Question: How much of the Netherlands is affected by the problem regulated by the Hoogheemraadschap van Rijnland? 
Sentence (from "Flood control in the Netherlands"): River dikes prevent flooding from water flowing into the country by the major rivers Rhine and Meuse, while a complicated system of drainage ditches, canals, and pumping stations (historically: windmills) keep the low-lying parts dry for habitation and agriculture.
Relevant evidence: No