A composite grain size distribution curve of the sediment samples collected from the
source shall be prepared. A composite gradation is the mean gradation of all material
sampled in the source area. If, by visual observation, individual samples appear
dissimilar in size and character, each distinctive area will be analyzed independently.
Stipulations may be given by BEACON on which borrow material from a site may be
used as beach fill.
Beach Fill with More than 10% Fines Proposed Criteria for the Program
The USACE (1989) stipulates that further testing to evaluate the chemical composition of
the material may be required if material contains more than 10% fines (silt and clay
passing the #200 sieve or less than 0.074 mm in diameter). BEACON proposes use of
material with between 20 to 35 % fines.
Beach Fill with More Than 10% Coarse Grains By Volume
Beach fill material with a relatively high percentage of coarse grains will only be
acceptable if the particles are no larger than cobble-sized, and do not constitute greater
than 10% of the volume of the beach fill, with the exception of Surfer's Point. Beach fill
material containing more than 10% cobble-sized particles is desirable for placement at the
Surfer's Point beach fill site because the existing beach sediment already contains a high
volume of cobble material (Refer to Section 3.4).
The proposed percentage of fine-grained sediment for the program (25% to 35%, depending on
the site) is relatively low compared to natural sediment delivery from streams in the region.
Also, the absolute quantity of fine-grained material proposed for beach placement over a year as
part of the program is well below the quantity of fines delivered annually from local streams.
Table 4.2 shows natural sediment delivery rates compared to those proposed by BEACON. The
table indicates that the annual quantity of fines proposed by BEACON for beach placement is
approximately 30% of that delivered by streams under existing conditions, and the total volume
of proposed material is approximately 62% of that delivered by streams annually. Streams
typically deliver sediment that consists of 70% fines and 30% other materials (including sand).
Therefore, the quantity of fines deposited at the beach under natural sediment delivery far
exceeds that proposed by the program.
Moffatt & Nichol Engineers