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Hydraulics Lab: 2006-2007

Drop Flow Debris Filter (Part II)


Full modeling report


The Drop Flow Debris Filter is a stormwater Best Management Practice that was modeled in the UNM Open Channel Hydraulics Lab. A large-scale model was built in the three-foot flume to be able to visually observe the flow patterns that either deposit or remove debris from the basin. Several modifications were performed that changed the layout of the two parallel plates. A final design was proposed based on an assumed flow of 150 cubic feet per second.



Figure 1: The experimental set-up for testing the DFDF.


Recommendations and Conclusions

1.      The plates should be closer together in the basin than where the water exits the structure (Figure 15). This will keep the debris from becoming stuck inside the structure where it cannot be easily removed.

2.      The bottom plate should be slightly angled down towards the rear of the basin. This will eliminate the re-suspension of debris and better retain debris of all types.

3.      Add the additional storage to the sides of the basin. This will increase debris storage capacity and improve the debris detainment rate. These are solely extensions of the storage basin on either side. A vehicle access ramp could also be added to access the basin for debris removal.

  1. The addition of a small, screened area at the end of the debris basin is recommended. The first purpose would be to drain the basin at low flows, and the second would be to allow the structure to empty after a storm event to prevent standing water for mosquito breeding.



Figure 2: A conceptual model showing all the recommendations



COMPLETED PROJECT: River Elevation Modeling: An Integrated HEC-RAS ArcGIS Approach


Full modeling report



River elevation modeling is the prediction of surface water elevation based on flow rate, channel geography, surface parameters and boundary conditions.  It is a task typically performed by hydrologic modeling software, the most common of which is the Hydrological Engineering Center’s River Analysis System (HEC-RAS).  HEC-RAS requires numerous, vertical cross sections of the channel, which have traditionally been acquired through field surveys.  The resulting output was manually mapped to produce floodplain extents and water depths.  The process, while generally accurate and powerful, is time consuming and expensive.


This paper explores an alternative process which loosely integrates HEC-RAS with ArcGIS via an extension, HEC-GeoRAS.  GeoRAS can be used in combination with a high resolution digital terrain map of the channel and floodplain to extract the cross section information required from within the ArcMap environment, convert and export the data to HEC-RAS, an finally import the HEC-RAS output back into ArcMap for the creation of floodplain extents and water depth grids.


The procedure is outlined through application to a test case, a mile long stretch of the Calabacillas Arroyo, an intermittent, natural drainage channel just northwest of Albuquerque, NM.  The procedure is demonstrated to work quickly and effectively, although limitations apply to many channels because of lack of high-resolution data or perennial flow that masks the topology of the channel bottom.