Excerpt from CRAFS™  patent ...

CLAIM 1 :  CRAFS™ provides a much greater seepage rate of the SLF it retains and filters through the system across a given flow path (i.e., sediment retention zone, a.k.a. SRZ)  than a conventional sediment control system (CSCS) is capable of while spanning an identical flow path of SLF.  And the CRAFS™  provides equivalent retention efficiency of particle matter from the fluid passing through the system than a  CSCS spanning the same flow path.

CRAFS™  corrugated structure  will yield a greater area of geotextile for retention, filtration, and seepage (ARFS) than available from a CSCS spanning the same SLF flow path.   CRAFS™ continuous corrugated structure spans a sediment retention zone (SRZ) with a series of adjacent “V” shaped containment units ("VCU", a.k.a. Retention & Filtration Wedges)  each connected at their upstream vertexes.   These VCU retain the SLF against  the filter medium on its upstream side.  The series of adjacent VCU (a.k.a: Retention & Filtration Wedges) created by a CRAFS™  has several times more area for retention and seepage of the SLF  than a Linear RAF spanning the same width of  SRZ.  

A test for performance comparisons between CSCS and CRAFS™  (i.e., Slurry R-F-S Test)  was developed to evaluate performance of the CSCS and the CRAFS™  under control conditions, and to identify any  measurable  performance differences between the two systems.  (see Appendix A: “Test Method Summary” …  not accompanying this excerpt).                                               

The Slurry R-F-S Test Apparatus  simulates overland flow down a slope by the release of  a soil particle / water slurry mixture of 50,000 ppm down a flume on a 37 degree angle from horizontal.  The SLF released is retained by both a CSCS and a CRAFS™.. The CSCS has a linear span of the flow channel of 18” and total ARSF of 144 sq. in. (0.0929 sq.m.)

The corrugated geometry of the CRAFS™ in this test method has a downstream vertex with an acute angle of 74 degrees, and extensions from the vertex going 15” (38.1 cm)  up slope to the adjacent walls of the flume.  Total surface area of the CRAFS™  is this test is 15 “ X 8” X 2 = 240 sq in which is 1.66 times more surface area that the CSCS .  

Note that the  ARFS   for a CRAFS™ in  real world  conditions of use are likely to provide a  much greater percentage of area for retention, filtration, and seepage over that of a CSCS spanning the same SRZ.  As a result, the CRAFS™  is able to provide much greater performance benefit over a CSCS.   This test method was only developed to provide lab scale results using the system dimensions noted above to measure any noticeable performance differences between the CSCS and a CRAFS™  to support performance claims.

Hydraulic Head Causing Seepage                                                                                                                                                         In all tests run to date, roughly half of the maximum  geotextile height in both the CSCS and the CRAFS™ is exposed to the SLF it retains.  This is true for this test as well as real world conditions for SLF runoff retained by both systems.  (See photos in Appendix A: “Test Method Summary”... not accompanying this excerpt).   The hydraulic head causing seepage through the AFRS of the  CSCS is constant across the geotextile's 18” width.  

The CRAFS™ corrugated geometry results in a variable hydraulic head of SLF adjacent to the geotextile on the system with the maximum head at the downstream vertex and the head equal to zero just above the fabric connection at the “upstream” sidewalls of the flume.

Despite this “variable hydraulic head” retained upstream of the CRAFS™  within the flume, its greater ARFS (>169% that of the CSCS)  results in a more rapid filtered seepage of the retained SLF through the CRAFS™  than through the CSCS .  Before the first tests were run there was some concern for extreme hydraulic head  in the CRAFS™  systems because their area and subsequent volume of retention upstream  was less than that of a CSCS .  But overflow was never experienced because the rate of seepage through the CRAFS™ was significantly faster than that for all the CSCS tested.

The photos referred to below show the varied levels of the retained SLF at different lapsed times during one series of the tests on a CSCS  and a CRAFS™.  (excerpt C1-1)

Discussion of Slurry R-F-S Test Results                                                                                                                                                
Preliminary results  illustrated by Figure C1-4 a&b, Figure C1-5 a&b, and Figure C1-6 a&b show similar results to all tests run to date, i.e., the  CRAFS™ structure has significantly  faster system seepage rate through the the SRZ than the CSCS tested.  (figures referenced are accompanying this excerpt)

Figures C1-4 a & b show the SLF level upstream of the geotextile approximately 2 to 3  minutes after its initial load of the original 10 liter slurry of SLF.  Prior to and during “initial contact of the SLF into the RAFS,  the SLF deposited a significant amount of its sediment load along the base of the flume just upstream from the geotextile.  This is similar to normal field conditions where runoff is retained, reaches a static state, and begins sediment deposition before it reaches the  retention medium in its flow path.  

The hydraulic head at the downstream vertex of the CRAFS™  is slightly higher  upon “initial contact” than the hydraulic head adjacent to the CSCS.  But the CRAFS™  demonstrates a more rapid rate of filtered seepage than the CSCS, so its drainage and draw down in hydraulic head is much faster.  Note the volume of retained SLF for the CSCS demonstrated at various times in these photos.   

Figures C1-5a & C1-5b show the test run “1 Hour after the initial slurry impact” for the CSCS and the CRAFS™.  The CSCS has drained less than 1/3 of its total retained SLF (< 3.3 liters), while the CRAFS™ has drained approximately 2/3 of its total retained SLF (~6.7 liters).  This comparison reveals the initial seepage through the CRAFS™  is roughly double that of the CSCS with AFRS only 1.69 times that of the CSCS tested.

Figures C1-6a & C1-6b  show the CRAFS™  and the CSCS at or near complete dewatering of the their retained SLF.  Note the “elapsed time for complete drainage in each system  is dramatically different.  Complete drainage of the CSCS took more than 4 hours (>240  minutes) following “initial impact”,     while the CRAFS™  drained completely at only 74 minutes following “initial impact”.  The CRAFS™  total dewatering occurs in less than 1/3 the time required for the CSCS (i.e.,  74 min / >240 min  =  < 1/3 the time).

Conclusion from Preliminary Test Results ... Slurry R-F-S Test on CSCS and CRAFS™  run to date show the CRAFS™  tested allowed a much greater rate of filtered seepage through a given sediment retention zone (SRZ) normal to the direction of flow of a sediment laden fluid (SLF) than a CSCS allowed through the same  SRZ.

The retained SLF upstream of both RAFS and its filtered effluent passing through the system were air dried and weighed. Measurements of retained and effluent particles were comparable, both indicating high retention efficiency, i.e.,retaining more than 95 % of the sediment particles originally poured onto the upstream segment of the flume.(excerpt C1-2)