Sendai Port M Gamo Lagoon （ 8 Hmax 6 Wave Gauge 4 2

Beach Morphological Changes on Sendai Coast by Typhoon Lionrock

Yuta MITOBE, Lecturer Akihiro SUZUKI Daisuke KOMORI, Associate Professor Tohoku Gakuin University, Tagajo Japan Tohoku University, Sendai, Japan Tohoku University, Sendai, Japan

Hitoshi TANAKA, Professor Makoto UMEDA, Associate Professor Yoshiya TOUGE, Assistant Professor Tohoku University, Sendai, Japan Tohoku University, Sendai, Japan Tohoku University, Sendai, Japan 1. Introcduction ~ Typhoon Lionrock, 2016 Route of Typhoon Lionrock (from JMA web-site) - First typhoon to approach and hit Tohoku Area from Pasific Ocean in the observation history of Japan

- Causing severe damages by heavy rain in Tohoku and Hokkaido Areas

- The time of high tide was approximately same as the arrival JMA (Japan Meteorological Aagency): time of the typhoon https://www.data.jma.go.jp/fcd/yoho/typhoon/route_map/bstv2016.html - Field survey on Sendai Coast during and soon after the typhoon events in order to investigate the magnitude of the high tide and high waves and their effects on sediment transport processes - Aerialphoto analysis of morphological changes and their long-term effects 1. Introcduction ~ Sendai Coast (1) wave conditions Study Area: Sendai Coast (12 km sandy beach) Observed Wave Height (by NOWPHAS)

） 10

Tide Gauge Sendai Port m Gamo Lagoon （ 8 Hmax 6 Wave Gauge 4 2

Wave Height Height Wave H 0 1/3 Aug 1 Aug 6 Aug 11 Aug 16 Aug 21 Aug 26 Aug 31 0:00 0:00 0:00 0:00 0:00 0:00 0:00

Observed Tide Level (from JMA website) 150 Idoura Lagoon 100 Observed 50 0 2km Yuriage Port -50 Tide Level (cm) Level Tide Calculated 0.5 m rise by the typhoon Google Earth -100 0 3 6 9 12 15 18 21 0 Aug 30 Aug 30 Aug 31 1. Introcduction ~ Sendai Coast (2) Effect of 2011 tsunami Study Area: Sendai Coast Effect of the 2011 Great East Japan Earthquake Tsunami N Sendai Port Nanakita Gamo Lagoon 200 m Gamo Lagoon

2011/ 3/ 6 (5 days before tsunami) Riv.

Erosion and breaching Idoura Lagoon 2011/ 3/ 12 (1 day after tsunami)of sand dune

Yuriage Port 2km Erosion after tsunami Google Earth 2013/ 3/ 4 (2 years after tsunami) Remaining effect on the beach process 1. Introcduction ~ Sendai Coast (3) Aerial photographs Study Area: Sendai Coast Aerial photographs

Sendai Port - Period: 1992 ~ Current Gamo Lagoon - Frequency: every 1 or 2 months - Altitude: approximately 900m - Conditions: digital camera resolution: approximately 9 cm/pixel approximately 60 % overlap

Idoura Lagoon 1. Shoreline analysis Long-shore sediment transport - to quantify morphological changes - to evaluate long-term effect of this event Yuriage Port 2km 2. Stereo Image Analysis Google Earth - to discuss sediment transport induced by the typhoon more in detail 2. Field Survey ~ A: Sendai Port to Nanakita River mouth

Sendai Port ~ Nanakita River Mouth Photo: Mar. 4, 2016 Sendai Port N Gamo Lagoon A Sendai Port Gamo Lagoon

Nanakita Riv.

Yuriage Port 2km Google Earth Erosion of embankment toe by the waves Data SIO,NOAA, U.S. Navy, NGA, GEBCO Image © 2016 Terra Metrics High waves during the typhoon event 2. Field Survey ~ A: Sendai Port to Nanakita River mouth

Sendai Port ~ Nanakita River Mouth Photo: Mar. 4, 2016 Sendai Port N Gamo Lagoon A Sendai Port Gamo Lagoon

Nanakita Riv.

Before Typhoon (Aug. 8) After Typhoon (Aug. 31) 2. Field Survey ~ A: Sendai Port to Nanakita River mouth

Sendai Port ~ Nanakita River Mouth Photo: Mar. 4, 2016 Sendai Port N Gamo Lagoon A Sendai Port Gamo Lagoon

Nanakita Riv.

After Typhoon (Aug. 31) During Typhoon (Aug. 30) Sediment transport over the sand dune 2. Field Survey ~ B: Arahama Coast

Arahama Coast Photo: Mar. 4, 2016 Sendai Port NN Gamo Detached Lagoon Breakwater

3.8m

Maximum run-up height: approx. 4 m

Lower than the previous height of the coastal dykes (before the 2011 tsunami event: 5.2 m from MSL) 2. Field Survey ~ C: Natori River Mouth

Natori River Mouth Photo: Mar. 4, 2016 Sendai Port Yuriage Port Gamo Lagoon N Construction of Jetty new coastal dyke

Idoura Lagoon 3. Aerial photo Analysis ~ Stereo Image Analysis Stereo Image Analysis around Nanakita River Mouth 3D Topographical Data Aerial Photos on Sep. 1, 2016

DSM (Disital Surface Model): 1m-mesh 8 Elevation (m)

0 3. Aerial photo Analysis ~ Stereo Image Analysis Stereo Image Analysis around Nanakita River Mouth DSM on July 12, 2016 (m) 2016/7/12

2016/9/1

Nanakita Riv. (m) DSM on Sep. 1, 2016 (m) 2 Deposition

- 2 Erosion 3. Aerial photo Analysis ~ Shoreline Analysis Longshore Shoreline Change (y0: shoreline sediment transport Sendai Port ~ Nanakita River Mouth position on July 12, 2016) 50 July 12, 2016 Jetty Nov. 5, 2016

0 0

- (m)

Gamo Lagoon y -50 Nanakita Riv. Oct. 1, 2016 Sep. 1, 2016 Rapid recovery Sep. 1, 2016 -100 on updrift side 30 m retreat -150 0 200 400 600 800 1000 1200 1400 1600 1800 x (m) Oct. 1, 2016 Time series of shoreline positions after the 2011 tsunami

400 Nov. 5, 2016 Oct. 1, 2016 Nov. 5, 2016 Typhoon Lionrock 200

(m) 2011 tsunami

y July 12, 2016 0 Sep. 1, 2016

-200 0 200 400 600 800 1000 1200 1400 1600 1800 x (m) 3. Aerial photo Analysis ~ Shoreline Analysis Longshore Shoreline Change (y0: shoreline sediment transport Arahama Coast position on July 12, 2016) 40 Detached breakwater July 12, 2016 Nov. 5, 2016

20 Oct. 1, 2016 (m)

0 0 y

- 20 m retreat Recovered Sep. 1, 2016 y -20 in 1 month Sep. 1, 2016 -40 5200 5400 5600 5800 6000 6200 6400 6600 x (m) Oct. 1, 2016 Time series of shoreline positions after the 2011 tsunami Typhoon Lionrock

300 Nov. 5, 2016 Nov. 5, 2016

200Oct. 1, 2016 (m)

y 100 Sep. 1, 2016 2011 tsunami 0 July 12, 2016 -100 5200 5400 5600 5800 6000 6200 6400 6600 x (m) 3. Aerial photo Analysis ~ Shoreline Analysis Longshore Shoreline Change (y0: shoreline sediment transport Natori River Mouth position on July 12, 2016) 100 July 12, 2016

50 Oct. 1, 2016 Nov. 5, 2016 (m)

Idoura Lagoon 0 y Sep. 1, 2016 Natori Riv. - 0 Sep. 1, 2016 y

-50 9500 10000 10500 11000 20 m retreat x (m) Rapid recovery Oct. 1, 2016 Mar. 6, 2011 (before 2011 tsunami)

1000 Nov. 5, 2016 800 Wave dissipating Jetty 600 Mar. 12, 2011 (after 2011 tsunami) (m) Structure Nov. 5 , 2016 y 400 Oct. 1, 2016 200 Sep. 1, 2016 0 July 12, 2016 to block longshore sediment transport 9500 10000 10500 11000 x (m) => rapid recovery on the updrift side 3. Aerial photo Analysis ~ Shoreline Analysis Longshore Shoreline Change (y0: shoreline sediment transport Natori River Mouth position on July 12, 2016) 100 July 12, 2016

50 Oct. 1, 2016 Nov. 5, 2016 (m)

Idoura Lagoon 0 y Sep. 1, 2016 Natori Riv. - 0 Sep. 1, 2016 y

-50 9500 10000 10500 11000 20 m retreat x (m) Rapid recovery Oct. 1, 2016 Time series of shoreline positions after the 2011 tsunami

1000 Nov. 5, 2016 800 Wave dissipating Jetty 600 (m) Structure Nov. 5 , 2016 y 400 Oct. 1, 2016 200 Sep. 1, 2016 0 July 12, 2016

9500 10000 10500 11000 x (m) 3. Aerial photo Analysis ~ Shoreline Analysis Longshore Whole area Cross-shore movement sediment transport of sediment is dominant Yuriage Port Sendai Drainage Detached 1000 Port July 12, 2016 Wave-dissipating Channel Breakwater Structure Oct. 1, 2016 Nov. 5, 2016

(m) 500 Arahama Coast y 0 Gamo Lagoon Idoura Lagoon Nanakita Riv. Sep. 1, 2016 Natori Riv. 100 July 12, 2016 50 Oct. 1, 2016 Nov. 5, 2016

(m)

0 y

– -50 Sep. 1, 2016

y y No sandy beach -100 due to erosion after -150 the 2011 tusnami 0 2000 4000 6000 8000 10000 x (m) More recovery on the updrift side of the river, the detached break and also the structures intruding into coast line due to the erosion by the 2011 tsunami

Slower recovery due to loss of sediment by wave overtopping 3. Aerial photo Analysis ~ Shoreline Analysis Longshore Whole area sediment transport Yuriage Port Sendai Drainage Detached 1000 Port Wave-dissipating Channel Breakwater Structure

(m) 500 Arahama Coast y 0 Gamo Lagoon Idoura Lagoon Nanakita Riv. Natori Riv. 100 50 July 6, 2017

(m)

0 y

– -50 y y -100 -150 0 2000 4000 6000 8000 10000 x (m) Including the lagoon areas, shoreline positions recovered in one year and no remaining effect has been observed. 4. Conclusions

Field survey during and soon after the typhoon Lionrock - Maximum runup height: about 4 m from MSL Lower than the original height of the coastal dykes (5m) in this area - Severe erosion of the embankment toe near Sendai Port - Wave overtopping of the sand dunes of both Gamo and Idoura Lagoons Sediment transport over the sand dunes

Aerial photo analysis - 20 ~ 30 m retreat of shoreline in whole area which is not the most significant after the 2011 tsunami - More rapid and larger recovery was observed on the updrift sides of river, detached breakwater and structures intruding into coast line due to the effect of the 2011 tsunami - Deposition of sediment along the seaward toe of the coastal dyke No significant effect on shoreline changes - Slower recovery around the lagoon areas which seem to be caused by the loss of the sediment due to the sediment transport by the wave overtopping - No remaining effect of this event was observed after 1 year from the event