ECIV 562
USC: DOP Meadows
Spring 2007
Design Challenge – This is 40% of your final exam. You may work in teams on this assignment.
Due: Monday, 7 May 2007 @ 9 a.m.
Your company has been hired to design and obtain the construction permits for stormwater and sediment control ponds as part of new development at two locations within the Hawkins Branch watershed in NorthernRichlandCounty. This pond is to be constructed near the outfall from a residential subdivision; any pond discharge will go into Hawkins Branch, which is a natural channel that must be preserved in its present condition—to the extent possible—per the following stormwater management regulations.
No Net Increase Provisions
No net increase in nonpoint source pollution – Stormwater control systems shall be designed so that there is no degradation of water quality in the receiving watercourse.
No net increase in sediment loadings – Stormwater control systems shall be designed to reduce, to the maximum extent possible, the total sediment loadings onto downstream watercourses from a development site to a level compliant with predevelopment sediment loadings.
No net increase in stormwater runoff rates and stream channel erosion – Stormwater control systems shall be designed so that, to the maximum extent possible, the post-development runoff rates from the site are no greater than predevelopment rates.
No net increase in stormwater runoff volumes – Stormwater control systems shall be designed so that, to the maximum extent possible, the post-development runoff volumes from the site are no greater than predevelopment volumes.
South Carolina counties and towns don’t have such regulations in place, but similar regulations, such as the 10% rule exist in some counties and towns. The extent of such regulations is expected to grow, perhaps not too far in the future.
Your team has been assigned two points on the attached GIS map that define the outlets for stormwater runoff from planned residential subdivisions. Use available GIS maps, printed maps, on-line resources, etc, to develop necessary data and other input for your analysis and design. Use the on-line accessible spreadsheets developed specifically for this application to simulate the runoff hydrographs, to design ponds and evaluate their performance, and to assess the net impact on the downstream receiving pond, i.e., the terminal in-stream pond. As an absolute minimum, you must not increase the post-development peak inflow to the in-stream pond above the predevelopment rate for the design storm. Evaluate what should be done, in terms of pond design, to maintain the post development inflow volume at or below the predevelopment volume. Write a memo report summarizing your approach for analysis and design, your findings, and recommendations.
Everyone on each team must contribute her/his proportional share. Part of your individual score for this assignment shall be the results of a peer evaluation.
Team 1: Points 1 and 4
Team 2: Points 2 and 4
Team 3: Points 3 and 4
Team 4: Points 1 and 2
Team 5: Points 2 and 3
Team 6: Points 3 and 4
When building your watershed scale simulation model, use a link-node diagram as your schematic outline or flowchart. Nodes represent points of outflow from a watershed, points of inflow and outflow from a pond or channel, and points were two or more channels confluence. Links represent ponds and channel reaches, i.e., drainage system elements through which hydrographs are routed. The following example discusses the link-node diagram for drainage system that includes runoff from residential development discharging into Hawkins Branch at nodes 1 and 4. We will draw the link-node diagram in class.
First assign a label to each subwatershed, such as:
Watershed ID / Dischages into Hawkins Branch at node / Has a pond? / General Description101 / 1 / Yes / Residential subdivision
102 / 1 / No / Natural area. This is the area that drains to the point labeled 2 on the Hawkins Branch GIS map, but those numbers indicate points of outflow from residential subdivisions. Since, for this example, watershed 102 will not be developed, assume the runoff hydrograph combines with the outflow hydrograph from the pond for watershed 101 at node 1.
103 / 4 / No / Natural area. This is the area that drains to Hawkins Branch along the reach between nodes 1 and 4. Because it largely is distributed lateral inflow that you compute as a single subwatershed runoff hydrograph, indicate the stormwater hydrograph inflows to Hawkins Branch at the downstream end of the reach at node 4.
104 / 4 / Yes / Residential subdivision
105 / 6 / No / Natural area. This is the area that drains to the unnamed tributary and onfluences with Hawkins Branch upstream of the pond created by the beaver dam. This area is upstream of and does not include any of Stonington.
106 / 6 / No / Natural area. This is the area that drains to Hawkins Branch along the reach between nodes 4 and 6. Indicate stormwater from this area inflows to Hawkins Branch at the downstream end of the reach at node 6.
Next, assign routing functions and upstream and downstream (inflow and outflow) nodes.
Routing Function / Upstream Node / Downstream Node / General DescriptionPond / 11 / 1 / Stormwater pond for Watershed 101. Route the runoff hydrograph from watershed 101 through this pond. Add the pond outflow hydrograph and the runoff hydrograph from watershed 102.
Channel / 1 / 4 / Route the added hydrograph from node 1 to node 4. Add the runoff hydrograph from watershed 103 to the channel routed hydrograph.
Pond / 14 / 4 / Stormwater pond for Watershed 104. Route the runoff hydrograph from watershed 104 through this pond. Add the pond outflow hydrograph to the combined hydrographs obtained by adding the runoff hydrograph from watershed 103 and the channel routed hydrograph.
Channel / 4 / 6 / Route the added hydrograph from node 4 to node 6. Add the runoff hydrographs from watersheds 105 and 106 to the channel routed hydrograph. The cumulative hydrograph will combine with the outflow hydrograph from the Stonington pond to simulate the total watershed runoff into the upper Hollis pond.