determining the distribution of wetland surface area among the various depth zones (high marsh, low marsh, and deepwater). Set WQ v permanent pool elevation (and WQ v -ED elevation for extended detention shallow wetland) based on volumes calculated earlier. Compute extended detention orifice release rate(s) and size(s), and establish CP v elevation. Shallow Wetland: The CP v elevation is determined from the stage-storage relationship and the orifice is then sized to release the channel protection storage volume over a 24 hour period. The channel protection orifice shall be adequately protected from clogging by an acceptable treatment as shown in Chapter 5, or a similar treatment at the discretion of the site engineer. A reverse slope pipe attached to the riser, with its inlet submerged 1 foot below the elevation of the permanent pool is a recommended design. ED Shallow Wetland: Based on the elevations established in Step 5 for the extended detention portion of the WQ V , the water quality orifice is sized to release this extended detention volume in 24 hours. The water quality orifice shall be adequately protected from clogging by an acceptable treatment as shown in Chapter 5, or a similar treatment at the discretion of the site engineer. A reverse slope pipe attached to the riser, with its inlet submerged one foot below the elevation of the permanent pool, is a recommended design. The CP v elevation is then determined from the stage-storage relationship. The invert of the channel protection orifice is located at the water quality extended detention elevation, and the orifice is sized to release the channel protection storage volume over a 24 hour period. Calculate the flood control release rates and water surface elevations. Set up a stage-storage-discharge relationship for the control structure for the extended detention orifice(s) and the flood control storms. Route floods through facility and adjust accordingly to achieve peak flow control. Design embankment(s) and spillway(s). Size the emergency spillway by routing 100-year flood through the spillway in accordance with the previously discussed criteria. Set the top of dam elevation based on a minimum of 1 foot of freeboard. At final design, provide safe passage for the 100-year event. Investigate potential pond/wetland hazard classification. Volume 2, Technical Guidance Page 3 - 139
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Section 3.2.10 - Stormwater Wetland<br />
Use recommended criteria from Table 3-8.<br />
Step 5<br />
Step 6<br />
Step 7<br />
Step 8<br />
Step 9<br />
Determine wetland location and preliminary geometry, including distribution <strong>of</strong><br />
wetland depth zones.<br />
This step involves initially laying out the wetland design and determining the<br />
distribution <strong>of</strong> wetland surface area among the various depth zones (high marsh, low<br />
marsh, and deepwater). Set WQ v permanent pool elevation (and WQ v -ED elevation<br />
for extended detention shallow wetland) based on volumes calculated earlier.<br />
Compute extended detention orifice release rate(s) and size(s), and establish CP v<br />
elevation.<br />
Shallow Wetland: The CP v elevation is determined from the stage-storage<br />
relationship and the orifice is then sized to release the channel protection storage<br />
volume over a 24 hour period. The channel protection orifice shall be adequately<br />
protected from clogging by an acceptable treatment as shown in <strong>Chapter</strong> 5, or a<br />
similar treatment at the discretion <strong>of</strong> the site engineer. A reverse slope pipe attached<br />
to the riser, with its inlet submerged 1 foot below the elevation <strong>of</strong> the permanent pool<br />
is a recommended design.<br />
ED Shallow Wetland: Based on the elevations established in Step 5 for the<br />
extended detention portion <strong>of</strong> the WQ V , the water quality orifice is sized to release<br />
this extended detention volume in 24 hours. The water quality orifice shall be<br />
adequately protected from clogging by an acceptable treatment as shown in <strong>Chapter</strong><br />
5, or a similar treatment at the discretion <strong>of</strong> the site engineer. A reverse slope pipe<br />
attached to the riser, with its inlet submerged one foot below the elevation <strong>of</strong> the<br />
permanent pool, is a recommended design. The CP v elevation is then determined<br />
from the stage-storage relationship. The invert <strong>of</strong> the channel protection orifice is<br />
located at the water quality extended detention elevation, and the orifice is sized to<br />
release the channel protection storage volume over a 24 hour period.<br />
Calculate the flood control release rates and water surface elevations.<br />
Set up a stage-storage-discharge relationship for the control structure for the<br />
extended detention orifice(s) and the flood control storms. Route floods through<br />
facility and adjust accordingly to achieve peak flow control.<br />
Design embankment(s) and spillway(s).<br />
Size the emergency spillway by routing 100-year flood through the spillway in<br />
accordance with the previously discussed criteria. Set the top <strong>of</strong> dam elevation<br />
based on a minimum <strong>of</strong> 1 foot <strong>of</strong> freeboard.<br />
At final design, provide safe passage for the 100-year event.<br />
Investigate potential pond/wetland hazard classification.<br />
<strong>Volume</strong> 2, Technical Guidance Page 3 - 139
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