An entertaining puzzle from Gozo. Obscure/specialist knowledge is not required today.
The across answers are all geographical features, of water and land. Thank you Gozo.

| ACROSS | ||
| 1 | CATARACT | Trouble in sight of cascade (8) | 
| double definition | ||
| 5 | STRAND | Maroon thread (6) | 
| double definition | ||
| 9 | MERIDIAN | Midday on the Circle line? (8) | 
| double/cryptic definition | ||
| 10 | GEYSER | Old Faithful Y-reg Seat half-rebuilt (6) | 
| anagram (rebuilt) of Y-REG and SEat (half of) | ||
| 12 | OASIS | Refuge that is old and unaltered (5) | 
| O (old) and AS IS (unaltered) | ||
| 13 | CATCHMENT | Security guards out west in court area around school (9) | 
| wATCHMEN (security guards) missing (out) W (west) inside CT (court) | ||
| 14 | CORRIE | Soap in basin (6) | 
| double definition – a bowl on a mountainside and the soap opera Coronation Street | ||
| 16 | TERRAIN | Turtle avoids soft tract of land (7) | 
| TERRApIN (turtle) missing (avoids) P (piano, soft) | ||
| 19 | NARROWS | Straits at pole with direction indicators (7) | 
| N (north, a pole) and ARROWS (direction indicators) | ||
| 21 | MASSIF | Range of service provided (6) | 
| MASS (religious service) and IF (provided) | ||
| 23 | RESERVOIR | River rose – burst bank (9) | 
| anagram (burst) of RIVER ROSE | ||
| 25 | BUTTE | Isolated hill with tree-top in Scottish isle (5) | 
| Tree (first letter, top) inside BUTE (Scottish isle) | ||
| 26 | SPRING | Well before summer (6) | 
| double definition | ||
| 27 | ICE WATER | This melt-down transformed one wet acre (3,5) | 
| anagram (transformed) of I (one) WET ACRE | ||
| 28 | SEA-BED | Main base? (3-3) | 
| cryptic definition | ||
| 29 | WELL HEAD | First sight of 26 brings future leaders’ pledge (8) | 
| WE’LL HEAD (we will head, future leader’s pledge) | ||
| DOWN | ||
| 1 | COMMON | Public company taking thousands on (6) | 
| CO (company) with M M (thousand, twice) and ON | ||
| 2 | TURNS SOUR | Goes off organising North USSR tour (5,4) | 
| anagram (organising) of N (north) USSR TOUR | ||
| 3 | RIDES | Spins and dries, perhaps (5) | 
| anagram (perhaps) of DRIES | ||
| 4 | CHANCRE | Risk grabbing Romeo’s ulcer (7) | 
| CHANCE (risk) contains (grabbing) R (Romeo, phonetic alphabet) – a soft chancre | ||
| 6 | THE SHIRES | Hobbits’ home in traditionally hunting areas (3,6) | 
| double definition – my daughter (a Tolkien fanatic) insists that the hobbit region of The Shire must be singular, there is only one | ||
| 7 | AISLE | Passage is covered in drink (5) | 
| IS inside ALE (drink) | ||
| 8 | DERATING | State getting reproof reducing taxes (8) | 
| DE (Delaware, state) with RATING (reproof) | ||
| 11 | AT IT | Tantrist regularly in flagrante delicto (2,2) | 
| every other letter (regularly) of tAnTrIsT | ||
| 15 | RIO GRANDE | Old relative is breaking journey to Trump’s walled river (3,6) | 
| O (old) GRAN (relative) inside (is breaking) RIDE (journey) – part of the US-Mexico border | ||
| 17 | ARISTOTLE | Earl let loose philosopher (9) | 
| ARISTO (aristocrat, an earl perhaps) then anagram (loose) of LET | ||
| 18 | ENTRUSTS | Gives responsibility to new nurses taking temperature twice (8) | 
| anagram (new) of NURSES containing T (temperature) twice | ||
| 20 | STOW | Just five letters for lodge (4) | 
| from S TO W is 5 letters (s t u v w) | ||
| 21 | MIRACLE | Great surprise of family vehicle turning up within distance (7) | 
| CAR (family vehicle) reversed (turning up) inside MILE (distance) | ||
| 22 | SEE RED | Get angry about sight of traffic lights (3,3) | 
| definition/cryptic definition | ||
| 24 | SYRIA | Breezy point up-country (5) | 
| AIRY (breezy) S (south, point of compass) all reversed (up) | ||
| 25 | BOWEL | Waste processing centre‘s smell not entirely healthy (5) | 
| BO (smell) and WELL (healthy) missing last letter (not entirely) | ||
Thanks, Pee Dee. Can you further elucidate 20 down? I’m still stumped by it.
Got it now! Sorry
Another fun themed grid from Gozo which was soon discerned with 10a, my FOI.
The theme was certainly helpful in snagging clues like 21, 25 and 14 – the latter may prove elusive for non-UK solvers though the soap is broadcast overseas.
Once I knew the lie of the land, as it were, the rest fell quickly with 2d, 6d and 11d my favourites. The nose-wrinkling 25d made me laugh given its intersection with 25a.
Thanks to Gozo for continually coming up with the goods and to PeeDee too.
CHANCRE and THE SHIRES were unknowns for me, and I failed to parse WELLHEAD.
Thanks to Gozo and PeeDee. I did better than usual with this setter, but still did not finish. I too started with GEYSER and did figure out STOW but failed to get CORRIE, BUTTE, and WELLHEAD. I also wondered about SHIRES as plural.
Even though I failed with CORRIE ( new to me), needed a word finder for DERATING, and couldn’t parse STOW and CATCHMENT I found this easier than I expected from Gozo. WELLHEAD was a favourite. Thanks to both.
Thanks Gozo and PeeDee
Pretty much the same as NNI@4. Not sure that I enjoyed the solve as much as normal from this setter for some reason, although there were some very good clues throughout. Did grin at the ‘waste processing centre’ when that finally dawned.
Finished in the SE corner with WELLHEAD, that BOWEL and BUTTE.
Thanks for the fun Gozo – it really was. I started by doing all the down clues and then everything made a lot of sense. I also looked sideways at the plural in 6d but thought I must have missed something when I read it all those years ago. Thanks for the explanations PeeDee.
I would just like to point out that yesterday (it is breakfast coffee time here) was GEYSER day as that answer also came up elsewhere.
We also had Rio Grande last week with a similar clue. First time I’ve used the search function which works very easily. DNF as I put chancer and then couldn’t solve 14ac
Same as Contrapunctus@9, although if I had got 4d correctly, I still would have failed on 14a CORRIE. The soap is familiar to us in Canada, but not, I think, its nickname. Thanks PeeDee for explaining those.
Nice puzzle, Gozo. Favourites for their laugh out loud surfaces were 11d AT IT and 25d BOWEL.
thanks GOZO! I liked the tantrist. I also thought “range of service provided” was smooth. Missed the soap, I’m afraid.
Thanks also PeeDee
Very nice puzzle. I missed 20d: thanks to PeeDee for explaining this!
I thought 1a and 9a were brilliant.
However, I cannot accept that BOWEL is a ‘waste processing centre’: the (small) bowel is in fact where all the goodies in the food are absorbed; the waste is what is left.
Hi Lucio, I took it that the small intestine absorbs the nutrients and the large intestine (the bowel) processes the waste to remove the salt and water that was added during the digestion. Otherwise you would run out of salt and water and get dehydrated.