Tone River

De Rijke's inaugural undertaking in Japan involved the enhancement of the Tone River, which was affected by significant navigable depth issues arising from siltation.^[15] Addressing this issue required detailed topographical survey data, which was not readily available in Japan at the time. Following De Rijke's arrival, an extensive levelling project was commenced in the area. Jack Lindo had already established a baseline level (the Tokyo level) for this purpose.^[7]: 152

While levelling was a known concept in Japan, logistical challenges in procuring appropriate survey instruments hampered progress. De Rijke noted in a letter dated 7 June 1884, "The Japanese still work astonishingly slowly. Now, after a year of measuring, I still cannot even determine the gradient”.^[16]

He later collaborated with Rouwenhorst Mulder on this project; they devised a plan in 1887, which commenced in 1888. The project was executed on a grand scale, employing 3,000 individuals, including many prisoners. The canal was completed by 1890.^[7]: 306

Yodo River Regulation

A significant undertaking was the regulation of the Yodo River, aimed at enhancing its utility as a navigational channel between Osaka and Kyoto. The impetus for this project arose from the progressive shallowing of the river at its mouth, attributed to sediment accumulation. This sedimentation, a consequence of soil erosion in the upstream mountainous regions, considerably augmented the river's sediment load, depositing in the lower stretches and the delta. Consequently, a contemporary bank protection design was implemented at the points of severe erosion. The Dutch engineers De Rijke and Escher introduced the construction of groynes, drawing inspiration from the brushwood groynes used in the Netherlands. The onsite execution of these projects was significantly influenced by Foreman Johannes Westerweel.

A notable environmental concern was the deforestation at the summit of Mount Kabatayama, leading to pronounced surface erosion and additional sediment deposition in the Yodo River. As a remedial measure, the engineers recommended prohibiting logging activities on the mountain slopes and advocated for the reforestation of the mountain's apex. These interventions, over time, proved successful in mitigating the silting issues in the downstream sections of the river.^{[7]: 344 [17]} These initiatives were termed "mountain works" by De Rijke, initially comprising fascine bundles (wiepen) on the slopes, later evolving into hedge-like structures.

Concurrently, the collapse of a retaining wall along the Minato River presented an additional challenge. This was addressed by constructing a bank with a gentle incline, reinforced with stone deposits.

The primary phase of the Yodo River improvements spanned the years 1875-1876. This phase involved deepening the river's channel along the 44 km stretch between Osaka and Kyoto, creating a "summer bed." By installing groynes and dumps, the engineers ensured the maintenance of this low-water bed through focused water currents. During periods of high discharge, the entire winter bed was utilized for drainage, effectively preventing hazardous flooding. This methodology mirrored the techniques employed in the normalization of the Rhine and later, the Meuse rivers in the Netherlands.

The riverbank and groyne constructions were based on traditional Dutch fascine mattress designs, assembled and installed under Westerweel's supervision. In safeguarding the embankments, another Dutch method involving Fascine was employed, overseen by specialist Foreman Josinus Kalis. Notably, local materials like bamboo and rice straw were utilized instead of the customary willow wood and rye straw from Holland. A hallmark of the Dutch engineers' approach was their aim to address multiple objectives through their projects, such as curbing soil erosion, disease prevention, and agricultural enhancement, all within an integrated framework that viewed a river's catchment area as a cohesive system requiring balanced water distribution.

Mikuni Harbour Project

In the latter half of the 19th century, the port of Mikuni, historically a hub of national trade on the Kitamaebune shipping route, faced a decline due to sediment deposits from the Kuzuryū River. Recognising its strategic importance, the local populace in 1875 petitioned the Japanese government for improvements. This led to the involvement of Escher and de Rijke.^[18]

Escher's tenure began in 1876 with an ambitious design including an arc breakwater to counteract gravel run-off, and a basin with an average water depth of three metres. Beyond the maritime aspects, Escher's vision extended to urban development, notably designing an Elementary school in Mikuni. However, financial constraints and contractual terminations led to Escher's return to the Netherlands, leaving the project incomplete.^[6]

In 1877, Johannis de Rijke assumed the mantle. De Rijke, already grappling with existing responsibilities, faced a challenging task exacerbated by frequent disputes with Japanese executive staff and a devastating cholera outbreak in the summer of 1879. His wife's illness added further personal strain, and necessitated her temporary relocation to Kobe for health reasons.^[18]

De Rijke's tenure was marked by significant alterations to Escher's initial plans. Concerns over budget miscalculations and the structural integrity of the arc breakwater, deemed inadequate against the formidable waves, led to a comprehensive redesign. De Rijke's proposal incorporated five layers of fascine mattresses and timber piles, bound by iron chains, and included the addition of four spur dikes. These changes, however, resulted in a tripling of construction costs, imposing a heavy financial burden on the local inhabitants.^[19]

In a desperate bid to generate revenue, the port was prematurely opened for trade in 1880, despite the incomplete state of construction. This decision proved to be ill-fated; the following year witnessed the partial destruction of the arc breakwater by strong ocean waves. Nonetheless, construction persevered, with the project finally reaching completion in 1885. The total cost escalated to 7.5 times Escher's original estimate, but the completion of Mikuni port reinstated its status as a modern trade hub and a pivotal transit point.^[18]

Escher and de Rijke's legacy of engineering solutions employed at Mikuni port included the adoption by Japanese engineers of the fascine mattress technique. The project not only resolved the issue of drift sand but also became a learning ground for Japanese officials and engineers, facilitating the transmission of valuable construction methodologies.^[18]

Locally, the harbour dam is referred to as "Essuru Tsutsumi" or "Escher's Harbour Dam", a homage to its original designer. This dam continues to be an integral component of the Mikuni harbour infrastructure.^[7]: 252

Kiso Delta Regulation

The city of Nagoya, along with its surrounding areas, has historically grappled with the challenges posed by water management, frequently facing flooding from the Kiso Delta at the confluences of the Kiso River, the Nagara River, and the Ibi River. Efforts to regulate these rivers date back to the Edo period, yet these early attempts largely failed to yield significant results. In the period spanning 1878 to 1900, De Rijke undertook extensive research in this region and subsequently developed a comprehensive plan aimed at segregating the three rivers in the lower stretches of the Kiso Delta.

The proposed project was a monumental undertaking, with an estimated cost of 9.74 million yen, a figure representing over 10% of the national budget at the time. The execution of this ambitious plan extended until the year 1912, reflecting the scale and complexity of the intervention required to address the long-standing water management challenges in this region.^[7]: 313

Kiso Lock Construction

The alteration of the confluence points of the Kiso River and the Nagara River consequentially disrupted the direct shipping route between these rivers. The resultant disparity in water levels between the two rivers rendered a simple crossing infeasible. To address this issue, the construction of a lock was proposed as the optimal solution. This lock, pivotal in facilitating navigation, was built over a decade, from 1892 to 1902. Upon its completion in 1902, it witnessed substantial usage, with 20,000 ships passing through it that year. However, as shipping technology progressed and vessel sizes increased, the lock's relevance diminished due to its limited dimensions of 5.5 x 36 metres.

Presently, the lock is situated within the Sendohira River Park, where it stands as a monument commemorating this engineering feat.^[20] A statue of de Rijke is located near the site.^[21]

Dam Construction on the Otani River

Situated approximately 1 km upstream from the confluence of the Yoshino and Otani rivers, this dam represents a significant engineering achievement. Designed and supervised by de Rijke himself, the dam's construction spanned from 1886 to 1887. This structure, essentially a stepped spillway, was conceived as an anti-erosion measure to mitigate the energy dissipation of water flow.

The original dimensions of the dam were 97 metres in length, 12 metres in width, and 3.8 metres in height. Subsequent structural modifications led to a reduction in its length to 60 metres, an alteration aimed at reinforcing the dam's integrity. The Otani River, characteristically dry except during periods of heavy rainfall, transforms into a torrential flow during such events. This dam is one of the few remaining structures in the area that were designed and built under the guidance of de Rijke.^[22]

The Holland Dams

In the realm of hydraulic engineering during the Meiji era, the construction of the dam in Otsu-shi, conceptualised in 1889, stands as a notable example. Japanese engineer Tanabe Gisaburo played a pivotal role in its design, under de Rijke's supervision. This dam, colloquially known as Oranda Sekihisage (Dutch dam), mirrors the architectural blueprint of the Otani dam, featuring a stepped spillway comprising twenty tiers. It is constructed using granite blocks, each measuring 120 cm in length, 55 cm in breadth, and 35 cm in height.

The dam spans a width of 34 metres and rises to a height of 7 metres. Today, it is celebrated as one of the oldest extant industrial heritage sites from the Meiji era. In recognition of its historical and engineering significance, it was accorded the status of an industrial heritage site by the Japanese Association of Civil Engineers in 2004. A similar dam, sharing the same name, was erected in Kaizu-shi by De Rijke in 1891.^[22]

Joganji River Flood Protection

In 1891 de Rijke was involved in works at the Joganji River in Fukuyama-ken, after it was discerned that the river lacked adequate storage capacity to handle excessive rainfall. This deficiency was starkly highlighted by the Ansei dike breach, resulting in the inundation of over 1,500 hectares of land. In response to this event, de Rijke was commissioned to devise a comprehensive flood protection strategy for the region.

His proposal encompassed an array of measures, including the construction of twelve bank defences to safeguard agricultural zones, the establishment of a double dike system, downstream river regulation, and the enhancement of the river's storage capacity through riverbed widening.

The implementation of this ambitious project commenced in 1903. Although de Rijke departed in 1906, the project continued under different stewardship and reached completion in 1926. A contemporaneous photograph bears the caption: "Johannes de Rijke, an engineer employed by the Ministry of the Interior, who suffered the results of it flooding in 1899, once described it as 'not a river, but a waterfall.' The plan involves an investment of a substantial 10,000 yen for the river's renovation, initiating erosion control work on the upstream Yukawa River from 1901, projected over a 20-year period.” De Rijke himself characterised the Joganji River as more akin to rapids than a conventional river.^[7]: 337

Development of the Port of Osaka

The genesis of the Port of Osaka's modernisation can be traced back to 1875, when De Rijke and Van Doorn initially proposed a plan for its enhancement. However, the prohibitive costs associated with their proposal led to its deferment. A resurgence of interest emerged in 1890, driven by the industrial and commercial sectors. The Osaka governor, acknowledging these pressures, requested De Rijke to formulate a revised plan. Central to De Rijke's revised proposal was the redirection of the Yodo River away from the port to mitigate silt accumulation and enhance navigability. This plan, devised in 1890, also aimed to address the flood risks evidenced by recent inundations along the Yodo.

Despite the plan's strategic foresight, it remained unimplemented initially. However, by 1892, with increased financial resources, De Rijke received a commission to refine and advance his proposal. This phase involved meticulous surveying and soil analysis, revealing notably soft ground conditions. De Rijke's design approach drew inspiration from the IJmuiden sea lock in the Netherlands and the Port of Tanjung Priok in the Dutch East Indies. The completion of this comprehensive plan occurred in 1894, though its ambitious scope rendered it a costly venture. An investigative committee, considering military implications, further recommended expanding the scope of the plan, thereby escalating its cost.

This process, marked by significant disagreements between De Rijke and the Japanese bureaucracy, eventually culminated in 1897 with the adoption of a plan that incorporated several elements of De Rijke's original proposal. Despite this, the plan was officially credited to Japanese engineers, and De Rijke was not appointed as the director of the construction office for the new port. This role was instead assigned to Okino Tadao, a Japanese engineer with French training.^[7]: 339

Port of Yokohama Developments

The period from 1886 to 1889 witnessed the collaboration of Johannis de Rijke with A.T.L. Rouwenhorst Mulder in crafting a comprehensive plan for the augmentation of the Port of Yokohama. Concurrently, an alternative proposal was presented by the British engineer Henry Spencer Palmer. The port's redevelopment was funded in part by reparations from the United States following the Shimonoseki campaign.^[18]

Detailed analyses and reports in 1888 by engineers Koi Furuichi, Gisaburo Tanabe, and Mulder revealed the near-identical nature of the plans in terms of overall layout, but differed fundamentally in the construction of the breakwaters. However, political forces swayed the decision on which plan to proceed with.^[18]

Despite the expert recommendations favouring De Rijke's design for its practicality and adaptability, the Japanese government, in a move influenced heavily by diplomatic considerations, opted for Palmer's proposal in 1889. The execution of Palmer's plan encountered significant delays, attributed primarily to the substandard quality of the concrete used. This factor extended the project's completion timeline until 1896.^[23]

A critical aspect of this developmental phase was the contrasting levels of diplomatic support each proposal received. The English engineers benefitted from robust backing through British diplomatic channels, whereas their Dutch counterparts received negligible support from the Netherlands government. The fundamental disparity between the two designs lay in their foundational approaches: De Rijke's plan was predicated on the use of fascine mattresses, a decision informed by the soft soils of the port's seabed. In contrast, Palmer's concrete-based design was deemed excessively rigid for such ground conditions.^[18]

The Japanese government's decision to proceed with Palmer's design precipitated a contentious and public dispute, often played out in the press with protracted written correspondences, during which allegations of corruption were levelled against several officials.^[7]: 297

Other Projects in Japan

De Rijke's engineering expertise extended to a multitude of projects across Japan, each contributing significantly to the country's infrastructural development.^[24][25][16]

His involvement included:

• Chikugo: River improvement works.
• Hiroshima: Development of a comprehensive port plan.
• Katsura: River improvement and management.
• Kobe: Designing of jetties for maritime infrastructure.
• Kuzuryu: River improvement to enhance water flow and management.
• Nagasaki: Crafting a strategic port plan.
• Niigata: Harbour construction and development.
• Sakai: Formulation of a port development plan.
• Shinano: River improvement for better water resource management.
• Tokyo: Comprehensive port plan, along with improvements in sewerage and water supply systems.
• Yokkaichi, Yoshino: River improvement and reforestation efforts, aimed at environmental restoration and flood control.