5 to about 4 0 inches for increased sediment containment volume the ridges are spaced apart ridge to ridge in the length direction preferably from about 0 25 inches to about 8 inches with greater spacing for thicker mats the ridges and troughs form a three dimensional corrugated body structure 14 which serves to add strength and stability to the mat 10 the corrugated body structure 14 in combination with the bottom layer 12 forms a plurality of parabolic chambers 28 therebetween which serve to provide protected regions for filtering and trapping sediment referring once again to fig3 the top layer 18 is integrally secured on an upper side 20 of the corrugated body structure 14 adjacent to the ridges 46 of the corrugated body structure the top layer 18 is interwoven with the ridges and bridges over the troughs 48 of the corrugated body structure 14 to form additional parabolic chambers 32 on the upper side of the corrugated body structure 14 to trap additional sediment therein the top layer 18 also structurally supports the underlying corrugated body structure 14 to reduce stretching and flattening of the ridges 46 and troughs 48 during installation and prolonged use in its intended environment finally the top layer 18 protects captivated sediment from flow induced shear forces by creating a shear plane along the upper boundary of the mat according to an alternative configuration the top layer may be embodied as a plurality of strands 60 preferably made of polypropylene or polyethylene that run in the machine direction md and are spaced from one another across the width of the mat see fig5 the md strands act as reinforcing tendons and or shrinker yarns to assist in formation of the corrugated center layer through calendaring as is discussed.