Overview <ul><li>Harris County has identified an approximately one mile segment of Independence Parkway in Precinct Two to be improved from a two lane roadway with ditches to a four lane thoroughfare. Implementation of Low Impact Development (LID) measures will help decrease storm water flows and will enhance the storm water quality. Our design utilizes pervious paving at the roadway shoulders, small bioswales (in lieu of open ditches) at each outside edge, and a large-center bioswale that has been recessed to accommodate a walking/bicycling trail. </li></ul>07188
Project Stars 07188 Monument Trail has been designed with Harris County’s Project Stars program in mind. Locations along the roadway have been reserved for historic markers to identify significant events and locations.
<ul><li>Equally as important to cost and storm water quality/quantity reductions, Independence Parkway plays a vital role in the history of the area and has been identified as the most significant site by Project Stars. The proposed roadway design for the new 4 lane thoroughfare has incorporated a bicycling/walking trail into its center Bioswale-median. Trail users are provided with an opportunity to experience and observe the rich history of Texas. Some of the historically significant sites and elements that surround the new trail/thoroughfare include the San Jacinto Monument, San Jacinto Battleground, Battleship Texas, and the Lynchburg Ferry. The proposed design solution for the roadway expansion addresses the multiple storm water concerns and provides a new means for everyone to experience the area’s historic sites. </li></ul>07188
Key Results for Proposed Plan <ul><ul><li>Assumes 85% Impervious Area (CN = 95) </li></ul></ul><ul><ul><li>LID Measures (Bioswales) reduce flow velocities to 1.7 ft/sec </li></ul></ul><ul><ul><li>LID Measures Extend Flow Paths by routing portions of the flows into roadside bioswales, then directing flows to a median bioswale </li></ul></ul><ul><ul><li>Net result is LOWER PEAK RUNOFF RATES </li></ul></ul><ul><ul><li>Meets Harris County’s Water Quality requirements </li></ul></ul><ul><ul><ul><li>Eliminates the need to route flows through trash racks </li></ul></ul></ul><ul><ul><ul><li>Eliminates the use of credits in the County’s Water Quality Mitigation Bank. </li></ul></ul></ul><ul><ul><ul><li>Provides enhancement directly for this area </li></ul></ul></ul>07188
Hydrologic Model <ul><li>The SCS Method has been used to develop hydrographs based upon 24-hour rainfall depths. The 24-hour rainfall depth is typically used to evaluate detention requirements for an area. Rainfall depths used in the documentation provided are 5.2-inches for the 5-year, 7.1-inches for the 10-year, and 12.4 inches for the 100-year storm events. These rainfall depths do not correspond to the depths used in for that area (Region 3) as shown within the White Papers from the Tropical Storm Allison Recovery Project. The same rainfall depths provided within the competition documentation have been used for this evaluation. </li></ul>07188 Click for report
<ul><li>The highly effective in line storm water mitigation/design for this project should reduce infrastructure and land costs by eliminating the need for large scale, expensive, and unsightly offsite detention ponds. Hydraulic computations reveal that storm water velocities in the proposed design solution are lower than that of the existing conditions. Computations assume that the existing roadway is approximately 50% impervious and has storm water velocities that average approximately 2 feet per second. The proposed four lane roadway is approximately 85% impervious. The new roadway exhibits a reduction in peak storm water flows, resulting from a decreased time of concentration while maintaining similar storm water runoff coefficients (Curve Numbers). </li></ul>07188
Cost Comparison <ul><li>The reduction in overall storage volume allows for reasonable design of inline detention within the roadside ditches and/or within the median, which provides a cost savings to the County by elimination the need for offsite detention. This cost savings should offset the cost of any of the more costly features in our proposed design. We believe the cost of the proposed road would be very competitive with traditional roadways. </li></ul>07188