De tijdspiegel, ’s Gravenhage, 1860, p. 244.
 Geïllustreerde encyclopaedie. Woordenboek voor wetenschap en kunst, beschaving en nijverheid. Deel 13. Anthony Winkler Prins, 1880, pp. 313-315.
 Compared to neighbouring countries, there were two reasons for this sluggish development. In the first place, there was already a satisfactory alternative: canal barges and stagecoaches offered a fully developed public transport infrastructure, with concomitant timetables. Furthermore, the boggy surfaces remained a major impediment for technically reliable construction of railways. cf. Jan de Vries, Barges and Capitalism. Passenger Transportation in the Dutch Economy, 1632-1839, A.A.G. Contributions, 21, Wageningen, 1978, pp. 33-400 and Auke van der Woud, Een nieuwe wereld, Amsterdam, 2007, pp. 283-292.
 Harry Lintsen, Ingenieur van beroep, The Hague, 1985, pp. 38-39.
 The large-scale reconstruction of the Netherlands was partly due to the modernisation of invisible structures: the new constitution of 1848 and ensuing legislation established the hierarchical relationship between the government, parliament and the underlying provincial and municipal tiers.
 G.P.J. Verbong, ‘Delftse ingenieurs tussen wetenschap en industrie (1875-1900)’, Gewina 16, 1993, 248-260, pp. 255-256. From 1871 it was possible for girls to attend HBS, albeit by ministerial consent. By 1906 however, girls were finally admitted without restriction.
 Non-military engineers were called civil engineers. In those days the course focused on core subjects, such as mathematics, theoretical and applied mechanics, and physics. Verbong, 1993.
 Verbong, 1993, p. 251.That means that in 1875, 1 in 29,996 of the population was a trainee civil engineer. By comparison: in 2019, 1 in 10,112 of the population was studying civil engineering at a Dutch technical university. See: CBS and https://www.studiekeuze123.nl/
 ‘Normalisation’ of rivers became common in the 19th century and was a way of controlling hitherto unpredictable river flows through canalisation.
 Established in 1798, Rijkswaterstaat had overall responsibility on behalf of the state for water management in the Netherlands. Over the years its responsibilities expanded to include other forms of infrastructure. Rijkswaterstaat's official name in English is the Directorate-General for Public Works and Water Management.
 R.A. van Sandick, ‘J. de Koning’, De Ingenieur, vol. 21, no. 50, 1906, pp. 957-962.
 J.M.K. Pennink, ‘Ir. J. van Hasselt’, De Ingenieur, vol. 32, no 16, 1917, pp. 282-285.
 Rijkswaterstaat commenced systematic normalisation of the Waal in 1875. H.W. Lintsen (ed.), Geschiedenis van de Techniek in Nederland. De wording van een moderne samenleving 1800-1890. Deel II, Zutphen, 1993, p. 122.
 R.A. van Sandick, 1906, p. 958.
 125 years Royal Haskoning 1881-2006, Nijmegen, 2006, p. 115.
 Acting as a representative of other companies.
 In a letter of 31 March 1882 to their civil-law notary Mr Böhtlingk, E.J. Hubertus, ‘Een eeuw Haskoning’, Hakoerier 81/1, pp. 2-5, p. 3.
 J.M.K. Pennink, 1917, p. 284.
 R.A. van Sandick, 1906.
 These, moreover, were much more reliable than the typical, hitherto widely used Dutch windmill. H.W. Lintsen (ed.) 1993, p. 97.
 A competitor firm even had its own steam engine factory: Atlas in Amsterdam. In 1875, the founders promoted themselves as: the engineering firm for the steam-powered pumping station. See Algemeen Handelsblad 1875, 19 and 23 March.
 J.M.K. Pennink 1917 and L. ten Hag et al. Stoomgemaal De Tuut. Een monument van gemeenschapszin, Meppel, z.j., pp. 68-71.
 R. VerLoren van Themaat, ‘80 jaar ingenieursbureau J. van Hasselt en de Koning’, De Raadgevend ingenieur, vol. 1, no. 11, juli 1959, pp. 225-231, p. 230.
 Drijfveren, 100 jaar Haskoning, December 1981, pp. 38-39.
 Company archives Royal HaskoningDHV.