Are the Arakawa anime chapters based off a manga? Each episode has a number of chapters in it, with about 100 in each season.  I think season 1 actually had 105 but season 2 ended with Chapter 200. I am wondering if these chapters are actually based off an Arakawa manga?
There is an Arakawa Under the Bridge manga, and it has a lot of chapters. At the time of writing, the following tankobon volumes exist:


Volume    Chapters
   1        1- 23 (+X)
   2       24- 47 (+X-2)
   3       48- 77 (+X-3)
   4       78-107 (+X-4)
   5      108-136 (+X-5)
   6      137-166 (+X-6)
   7      167-196 (+X-7)
   8      197-225 (+Nakamura Koubou Shutchou-ban, X-8)
   9      226-255 (+X-9)
  10      256-280 (+Shuushoku no Yuusha Recruit, Hige mo Seifuku no Uchi, X-10)
  11      281-301 (+Riku-chan Kinsei Nikki 1, 2, Meikyuu Labyrinth, Tokimeke!! Arakawa Memorial, X-11)
  12      302-325 (+X-12)
  13      326-356 (+Joshi-ryoku Sentai Love East, X-13)