The birthplace and end place of a river have different altitudes, and (the birth places are always higher than the ending places.)

I know that another correction gave you more technical terms, but for everyday speech, birthplace and end are fine ;) We also commonly called the birthplace a "headwater", and the end a "mouth".

Or "the start is always higher than the end."

Sometimes the difference ofin altitude can vary from hundreds to thousands of meters.

Let me use the Huai River as an example that t. The atltitude of its birth place is 1140 m, and it flows east to the Huang Sea and East Sea.

If there are no special constructions on the rivers, the upper river and the middle river will be dry, because the water will all flow into the downriver because of the big atdue to the big drop in altitude drop.

To maintainke sure that every reach has water, people have constructed many "water locks" on rivers.

Each section of a river has a "water lock", so that the upriver won't dry up and the downriver won't be flooded.

So "water locks" isare beneficial to water conservancy and agricultural irrigation.

The birthplace (headwaters) and end place (outlet) of a river have different altitudes, and the birth places are always higher than the end places.

We typically call them the headwaters and outlet of a river.

SometimIn some cases, the difference of / in altitude can vary from hundreds to thousands of meters.

“Sometimes” doesn’t really make sense, because the difference for each river never changes.

“Difference in altitude” is more natural.

Let me use the Huai River as an example that t. The he atltitude of its birth place is 1140 m, and it flows east to the Huang Sea and East Sea (0 m).

Not all seas are at an elevation of 0 m (the elevation of the Caspian Sea is -28 m, for example), so it’s better to specify this, in my opinion.

If there are no special constructions on a rivers, the uprivper and the middle sections of the river will be dry, because water will all flow into the dlowner sections of the river [because of / due to] the big atltitude drop.

If there are no special constructions on a river, the upper and the middle sections of the river will be dry, because water will all flow into the lower sections of the river [because of / due to] the big altitude drop.

Using “because” twice in the same sentence doesn’t sound very nice, so I changed it to “due to.”

To maintain thatconsistent water levels in every reach has water, people have constructed many "water locks"dams on rivers.

To maintain consistent water levels in every reach, people have constructed many dams on rivers.

I believe those are called “dams.” Locks are the constructions that allow ships to navigate around the dams.

Each section of a river has a "water lock",dam so that the upriver section won't dry up and the downriver section won't be flooded.

I’ve only ever seen “upriver” and “downriver” used as adjectives, not nouns. For example, “Huainan is upriver from Bengpu, and Tianchang is downriver.”

So "water lock" isdams are beneficial to water conservancy and agricultural irrigation.