science

Hydrological code

Hydrological code is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Hydrological code rather than just read about it. In short: A hydrological code or hydrologic unit code is a sequence of numbers or letters (a geocode) that identify a hydrological unit or feature, such as a river, river reach, lake, or area like a drainage basin (also called watershed in North America) or catchment. One system, developed by Arthur Newell Strahler, known as the Strahler stream order, ranks streams based on a hierarchy of tributaries.

Key takeaways

Hydrological code belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Hydrological code to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Hydrological code from memory before moving on to harder problems.

Reference excerpt

A hydrological code or hydrologic unit code is a sequence of numbers or letters (a geocode) that identify a hydrological unit or feature, such as a river, river reach, lake, or area like a drainage basin (also called watershed in North America) or catchment. One system, developed by Arthur Newell Strahler, known as the Strahler stream order, ranks streams based on a hierarchy of tributaries. Each segment of a stream or river within a river network is treated as a node in a tree, with the next segment downstream as its parent. When two first-order streams come together, they form a second-order stream. When two second-order streams come together, they form a third-order stream, and so on. Another example is the system of assigning IDs to watersheds devised by Otto Pfafstetter, known as the Pfafstetter Coding System or the Pfafstetter System. Drainage areas are delineated in a hierarchical fashion, with "level 1" watersheds at continental scales, subdivided into smaller level 2 watersheds, which are divided into level 3 watersheds, and so on. Each watershed is assigned a unique number, called a Pfafsetter Code, based on its location within the overall drainage system.

Europe A comprehensive coding system is in use in Europe. This system codes from the ocean to the so-called primary catchment. The system determines a set of oceans or endorheic systems identified by a letter. These systems are subdivided into a maximum of 9 seas. The seas are numbered 1 to 9. Seas lying far from the ocean, for example the Black Sea receive a higher number. The seas are delimited using the so-called definitions made by the International Hydrographic Organization in 1953. The coasts of these seas are defined clockwise from north west to south east from the strait where the sea connects to the ocean or the other seas.

Subsequently every watershed along this coast is assigned a number using the Pfafstetter Coding System. This implies that the four largest watersheds are selected and receive numbers 2,4,6, or 8. The watersheds in between the large systems receive numbers 3, 5, and 7. Numbers 1 and 9 are used for the small watersheds on the edges of the strait. The smaller systems can subsequently be numbered recursively or kept together for grouping purpose. Landmasses (Continent and Islands) are also numbered in a logical manner, along a clock-wise oriented sea. For Europe containing many inner seas this feature helps to read the relative location of a hydrological object in the sea.

United States

See also Hydrologic Unit Modeling for the United States Water Resource Region

References

External links "Hydrologic Unit Geography". Virginia Department of Conservation & Recreation. Retrieved 21 November 2010. "CCM2 Catchments and Rivers of Europe". Joint Research Center of the European Commission. Retrieved 13 September 2012. "Review of Existing River Coding Systems" (PDF). European Coding Systems WFD GIS Working Group. Archived from the original (PDF) on January 21, 2007. Retrieved 29 September 2014.

Worked examples

Example 1 — a first encounter with Hydrological code

Start with the simplest possible case. Write down what Hydrological code claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Hydrological code before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Hydrological code ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Hydrological code

In research: Hydrological code appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Hydrological code in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Hydrological code is common in secondary-school and first-year university syllabi. It links to neighbouring topics Geocodes, Hydrology, Limnology, so understanding it makes those chapters shorter.
In everyday life: Look for Hydrological code outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

Affiliate

Preply — study more efficiently by working with a personal tutor. 50% off.

How to study Hydrological code in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Hydrological code means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Hydrological code out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Hydrological code in simple terms?

Why does Hydrological code matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Hydrological code?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Hydrological code.