5.3. Beach toe elevationSallenger e

5.3. Beach toe elevation
Sallenger et al. (2001)used LIDAR to measure the
toe elevation of the dune (Td) along a 55 km reach of the
northern Outer Banks of NC and found that long-term
erosion correlated negatively withTd, i.e., larger erosion
occurred for small Td where run-up can attack the
foredune more easily than where Td is higher. In
addition to this cross-shore process, it was found that
where there was a deficit of sand, there were lower
dunes, which may be related to gradients in alongshore
sediment transport. Hence, there may be a feedback
between cross-shore erosion processes and alongshore
sediment transport gradients. Wave climate along this
stretch of open North Carolina coastline is essentially
uniform. This contrasts with processes in southern
Monterey Bay, where there is plentiful sand (from the
Fig. 10. South Fort Ord dune recession (left ordinate) for 1940–2004
(line) compared with monthly average mean sea level (right ordinate
with arbitrary datum) at San Francisco. El Niño winters are indicated.
54 E.B. Thornton et al. / Marine Geology 229 (2006) 45–58
dune) and a large gradient of wave energy, where both
erosion and Td are positively correlated with wave
energy. Hence, larger erosion occurs where wave energy
is larger and Td is higher, just the opposite of what
Sallenger et al. (2001)observed.
5.4. Sand mining impact
Although the shoreline in Monterey Bay has
historically eroded as sea level has risen, sand mining
operations appear to have exacerbated the record of
erosion. Sand was continuously extracted from the
shoreface starting in 1906 and continued until the late
1980s, when surf zone sand mining ceased in both Sand
City and Marina. The mined sand ranged in size from
10 mm pebbles to 0.15 mm fine sands. The median grain
sizeminedatbothSandCityandMarinawas
approximately 0.85 mm. The sands at both locations
are generally finer in the summer months when finer
sands are moved shoreward by summer swell waves,
during which time the operations were sometimes
suspended. In this area, the sand is transported

Hasil (Bahasa Indonesia) 2:

5.3. Pantai kaki elevasi
Sallenger et al. (2001) menggunakan LIDAR untuk mengukur
elevasi kaki dari gundukan (Td) sepanjang 55 km jangkauan
Outer Banks utara NC dan menemukan bahwa jangka panjang
erosi berkorelasi negatif withTd, yaitu erosi yang lebih besar
terjadi untuk Td kecil di mana run up dapat menyerang
foredune lebih mudah daripada di mana Td lebih tinggi. Di
samping proses cross-shore ini, ditemukan bahwa
di mana ada defisit pasir, ada lebih rendah
bukit pasir, yang mungkin berhubungan dengan gradien di sejajar
transportasi sedimen. Oleh karena itu, mungkin ada umpan balik
antara proses erosi lintas pantai dan sejajar
gradien transportasi sedimen. Iklim gelombang sepanjang ini
hamparan terbuka North Carolina pantai pada dasarnya
seragam. Hal ini bertentangan dengan proses di selatan
Monterey Bay, di mana ada pasir berlimpah (dari
Gambar. 10. South Fort Ord dune resesi (kiri ordinat) untuk 1940-2004
(baris) dibandingkan dengan rata-rata permukaan laut bulanan (ordinat yang tepat
dengan sewenang-wenang datum ) di San Francisco. El Niño musim dingin yang ditunjukkan.
54 EB Thornton et al. / Geologi Kelautan 229 (2006) 45-58
dune) dan gradien besar energi gelombang, di mana kedua
erosi dan Td berkorelasi positif dengan gelombang
energi. Oleh karena itu, erosi yang lebih besar terjadi di mana energi gelombang
lebih besar dan Td lebih tinggi, hanya kebalikan dari apa yang
Sallenger et al. (2001) mengamati.
5.4. Dampak penambangan pasir
Meskipun garis pantai di Monterey Bay telah
historis terkikis sebagai permukaan laut telah meningkat, penambangan pasir
operasi tampaknya telah memperburuk catatan
erosi. Pasir terus menerus diekstraksi dari
shoreface mulai tahun 1906 dan berlanjut sampai akhir
1980-an, ketika penambangan pasir zona surfing berhenti di kedua Pasir
Kota dan Marina. Pasir ditambang merentang dari
10 mm kerikil 0,15 mm pasir halus. Median butir
sizeminedatbothSandCityandMarinawas
sekitar 0,85 mm. Pasir di kedua lokasi
umumnya lebih baik dalam bulan-bulan musim panas ketika halus
pasir digerakkan menuju ke pantai oleh gelombang membengkak musim panas,
selama waktu operasi kadang-kadang
ditangguhkan. Di daerah ini, pasir diangkut